4. Reference
This part of the reference documentation details the various components that comprise Spring for Apache Kafka. The main chapter covers the core classes to develop a Kafka application with Spring.
4.1. Using Spring for Apache Kafka
This section offers detailed explanations of the various concerns that impact using Spring for Apache Kafka. For a quick but less detailed introduction, see Quick Tour.
4.1.1. Connecting to Kafka
-
KafkaAdmin- see Configuring Topics -
ProducerFactory- see Sending Messages -
ConsumerFactory- see Receiving Messages
Starting with version 2.5, each of these extends KafkaResourceFactory.
This allows changing the bootstrap servers at runtime by adding a Supplier<String> to their configuration: setBootstrapServersSupplier(() → …).
This will be called for all new connections to get the list of servers.
Consumers and Producers are generally long-lived.
To close existing Producers, call reset() on the DefaultKafkaProducerFactory.
To close existing Consumers, call stop() (and then start()) on the KafkaListenerEndpointRegistry and/or stop() and start() on any other listener container beans.
For convenience, the framework also provides an ABSwitchCluster which supports two sets of bootstrap servers; one of which is active at any time.
Configure the ABSwitchCluster and add it to the producer and consumer factories, and the KafkaAdmin, by calling setBootstrapServersSupplier().
When you want to switch, call primary() or secondary() and call reset() on the producer factory to establish new connection(s); for consumers, stop() and start() all listener containers.
When using @KafkaListener s, stop() and start() the KafkaListenerEndpointRegistry bean.
See the Javadocs for more information.
Factory Listeners
Starting with version 2.5, the DefaultKafkaProducerFactory and DefaultKafkaConsumerFactory can be configured with a Listener to receive notifications whenever a producer or consumer is created or closed.
interface Listener<K, V> {
default void producerAdded(String id, Producer<K, V> producer) {
}
default void producerRemoved(String id, Producer<K, V> producer) {
}
}
interface Listener<K, V> {
default void consumerAdded(String id, Consumer<K, V> consumer) {
}
default void consumerRemoved(String id, Consumer<K, V> consumer) {
}
}
In each case, the id is created by appending the client-id property (obtained from the metrics() after creation) to the factory beanName property, separated by ..
These listeners can be used, for example, to create and bind a Micrometer KafkaClientMetrics instance when a new client is created (and close it when the client is closed).
The framework provides listeners that do exactly that; see Micrometer Native Metrics.
4.1.2. Configuring Topics
If you define a KafkaAdmin bean in your application context, it can automatically add topics to the broker.
To do so, you can add a NewTopic @Bean for each topic to the application context.
Version 2.3 introduced a new class TopicBuilder to make creation of such beans more convenient.
The following example shows how to do so:
@Bean
public KafkaAdmin admin() {
Map<String, Object> configs = new HashMap<>();
configs.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
return new KafkaAdmin(configs);
}
@Bean
public NewTopic topic1() {
return TopicBuilder.name("thing1")
.partitions(10)
.replicas(3)
.compact()
.build();
}
@Bean
public NewTopic topic2() {
return TopicBuilder.name("thing2")
.partitions(10)
.replicas(3)
.config(TopicConfig.COMPRESSION_TYPE_CONFIG, "zstd")
.build();
}
@Bean
public NewTopic topic3() {
return TopicBuilder.name("thing3")
.assignReplicas(0, Arrays.asList(0, 1))
.assignReplicas(1, Arrays.asList(1, 2))
.assignReplicas(2, Arrays.asList(2, 0))
.config(TopicConfig.COMPRESSION_TYPE_CONFIG, "zstd")
.build();
}
@Bean
fun admin() = KafkaAdmin(mapOf(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG to "localhost:9092"))
@Bean
fun topic1() =
TopicBuilder.name("thing1")
.partitions(10)
.replicas(3)
.compact()
.build()
@Bean
fun topic2() =
TopicBuilder.name("thing2")
.partitions(10)
.replicas(3)
.config(TopicConfig.COMPRESSION_TYPE_CONFIG, "zstd")
.build()
@Bean
fun topic3() =
TopicBuilder.name("thing3")
.assignReplicas(0, Arrays.asList(0, 1))
.assignReplicas(1, Arrays.asList(1, 2))
.assignReplicas(2, Arrays.asList(2, 0))
.config(TopicConfig.COMPRESSION_TYPE_CONFIG, "zstd")
.build()
Starting with version 2.6, you can omit partitions() and/or replicas() and the broker defaults will be applied to those properties.
The broker version must be at least 2.4.0 to support this feature - see KIP-464.
@Bean
public NewTopic topic4() {
return TopicBuilder.name("defaultBoth")
.build();
}
@Bean
public NewTopic topic5() {
return TopicBuilder.name("defaultPart")
.replicas(1)
.build();
}
@Bean
public NewTopic topic6() {
return TopicBuilder.name("defaultRepl")
.partitions(3)
.build();
}
@Bean
fun topic4() = TopicBuilder.name("defaultBoth").build()
@Bean
fun topic5() = TopicBuilder.name("defaultPart").replicas(1).build()
@Bean
fun topic6() = TopicBuilder.name("defaultRepl").partitions(3).build()
Starting with version 2.7, you can declare multiple NewTopic s in a single KafkaAdmin.NewTopics bean definition:
@Bean
public KafkaAdmin.NewTopics topics456() {
return new NewTopics(
TopicBuilder.name("defaultBoth")
.build(),
TopicBuilder.name("defaultPart")
.replicas(1)
.build(),
TopicBuilder.name("defaultRepl")
.partitions(3)
.build());
}
@Bean
fun topics456() = KafkaAdmin.NewTopics(
TopicBuilder.name("defaultBoth")
.build(),
TopicBuilder.name("defaultPart")
.replicas(1)
.build(),
TopicBuilder.name("defaultRepl")
.partitions(3)
.build()
)
When using Spring Boot, a KafkaAdmin bean is automatically registered so you only need the NewTopic (and/or NewTopics) @Bean s.
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By default, if the broker is not available, a message is logged, but the context continues to load.
You can programmatically invoke the admin’s initialize() method to try again later.
If you wish this condition to be considered fatal, set the admin’s fatalIfBrokerNotAvailable property to true.
The context then fails to initialize.
If the broker supports it (1.0.0 or higher), the admin increases the number of partitions if it is found that an existing topic has fewer partitions than the NewTopic.numPartitions.
|
Starting with version 2.7, the KafkaAdmin provides methods to create and examine topics at runtime.
-
createOrModifyTopics -
describeTopics
For more advanced features, you can use the AdminClient directly.
The following example shows how to do so:
@Autowired
private KafkaAdmin admin;
...
AdminClient client = AdminClient.create(admin.getConfigurationProperties());
...
client.close();
Starting with versions 2.9.10, 3.0.9, you can provide a Predicate<NewTopic> which can be used to determine whether a particular NewTopic bean should be considered for creation or modification.
This is useful, for example, if you have multiple KafkaAdmin instances pointing to different clusters and you wish to select those topics that should be created or modified by each admin.
admin.setCreateOrModifyTopic(nt -> !nt.name().equals("dontCreateThisOne"));
4.1.3. Sending Messages
This section covers how to send messages.
Using KafkaTemplate
This section covers how to use KafkaTemplate to send messages.
Overview
The KafkaTemplate wraps a producer and provides convenience methods to send data to Kafka topics.
The following listing shows the relevant methods from KafkaTemplate:
CompletableFuture<SendResult<K, V>> sendDefault(V data);
CompletableFuture<SendResult<K, V>> sendDefault(K key, V data);
CompletableFuture<SendResult<K, V>> sendDefault(Integer partition, K key, V data);
CompletableFuture<SendResult<K, V>> sendDefault(Integer partition, Long timestamp, K key, V data);
CompletableFuture<SendResult<K, V>> send(String topic, V data);
CompletableFuture<SendResult<K, V>> send(String topic, K key, V data);
CompletableFuture<SendResult<K, V>> send(String topic, Integer partition, K key, V data);
CompletableFuture<SendResult<K, V>> send(String topic, Integer partition, Long timestamp, K key, V data);
CompletableFuture<SendResult<K, V>> send(ProducerRecord<K, V> record);
CompletableFuture<SendResult<K, V>> send(Message<?> message);
Map<MetricName, ? extends Metric> metrics();
List<PartitionInfo> partitionsFor(String topic);
<T> T execute(ProducerCallback<K, V, T> callback);
// Flush the producer.
void flush();
interface ProducerCallback<K, V, T> {
T doInKafka(Producer<K, V> producer);
}
See the Javadoc for more detail.
In version 3.0, the methods that previously returned ListenableFuture have been changed to return CompletableFuture.
To facilitate the migration, the 2.9 version added a method usingCompletableFuture() which provided the same methods with CompletableFuture return types; this method is no longer available.
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The sendDefault API requires that a default topic has been provided to the template.
The API takes in a timestamp as a parameter and stores this timestamp in the record.
How the user-provided timestamp is stored depends on the timestamp type configured on the Kafka topic.
If the topic is configured to use CREATE_TIME, the user specified timestamp is recorded (or generated if not specified).
If the topic is configured to use LOG_APPEND_TIME, the user-specified timestamp is ignored and the broker adds in the local broker time.
The metrics and partitionsFor methods delegate to the same methods on the underlying Producer.
The execute method provides direct access to the underlying Producer.
To use the template, you can configure a producer factory and provide it in the template’s constructor. The following example shows how to do so:
@Bean
public ProducerFactory<Integer, String> producerFactory() {
return new DefaultKafkaProducerFactory<>(producerConfigs());
}
@Bean
public Map<String, Object> producerConfigs() {
Map<String, Object> props = new HashMap<>();
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, IntegerSerializer.class);
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
// See https://kafka.apache.org/documentation/#producerconfigs for more properties
return props;
}
@Bean
public KafkaTemplate<Integer, String> kafkaTemplate() {
return new KafkaTemplate<Integer, String>(producerFactory());
}
Starting with version 2.5, you can now override the factory’s ProducerConfig properties to create templates with different producer configurations from the same factory.
@Bean
public KafkaTemplate<String, String> stringTemplate(ProducerFactory<String, String> pf) {
return new KafkaTemplate<>(pf);
}
@Bean
public KafkaTemplate<String, byte[]> bytesTemplate(ProducerFactory<String, byte[]> pf) {
return new KafkaTemplate<>(pf,
Collections.singletonMap(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, ByteArraySerializer.class));
}
Note that a bean of type ProducerFactory<?, ?> (such as the one auto-configured by Spring Boot) can be referenced with different narrowed generic types.
You can also configure the template by using standard <bean/> definitions.
Then, to use the template, you can invoke one of its methods.
When you use the methods with a Message<?> parameter, the topic, partition, and key information is provided in a message header that includes the following items:
-
KafkaHeaders.TOPIC -
KafkaHeaders.PARTITION -
KafkaHeaders.KEY -
KafkaHeaders.TIMESTAMP
The message payload is the data.
Optionally, you can configure the KafkaTemplate with a ProducerListener to get an asynchronous callback with the results of the send (success or failure) instead of waiting for the Future to complete.
The following listing shows the definition of the ProducerListener interface:
public interface ProducerListener<K, V> {
void onSuccess(ProducerRecord<K, V> producerRecord, RecordMetadata recordMetadata);
void onError(ProducerRecord<K, V> producerRecord, RecordMetadata recordMetadata,
Exception exception);
}
By default, the template is configured with a LoggingProducerListener, which logs errors and does nothing when the send is successful.
For convenience, default method implementations are provided in case you want to implement only one of the methods.
Notice that the send methods return a CompletableFuture<SendResult>.
You can register a callback with the listener to receive the result of the send asynchronously.
The following example shows how to do so:
CompletableFuture<SendResult<Integer, String>> future = template.send("myTopic", "something");
future.whenComplete((result, ex) -> {
...
});
SendResult has two properties, a ProducerRecord and RecordMetadata.
See the Kafka API documentation for information about those objects.
The Throwable can be cast to a KafkaProducerException; its failedProducerRecord property contains the failed record.
If you wish to block the sending thread to await the result, you can invoke the future’s get() method; using the method with a timeout is recommended.
If you have set a linger.ms, you may wish to invoke flush() before waiting or, for convenience, the template has a constructor with an autoFlush parameter that causes the template to flush() on each send.
Flushing is only needed if you have set the linger.ms producer property and want to immediately send a partial batch.
Examples
This section shows examples of sending messages to Kafka:
public void sendToKafka(final MyOutputData data) {
final ProducerRecord<String, String> record = createRecord(data);
CompletableFuture<SendResult<Integer, String>> future = template.send(record);
future.whenComplete((result, ex) -> {
if (ex == null) {
handleSuccess(data);
}
else {
handleFailure(data, record, ex);
}
});
}
public void sendToKafka(final MyOutputData data) {
final ProducerRecord<String, String> record = createRecord(data);
try {
template.send(record).get(10, TimeUnit.SECONDS);
handleSuccess(data);
}
catch (ExecutionException e) {
handleFailure(data, record, e.getCause());
}
catch (TimeoutException | InterruptedException e) {
handleFailure(data, record, e);
}
}
Note that the cause of the ExecutionException is KafkaProducerException with the failedProducerRecord property.
Using RoutingKafkaTemplate
Starting with version 2.5, you can use a RoutingKafkaTemplate to select the producer at runtime, based on the destination topic name.
The routing template does not support transactions, execute, flush, or metrics operations because the topic is not known for those operations.
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The template requires a map of java.util.regex.Pattern to ProducerFactory<Object, Object> instances.
This map should be ordered (e.g. a LinkedHashMap) because it is traversed in order; you should add more specific patterns at the beginning.
The following simple Spring Boot application provides an example of how to use the same template to send to different topics, each using a different value serializer.
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Bean
public RoutingKafkaTemplate routingTemplate(GenericApplicationContext context,
ProducerFactory<Object, Object> pf) {
// Clone the PF with a different Serializer, register with Spring for shutdown
Map<String, Object> configs = new HashMap<>(pf.getConfigurationProperties());
configs.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, ByteArraySerializer.class);
DefaultKafkaProducerFactory<Object, Object> bytesPF = new DefaultKafkaProducerFactory<>(configs);
context.registerBean(DefaultKafkaProducerFactory.class, "bytesPF", bytesPF);
Map<Pattern, ProducerFactory<Object, Object>> map = new LinkedHashMap<>();
map.put(Pattern.compile("two"), bytesPF);
map.put(Pattern.compile(".+"), pf); // Default PF with StringSerializer
return new RoutingKafkaTemplate(map);
}
@Bean
public ApplicationRunner runner(RoutingKafkaTemplate routingTemplate) {
return args -> {
routingTemplate.send("one", "thing1");
routingTemplate.send("two", "thing2".getBytes());
};
}
}
The corresponding @KafkaListener s for this example are shown in Annotation Properties.
For another technique to achieve similar results, but with the additional capability of sending different types to the same topic, see Delegating Serializer and Deserializer.
Using DefaultKafkaProducerFactory
As seen in Using KafkaTemplate, a ProducerFactory is used to create the producer.
When not using Transactions, by default, the DefaultKafkaProducerFactory creates a singleton producer used by all clients, as recommended in the KafkaProducer javadocs.
However, if you call flush() on the template, this can cause delays for other threads using the same producer.
Starting with version 2.3, the DefaultKafkaProducerFactory has a new property producerPerThread.
When set to true, the factory will create (and cache) a separate producer for each thread, to avoid this issue.
When producerPerThread is true, user code must call closeThreadBoundProducer() on the factory when the producer is no longer needed.
This will physically close the producer and remove it from the ThreadLocal.
Calling reset() or destroy() will not clean up these producers.
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When creating a DefaultKafkaProducerFactory, key and/or value Serializer classes can be picked up from configuration by calling the constructor that only takes in a Map of properties (see example in Using KafkaTemplate), or Serializer instances may be passed to the DefaultKafkaProducerFactory constructor (in which case all Producer s share the same instances).
Alternatively you can provide Supplier<Serializer> s (starting with version 2.3) that will be used to obtain separate Serializer instances for each Producer:
@Bean
public ProducerFactory<Integer, CustomValue> producerFactory() {
return new DefaultKafkaProducerFactory<>(producerConfigs(), null, () -> new CustomValueSerializer());
}
@Bean
public KafkaTemplate<Integer, CustomValue> kafkaTemplate() {
return new KafkaTemplate<Integer, CustomValue>(producerFactory());
}
Starting with version 2.5.10, you can now update the producer properties after the factory is created.
This might be useful, for example, if you have to update SSL key/trust store locations after a credentials change.
The changes will not affect existing producer instances; call reset() to close any existing producers so that new producers will be created using the new properties.
NOTE: You cannot change a transactional producer factory to non-transactional, and vice-versa.
Two new methods are now provided:
void updateConfigs(Map<String, Object> updates);
void removeConfig(String configKey);
Starting with version 2.8, if you provide serializers as objects (in the constructor or via the setters), the factory will invoke the configure() method to configure them with the configuration properties.
Using ReplyingKafkaTemplate
Version 2.1.3 introduced a subclass of KafkaTemplate to provide request/reply semantics.
The class is named ReplyingKafkaTemplate and has two additional methods; the following shows the method signatures:
RequestReplyFuture<K, V, R> sendAndReceive(ProducerRecord<K, V> record);
RequestReplyFuture<K, V, R> sendAndReceive(ProducerRecord<K, V> record,
Duration replyTimeout);
(Also see Request/Reply with Message<?> s).
The result is a CompletableFuture that is asynchronously populated with the result (or an exception, for a timeout).
The result also has a sendFuture property, which is the result of calling KafkaTemplate.send().
You can use this future to determine the result of the send operation.
In version 3.0, the futures returned by these methods (and their sendFuture properties) have been changed to CompletableFuture s instead of ListenableFuture s.
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If the first method is used, or the replyTimeout argument is null, the template’s defaultReplyTimeout property is used (5 seconds by default).
Starting with version 2.8.8, the template has a new method waitForAssignment.
This is useful if the reply container is configured with auto.offset.reset=latest to avoid sending a request and a reply sent before the container is initialized.
When using manual partition assignment (no group management), the duration for the wait must be greater than the container’s pollTimeout property because the notification will not be sent until after the first poll is completed.
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The following Spring Boot application shows an example of how to use the feature:
@SpringBootApplication
public class KRequestingApplication {
public static void main(String[] args) {
SpringApplication.run(KRequestingApplication.class, args).close();
}
@Bean
public ApplicationRunner runner(ReplyingKafkaTemplate<String, String, String> template) {
return args -> {
if (!template.waitForAssignment(Duration.ofSeconds(10))) {
throw new IllegalStateException("Reply container did not initialize");
}
ProducerRecord<String, String> record = new ProducerRecord<>("kRequests", "foo");
RequestReplyFuture<String, String, String> replyFuture = template.sendAndReceive(record);
SendResult<String, String> sendResult = replyFuture.getSendFuture().get(10, TimeUnit.SECONDS);
System.out.println("Sent ok: " + sendResult.getRecordMetadata());
ConsumerRecord<String, String> consumerRecord = replyFuture.get(10, TimeUnit.SECONDS);
System.out.println("Return value: " + consumerRecord.value());
};
}
@Bean
public ReplyingKafkaTemplate<String, String, String> replyingTemplate(
ProducerFactory<String, String> pf,
ConcurrentMessageListenerContainer<String, String> repliesContainer) {
return new ReplyingKafkaTemplate<>(pf, repliesContainer);
}
@Bean
public ConcurrentMessageListenerContainer<String, String> repliesContainer(
ConcurrentKafkaListenerContainerFactory<String, String> containerFactory) {
ConcurrentMessageListenerContainer<String, String> repliesContainer =
containerFactory.createContainer("kReplies");
repliesContainer.getContainerProperties().setGroupId("repliesGroup");
repliesContainer.setAutoStartup(false);
return repliesContainer;
}
@Bean
public NewTopic kRequests() {
return TopicBuilder.name("kRequests")
.partitions(10)
.replicas(2)
.build();
}
@Bean
public NewTopic kReplies() {
return TopicBuilder.name("kReplies")
.partitions(10)
.replicas(2)
.build();
}
}
Note that we can use Boot’s auto-configured container factory to create the reply container.
If a non-trivial deserializer is being used for replies, consider using an ErrorHandlingDeserializer that delegates to your configured deserializer.
When so configured, the RequestReplyFuture will be completed exceptionally and you can catch the ExecutionException, with the DeserializationException in its cause property.
Starting with version 2.6.7, in addition to detecting DeserializationException s, the template will call the replyErrorChecker function, if provided.
If it returns an exception, the future will be completed exceptionally.
Here is an example:
template.setReplyErrorChecker(record -> {
Header error = record.headers().lastHeader("serverSentAnError");
if (error != null) {
return new MyException(new String(error.value()));
}
else {
return null;
}
});
...
RequestReplyFuture<Integer, String, String> future = template.sendAndReceive(record);
try {
future.getSendFuture().get(10, TimeUnit.SECONDS); // send ok
ConsumerRecord<Integer, String> consumerRecord = future.get(10, TimeUnit.SECONDS);
...
}
catch (InterruptedException e) {
...
}
catch (ExecutionException e) {
if (e.getCause instanceof MyException) {
...
}
}
catch (TimeoutException e) {
...
}
The template sets a header (named KafkaHeaders.CORRELATION_ID by default), which must be echoed back by the server side.
In this case, the following @KafkaListener application responds:
@SpringBootApplication
public class KReplyingApplication {
public static void main(String[] args) {
SpringApplication.run(KReplyingApplication.class, args);
}
@KafkaListener(id="server", topics = "kRequests")
@SendTo // use default replyTo expression
public String listen(String in) {
System.out.println("Server received: " + in);
return in.toUpperCase();
}
@Bean
public NewTopic kRequests() {
return TopicBuilder.name("kRequests")
.partitions(10)
.replicas(2)
.build();
}
@Bean // not required if Jackson is on the classpath
public MessagingMessageConverter simpleMapperConverter() {
MessagingMessageConverter messagingMessageConverter = new MessagingMessageConverter();
messagingMessageConverter.setHeaderMapper(new SimpleKafkaHeaderMapper());
return messagingMessageConverter;
}
}
The @KafkaListener infrastructure echoes the correlation ID and determines the reply topic.
See Forwarding Listener Results using @SendTo for more information about sending replies.
The template uses the default header KafKaHeaders.REPLY_TOPIC to indicate the topic to which the reply goes.
Starting with version 2.2, the template tries to detect the reply topic or partition from the configured reply container.
If the container is configured to listen to a single topic or a single TopicPartitionOffset, it is used to set the reply headers.
If the container is configured otherwise, the user must set up the reply headers.
In this case, an INFO log message is written during initialization.
The following example uses KafkaHeaders.REPLY_TOPIC:
record.headers().add(new RecordHeader(KafkaHeaders.REPLY_TOPIC, "kReplies".getBytes()));
When you configure with a single reply TopicPartitionOffset, you can use the same reply topic for multiple templates, as long as each instance listens on a different partition.
When configuring with a single reply topic, each instance must use a different group.id.
In this case, all instances receive each reply, but only the instance that sent the request finds the correlation ID.
This may be useful for auto-scaling, but with the overhead of additional network traffic and the small cost of discarding each unwanted reply.
When you use this setting, we recommend that you set the template’s sharedReplyTopic to true, which reduces the logging level of unexpected replies to DEBUG instead of the default ERROR.
The following is an example of configuring the reply container to use the same shared reply topic:
@Bean
public ConcurrentMessageListenerContainer<String, String> replyContainer(
ConcurrentKafkaListenerContainerFactory<String, String> containerFactory) {
ConcurrentMessageListenerContainer<String, String> container = containerFactory.createContainer("topic2");
container.getContainerProperties().setGroupId(UUID.randomUUID().toString()); // unique
Properties props = new Properties();
props.setProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "latest"); // so the new group doesn't get old replies
container.getContainerProperties().setKafkaConsumerProperties(props);
return container;
}
If you have multiple client instances and you do not configure them as discussed in the preceding paragraph, each instance needs a dedicated reply topic.
An alternative is to set the KafkaHeaders.REPLY_PARTITION and use a dedicated partition for each instance.
The Header contains a four-byte int (big-endian).
The server must use this header to route the reply to the correct partition (@KafkaListener does this).
In this case, though, the reply container must not use Kafka’s group management feature and must be configured to listen on a fixed partition (by using a TopicPartitionOffset in its ContainerProperties constructor).
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The DefaultKafkaHeaderMapper requires Jackson to be on the classpath (for the @KafkaListener).
If it is not available, the message converter has no header mapper, so you must configure a MessagingMessageConverter with a SimpleKafkaHeaderMapper, as shown earlier.
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By default, 3 headers are used:
-
KafkaHeaders.CORRELATION_ID- used to correlate the reply to a request -
KafkaHeaders.REPLY_TOPIC- used to tell the server where to reply -
KafkaHeaders.REPLY_PARTITION- (optional) used to tell the server which partition to reply to
These header names are used by the @KafkaListener infrastructure to route the reply.
Starting with version 2.3, you can customize the header names - the template has 3 properties correlationHeaderName, replyTopicHeaderName, and replyPartitionHeaderName.
This is useful if your server is not a Spring application (or does not use the @KafkaListener).
Conversely, if the requesting application is not a spring application and puts correlation information in a different header, starting with version 3.0, you can configure a custom correlationHeaderName on the listener container factory and that header will be echoed back.
Previously, the listener had to echo custom correlation headers.
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Request/Reply with Message<?> s
Version 2.7 added methods to the ReplyingKafkaTemplate to send and receive spring-messaging 's Message<?> abstraction:
RequestReplyMessageFuture<K, V> sendAndReceive(Message<?> message);
<P> RequestReplyTypedMessageFuture<K, V, P> sendAndReceive(Message<?> message,
ParameterizedTypeReference<P> returnType);
These will use the template’s default replyTimeout, there are also overloaded versions that can take a timeout in the method call.
In version 3.0, the futures returned by these methods (and their sendFuture properties) have been changed to CompletableFuture s instead of ListenableFuture s.
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Use the first method if the consumer’s Deserializer or the template’s MessageConverter can convert the payload without any additional information, either via configuration or type metadata in the reply message.
Use the second method if you need to provide type information for the return type, to assist the message converter. This also allows the same template to receive different types, even if there is no type metadata in the replies, such as when the server side is not a Spring application. The following is an example of the latter:
@Bean
ReplyingKafkaTemplate<String, String, String> template(
ProducerFactory<String, String> pf,
ConcurrentKafkaListenerContainerFactory<String, String> factory) {
ConcurrentMessageListenerContainer<String, String> replyContainer =
factory.createContainer("replies");
replyContainer.getContainerProperties().setGroupId("request.replies");
ReplyingKafkaTemplate<String, String, String> template =
new ReplyingKafkaTemplate<>(pf, replyContainer);
template.setMessageConverter(new ByteArrayJsonMessageConverter());
template.setDefaultTopic("requests");
return template;
}
@Bean
fun template(
pf: ProducerFactory<String?, String>?,
factory: ConcurrentKafkaListenerContainerFactory<String?, String?>
): ReplyingKafkaTemplate<String?, String, String?> {
val replyContainer = factory.createContainer("replies")
replyContainer.containerProperties.groupId = "request.replies"
val template = ReplyingKafkaTemplate(pf, replyContainer)
template.messageConverter = ByteArrayJsonMessageConverter()
template.defaultTopic = "requests"
return template
}
RequestReplyTypedMessageFuture<String, String, Thing> future1 =
template.sendAndReceive(MessageBuilder.withPayload("getAThing").build(),
new ParameterizedTypeReference<Thing>() { });
log.info(future1.getSendFuture().get(10, TimeUnit.SECONDS).getRecordMetadata().toString());
Thing thing = future1.get(10, TimeUnit.SECONDS).getPayload();
log.info(thing.toString());
RequestReplyTypedMessageFuture<String, String, List<Thing>> future2 =
template.sendAndReceive(MessageBuilder.withPayload("getThings").build(),
new ParameterizedTypeReference<List<Thing>>() { });
log.info(future2.getSendFuture().get(10, TimeUnit.SECONDS).getRecordMetadata().toString());
List<Thing> things = future2.get(10, TimeUnit.SECONDS).getPayload();
things.forEach(thing1 -> log.info(thing1.toString()));
val future1: RequestReplyTypedMessageFuture<String?, String?, Thing?>? =
template.sendAndReceive(MessageBuilder.withPayload("getAThing").build(),
object : ParameterizedTypeReference<Thing?>() {})
log.info(future1?.sendFuture?.get(10, TimeUnit.SECONDS)?.recordMetadata?.toString())
val thing = future1?.get(10, TimeUnit.SECONDS)?.payload
log.info(thing.toString())
val future2: RequestReplyTypedMessageFuture<String?, String?, List<Thing?>?>? =
template.sendAndReceive(MessageBuilder.withPayload("getThings").build(),
object : ParameterizedTypeReference<List<Thing?>?>() {})
log.info(future2?.sendFuture?.get(10, TimeUnit.SECONDS)?.recordMetadata.toString())
val things = future2?.get(10, TimeUnit.SECONDS)?.payload
things?.forEach(Consumer { thing1: Thing? -> log.info(thing1.toString()) })
Reply Type Message<?>
When the @KafkaListener returns a Message<?>, with versions before 2.5, it was necessary to populate the reply topic and correlation id headers.
In this example, we use the reply topic header from the request:
@KafkaListener(id = "requestor", topics = "request")
@SendTo
public Message<?> messageReturn(String in) {
return MessageBuilder.withPayload(in.toUpperCase())
.setHeader(KafkaHeaders.TOPIC, replyTo)
.setHeader(KafkaHeaders.KEY, 42)
.setHeader(KafkaHeaders.CORRELATION_ID, correlation)
.build();
}
This also shows how to set a key on the reply record.
Starting with version 2.5, the framework will detect if these headers are missing and populate them with the topic - either the topic determined from the @SendTo value or the incoming KafkaHeaders.REPLY_TOPIC header (if present).
It will also echo the incoming KafkaHeaders.CORRELATION_ID and KafkaHeaders.REPLY_PARTITION, if present.
@KafkaListener(id = "requestor", topics = "request")
@SendTo // default REPLY_TOPIC header
public Message<?> messageReturn(String in) {
return MessageBuilder.withPayload(in.toUpperCase())
.setHeader(KafkaHeaders.KEY, 42)
.build();
}
Aggregating Multiple Replies
The template in Using ReplyingKafkaTemplate is strictly for a single request/reply scenario.
For cases where multiple receivers of a single message return a reply, you can use the AggregatingReplyingKafkaTemplate.
This is an implementation of the client-side of the Scatter-Gather Enterprise Integration Pattern.
Like the ReplyingKafkaTemplate, the AggregatingReplyingKafkaTemplate constructor takes a producer factory and a listener container to receive the replies; it has a third parameter BiPredicate<List<ConsumerRecord<K, R>>, Boolean> releaseStrategy which is consulted each time a reply is received; when the predicate returns true, the collection of ConsumerRecord s is used to complete the Future returned by the sendAndReceive method.
There is an additional property returnPartialOnTimeout (default false).
When this is set to true, instead of completing the future with a KafkaReplyTimeoutException, a partial result completes the future normally (as long as at least one reply record has been received).
Starting with version 2.3.5, the predicate is also called after a timeout (if returnPartialOnTimeout is true).
The first argument is the current list of records; the second is true if this call is due to a timeout.
The predicate can modify the list of records.
AggregatingReplyingKafkaTemplate<Integer, String, String> template =
new AggregatingReplyingKafkaTemplate<>(producerFactory, container,
coll -> coll.size() == releaseSize);
...
RequestReplyFuture<Integer, String, Collection<ConsumerRecord<Integer, String>>> future =
template.sendAndReceive(record);
future.getSendFuture().get(10, TimeUnit.SECONDS); // send ok
ConsumerRecord<Integer, Collection<ConsumerRecord<Integer, String>>> consumerRecord =
future.get(30, TimeUnit.SECONDS);
Notice that the return type is a ConsumerRecord with a value that is a collection of ConsumerRecord s.
The "outer" ConsumerRecord is not a "real" record, it is synthesized by the template, as a holder for the actual reply records received for the request.
When a normal release occurs (release strategy returns true), the topic is set to aggregatedResults; if returnPartialOnTimeout is true, and timeout occurs (and at least one reply record has been received), the topic is set to partialResultsAfterTimeout.
The template provides constant static variables for these "topic" names:
/**
* Pseudo topic name for the "outer" {@link ConsumerRecords} that has the aggregated
* results in its value after a normal release by the release strategy.
*/
public static final String AGGREGATED_RESULTS_TOPIC = "aggregatedResults";
/**
* Pseudo topic name for the "outer" {@link ConsumerRecords} that has the aggregated
* results in its value after a timeout.
*/
public static final String PARTIAL_RESULTS_AFTER_TIMEOUT_TOPIC = "partialResultsAfterTimeout";
The real ConsumerRecord s in the Collection contain the actual topic(s) from which the replies are received.
The listener container for the replies MUST be configured with AckMode.MANUAL or AckMode.MANUAL_IMMEDIATE; the consumer property enable.auto.commit must be false (the default since version 2.3).
To avoid any possibility of losing messages, the template only commits offsets when there are zero requests outstanding, i.e. when the last outstanding request is released by the release strategy.
After a rebalance, it is possible for duplicate reply deliveries; these will be ignored for any in-flight requests; you may see error log messages when duplicate replies are received for already released replies.
|
If you use an ErrorHandlingDeserializer with this aggregating template, the framework will not automatically detect DeserializationException s.
Instead, the record (with a null value) will be returned intact, with the deserialization exception(s) in headers.
It is recommended that applications call the utility method ReplyingKafkaTemplate.checkDeserialization() method to determine if a deserialization exception occurred.
See its javadocs for more information.
The replyErrorChecker is also not called for this aggregating template; you should perform the checks on each element of the reply.
|
4.1.4. Receiving Messages
You can receive messages by configuring a MessageListenerContainer and providing a message listener or by using the @KafkaListener annotation.
Message Listeners
When you use a message listener container, you must provide a listener to receive data. There are currently eight supported interfaces for message listeners. The following listing shows these interfaces:
public interface MessageListener<K, V> { (1)
void onMessage(ConsumerRecord<K, V> data);
}
public interface AcknowledgingMessageListener<K, V> { (2)
void onMessage(ConsumerRecord<K, V> data, Acknowledgment acknowledgment);
}
public interface ConsumerAwareMessageListener<K, V> extends MessageListener<K, V> { (3)
void onMessage(ConsumerRecord<K, V> data, Consumer<?, ?> consumer);
}
public interface AcknowledgingConsumerAwareMessageListener<K, V> extends MessageListener<K, V> { (4)
void onMessage(ConsumerRecord<K, V> data, Acknowledgment acknowledgment, Consumer<?, ?> consumer);
}
public interface BatchMessageListener<K, V> { (5)
void onMessage(List<ConsumerRecord<K, V>> data);
}
public interface BatchAcknowledgingMessageListener<K, V> { (6)
void onMessage(List<ConsumerRecord<K, V>> data, Acknowledgment acknowledgment);
}
public interface BatchConsumerAwareMessageListener<K, V> extends BatchMessageListener<K, V> { (7)
void onMessage(List<ConsumerRecord<K, V>> data, Consumer<?, ?> consumer);
}
public interface BatchAcknowledgingConsumerAwareMessageListener<K, V> extends BatchMessageListener<K, V> { (8)
void onMessage(List<ConsumerRecord<K, V>> data, Acknowledgment acknowledgment, Consumer<?, ?> consumer);
}
| 1 | Use this interface for processing individual ConsumerRecord instances received from the Kafka consumer poll() operation when using auto-commit or one of the container-managed commit methods. |
| 2 | Use this interface for processing individual ConsumerRecord instances received from the Kafka consumer poll() operation when using one of the manual commit methods. |
| 3 | Use this interface for processing individual ConsumerRecord instances received from the Kafka consumer poll() operation when using auto-commit or one of the container-managed commit methods.
Access to the Consumer object is provided. |
| 4 | Use this interface for processing individual ConsumerRecord instances received from the Kafka consumer poll() operation when using one of the manual commit methods.
Access to the Consumer object is provided. |
| 5 | Use this interface for processing all ConsumerRecord instances received from the Kafka consumer poll() operation when using auto-commit or one of the container-managed commit methods.
AckMode.RECORD is not supported when you use this interface, since the listener is given the complete batch. |
| 6 | Use this interface for processing all ConsumerRecord instances received from the Kafka consumer poll() operation when using one of the manual commit methods. |
| 7 | Use this interface for processing all ConsumerRecord instances received from the Kafka consumer poll() operation when using auto-commit or one of the container-managed commit methods.
AckMode.RECORD is not supported when you use this interface, since the listener is given the complete batch.
Access to the Consumer object is provided. |
| 8 | Use this interface for processing all ConsumerRecord instances received from the Kafka consumer poll() operation when using one of the manual commit methods.
Access to the Consumer object is provided. |
The Consumer object is not thread-safe.
You must only invoke its methods on the thread that calls the listener.
|
You should not execute any Consumer<?, ?> methods that affect the consumer’s positions and or committed offsets in your listener; the container needs to manage such information.
|
Message Listener Containers
Two MessageListenerContainer implementations are provided:
-
KafkaMessageListenerContainer -
ConcurrentMessageListenerContainer
The KafkaMessageListenerContainer receives all message from all topics or partitions on a single thread.
The ConcurrentMessageListenerContainer delegates to one or more KafkaMessageListenerContainer instances to provide multi-threaded consumption.
Starting with version 2.2.7, you can add a RecordInterceptor to the listener container; it will be invoked before calling the listener allowing inspection or modification of the record.
If the interceptor returns null, the listener is not called.
Starting with version 2.7, it has additional methods which are called after the listener exits (normally, or by throwing an exception).
Also, starting with version 2.7, there is now a BatchInterceptor, providing similar functionality for Batch Listeners.
In addition, the ConsumerAwareRecordInterceptor (and BatchInterceptor) provide access to the Consumer<?, ?>.
This might be used, for example, to access the consumer metrics in the interceptor.
| You should not execute any methods that affect the consumer’s positions and or committed offsets in these interceptors; the container needs to manage such information. |
If the interceptor mutates the record (by creating a new one), the topic, partition, and offset must remain the same to avoid unexpected side effects such as record loss.
|
The CompositeRecordInterceptor and CompositeBatchInterceptor can be used to invoke multiple interceptors.
By default, starting with version 2.8, when using transactions, the interceptor is invoked before the transaction has started.
You can set the listener container’s interceptBeforeTx property to false to invoke the interceptor after the transaction has started instead.
Starting with version 2.9, this will apply to any transaction manager, not just KafkaAwareTransactionManager s.
This allows, for example, the interceptor to participate in a JDBC transaction started by the container.
Starting with versions 2.3.8, 2.4.6, the ConcurrentMessageListenerContainer now supports Static Membership when the concurrency is greater than one.
The group.instance.id is suffixed with -n with n starting at 1.
This, together with an increased session.timeout.ms, can be used to reduce rebalance events, for example, when application instances are restarted.
Using KafkaMessageListenerContainer
The following constructor is available:
public KafkaMessageListenerContainer(ConsumerFactory<K, V> consumerFactory,
ContainerProperties containerProperties)
It receives a ConsumerFactory and information about topics and partitions, as well as other configuration, in a ContainerProperties
object.
ContainerProperties has the following constructors:
public ContainerProperties(TopicPartitionOffset... topicPartitions)
public ContainerProperties(String... topics)
public ContainerProperties(Pattern topicPattern)
The first constructor takes an array of TopicPartitionOffset arguments to explicitly instruct the container about which partitions to use (using the consumer assign() method) and with an optional initial offset.
A positive value is an absolute offset by default.
A negative value is relative to the current last offset within a partition by default.
A constructor for TopicPartitionOffset that takes an additional boolean argument is provided.
If this is true, the initial offsets (positive or negative) are relative to the current position for this consumer.
The offsets are applied when the container is started.
The second takes an array of topics, and Kafka allocates the partitions based on the group.id property — distributing partitions across the group.
The third uses a regex Pattern to select the topics.
To assign a MessageListener to a container, you can use the ContainerProps.setMessageListener method when creating the Container.
The following example shows how to do so:
ContainerProperties containerProps = new ContainerProperties("topic1", "topic2");
containerProps.setMessageListener(new MessageListener<Integer, String>() {
...
});
DefaultKafkaConsumerFactory<Integer, String> cf =
new DefaultKafkaConsumerFactory<>(consumerProps());
KafkaMessageListenerContainer<Integer, String> container =
new KafkaMessageListenerContainer<>(cf, containerProps);
return container;
Note that when creating a DefaultKafkaConsumerFactory, using the constructor that just takes in the properties as above means that key and value Deserializer classes are picked up from configuration.
Alternatively, Deserializer instances may be passed to the DefaultKafkaConsumerFactory constructor for key and/or value, in which case all Consumers share the same instances.
Another option is to provide Supplier<Deserializer> s (starting with version 2.3) that will be used to obtain separate Deserializer instances for each Consumer:
DefaultKafkaConsumerFactory<Integer, CustomValue> cf =
new DefaultKafkaConsumerFactory<>(consumerProps(), null, () -> new CustomValueDeserializer());
KafkaMessageListenerContainer<Integer, String> container =
new KafkaMessageListenerContainer<>(cf, containerProps);
return container;
Refer to the Javadoc for ContainerProperties for more information about the various properties that you can set.
Since version 2.1.1, a new property called logContainerConfig is available.
When true and INFO logging is enabled each listener container writes a log message summarizing its configuration properties.
By default, logging of topic offset commits is performed at the DEBUG logging level.
Starting with version 2.1.2, a property in ContainerProperties called commitLogLevel lets you specify the log level for these messages.
For example, to change the log level to INFO, you can use containerProperties.setCommitLogLevel(LogIfLevelEnabled.Level.INFO);.
Starting with version 2.2, a new container property called missingTopicsFatal has been added (default: false since 2.3.4).
This prevents the container from starting if any of the configured topics are not present on the broker.
It does not apply if the container is configured to listen to a topic pattern (regex).
Previously, the container threads looped within the consumer.poll() method waiting for the topic to appear while logging many messages.
Aside from the logs, there was no indication that there was a problem.
As of version 2.8, a new container property authExceptionRetryInterval has been introduced.
This causes the container to retry fetching messages after getting any AuthenticationException or AuthorizationException from the KafkaConsumer.
This can happen when, for example, the configured user is denied access to read a certain topic or credentials are incorrect.
Defining authExceptionRetryInterval allows the container to recover when proper permissions are granted.
| By default, no interval is configured - authentication and authorization errors are considered fatal, which causes the container to stop. |
Starting with version 2.8, when creating the consumer factory, if you provide deserializers as objects (in the constructor or via the setters), the factory will invoke the configure() method to configure them with the configuration properties.
Using ConcurrentMessageListenerContainer
The single constructor is similar to the KafkaListenerContainer constructor.
The following listing shows the constructor’s signature:
public ConcurrentMessageListenerContainer(ConsumerFactory<K, V> consumerFactory,
ContainerProperties containerProperties)
It also has a concurrency property.
For example, container.setConcurrency(3) creates three KafkaMessageListenerContainer instances.
For the first constructor, Kafka distributes the partitions across the consumers using its group management capabilities.
|
When listening to multiple topics, the default partition distribution may not be what you expect.
For example, if you have three topics with five partitions each and you want to use When using Spring Boot, you can assign set the strategy as follows: |
When the container properties are configured with TopicPartitionOffset s, the ConcurrentMessageListenerContainer distributes the TopicPartitionOffset instances across the delegate KafkaMessageListenerContainer instances.
If, say, six TopicPartitionOffset instances are provided and the concurrency is 3; each container gets two partitions.
For five TopicPartitionOffset instances, two containers get two partitions, and the third gets one.
If the concurrency is greater than the number of TopicPartitions, the concurrency is adjusted down such that each container gets one partition.
The client.id property (if set) is appended with -n where n is the consumer instance that corresponds to the concurrency.
This is required to provide unique names for MBeans when JMX is enabled.
|
Starting with version 1.3, the MessageListenerContainer provides access to the metrics of the underlying KafkaConsumer.
In the case of ConcurrentMessageListenerContainer, the metrics() method returns the metrics for all the target KafkaMessageListenerContainer instances.
The metrics are grouped into the Map<MetricName, ? extends Metric> by the client-id provided for the underlying KafkaConsumer.
Starting with version 2.3, the ContainerProperties provides an idleBetweenPolls option to let the main loop in the listener container to sleep between KafkaConsumer.poll() calls.
An actual sleep interval is selected as the minimum from the provided option and difference between the max.poll.interval.ms consumer config and the current records batch processing time.
Committing Offsets
Several options are provided for committing offsets.
If the enable.auto.commit consumer property is true, Kafka auto-commits the offsets according to its configuration.
If it is false, the containers support several AckMode settings (described in the next list).
The default AckMode is BATCH.
Starting with version 2.3, the framework sets enable.auto.commit to false unless explicitly set in the configuration.
Previously, the Kafka default (true) was used if the property was not set.
The consumer poll() method returns one or more ConsumerRecords.
The MessageListener is called for each record.
The following lists describes the action taken by the container for each AckMode (when transactions are not being used):
-
RECORD: Commit the offset when the listener returns after processing the record. -
BATCH: Commit the offset when all the records returned by thepoll()have been processed. -
TIME: Commit the offset when all the records returned by thepoll()have been processed, as long as theackTimesince the last commit has been exceeded. -
COUNT: Commit the offset when all the records returned by thepoll()have been processed, as long asackCountrecords have been received since the last commit. -
COUNT_TIME: Similar toTIMEandCOUNT, but the commit is performed if either condition istrue. -
MANUAL: The message listener is responsible toacknowledge()theAcknowledgment. After that, the same semantics asBATCHare applied. -
MANUAL_IMMEDIATE: Commit the offset immediately when theAcknowledgment.acknowledge()method is called by the listener.
When using transactions, the offset(s) are sent to the transaction and the semantics are equivalent to RECORD or BATCH, depending on the listener type (record or batch).
MANUAL, and MANUAL_IMMEDIATE require the listener to be an AcknowledgingMessageListener or a BatchAcknowledgingMessageListener.
See Message Listeners.
|
Depending on the syncCommits container property, the commitSync() or commitAsync() method on the consumer is used.
syncCommits is true by default; also see setSyncCommitTimeout.
See setCommitCallback to get the results of asynchronous commits; the default callback is the LoggingCommitCallback which logs errors (and successes at debug level).
Because the listener container has it’s own mechanism for committing offsets, it prefers the Kafka ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG to be false.
Starting with version 2.3, it unconditionally sets it to false unless specifically set in the consumer factory or the container’s consumer property overrides.
The Acknowledgment has the following method:
public interface Acknowledgment {
void acknowledge();
}
This method gives the listener control over when offsets are committed.
Starting with version 2.3, the Acknowledgment interface has two additional methods nack(long sleep) and nack(int index, long sleep).
The first one is used with a record listener, the second with a batch listener.
Calling the wrong method for your listener type will throw an IllegalStateException.
If you want to commit a partial batch, using nack(), When using transactions, set the AckMode to MANUAL; invoking nack() will send the offsets of the successfully processed records to the transaction.
|
nack() can only be called on the consumer thread that invokes your listener.
|
nack() is not allowed when using Out of Order Commits.
|
With a record listener, when nack() is called, any pending offsets are committed, the remaining records from the last poll are discarded, and seeks are performed on their partitions so that the failed record and unprocessed records are redelivered on the next poll().
The consumer can be paused before redelivery, by setting the sleep argument.
This is similar functionality to throwing an exception when the container is configured with a DefaultErrorHandler.
When using a batch listener, you can specify the index within the batch where the failure occurred.
When nack() is called, offsets will be committed for records before the index and seeks are performed on the partitions for the failed and discarded records so that they will be redelivered on the next poll().
See Container Error Handlers for more information.
The consumer is paused during the sleep so that we continue to poll the broker to keep the consumer alive.
The actual sleep time, and its resolution, depends on the container’s pollTimeout which defaults to 5 seconds.
The minimum sleep time is equal to the pollTimeout and all sleep times will be a multiple of it.
For small sleep times or, to increase its accuracy, consider reducing the container’s pollTimeout.
|
Starting with version 3.0.10, batch listeners can commit the offsets of parts of the batch, using acknowledge(index) on the Acknowledgment argument.
When this method is called, the offset of the record at the index (as well as all previous records) will be committed.
Calling acknowledge() after a partial batch commit is performed will commit the offsets of the remainder of the batch.
The following limitations apply:
-
AckMode.MANUAL_IMMEDIATEis required -
The method must be called on the listener thread
-
The listener must consume a
Listrather than the rawConsumerRecords -
The index must be in the range of the list’s elements
-
The index must be larger than that used in a previous call
These restrictions are enforced and the method will throw an IllegalArgumentException or IllegalStateException, depending on the violation.
Listener Container Auto Startup
The listener containers implement SmartLifecycle, and autoStartup is true by default.
The containers are started in a late phase (Integer.MAX-VALUE - 100).
Other components that implement SmartLifecycle, to handle data from listeners, should be started in an earlier phase.
The - 100 leaves room for later phases to enable components to be auto-started after the containers.
Manually Committing Offsets
Normally, when using AckMode.MANUAL or AckMode.MANUAL_IMMEDIATE, the acknowledgments must be acknowledged in order, because Kafka does not maintain state for each record, only a committed offset for each group/partition.
Starting with version 2.8, you can now set the container property asyncAcks, which allows the acknowledgments for records returned by the poll to be acknowledged in any order.
The listener container will defer the out-of-order commits until the missing acknowledgments are received.
The consumer will be paused (no new records delivered) until all the offsets for the previous poll have been committed.
| While this feature allows applications to process records asynchronously, it should be understood that it increases the possibility of duplicate deliveries after a failure. |
@KafkaListener Annotation
The @KafkaListener annotation is used to designate a bean method as a listener for a listener container.
The bean is wrapped in a MessagingMessageListenerAdapter configured with various features, such as converters to convert the data, if necessary, to match the method parameters.
You can configure most attributes on the annotation with SpEL by using #{…} or property placeholders (${…}).
See the Javadoc for more information.
Record Listeners
The @KafkaListener annotation provides a mechanism for simple POJO listeners.
The following example shows how to use it:
public class Listener {
@KafkaListener(id = "foo", topics = "myTopic", clientIdPrefix = "myClientId")
public void listen(String data) {
...
}
}
This mechanism requires an @EnableKafka annotation on one of your @Configuration classes and a listener container factory, which is used to configure the underlying ConcurrentMessageListenerContainer.
By default, a bean with name kafkaListenerContainerFactory is expected.
The following example shows how to use ConcurrentMessageListenerContainer:
@Configuration
@EnableKafka
public class KafkaConfig {
@Bean
KafkaListenerContainerFactory<ConcurrentMessageListenerContainer<Integer, String>>
kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setConcurrency(3);
factory.getContainerProperties().setPollTimeout(3000);
return factory;
}
@Bean
public ConsumerFactory<Integer, String> consumerFactory() {
return new DefaultKafkaConsumerFactory<>(consumerConfigs());
}
@Bean
public Map<String, Object> consumerConfigs() {
Map<String, Object> props = new HashMap<>();
props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, embeddedKafka.getBrokersAsString());
...
return props;
}
}
Notice that, to set container properties, you must use the getContainerProperties() method on the factory.
It is used as a template for the actual properties injected into the container.
Starting with version 2.1.1, you can now set the client.id property for consumers created by the annotation.
The clientIdPrefix is suffixed with -n, where n is an integer representing the container number when using concurrency.
Starting with version 2.2, you can now override the container factory’s concurrency and autoStartup properties by using properties on the annotation itself.
The properties can be simple values, property placeholders, or SpEL expressions.
The following example shows how to do so:
@KafkaListener(id = "myListener", topics = "myTopic",
autoStartup = "${listen.auto.start:true}", concurrency = "${listen.concurrency:3}")
public void listen(String data) {
...
}
Explicit Partition Assignment
You can also configure POJO listeners with explicit topics and partitions (and, optionally, their initial offsets). The following example shows how to do so:
@KafkaListener(id = "thing2", topicPartitions =
{ @TopicPartition(topic = "topic1", partitions = { "0", "1" }),
@TopicPartition(topic = "topic2", partitions = "0",
partitionOffsets = @PartitionOffset(partition = "1", initialOffset = "100"))
})
public void listen(ConsumerRecord<?, ?> record) {
...
}
You can specify each partition in the partitions or partitionOffsets attribute but not both.
As with most annotation properties, you can use SpEL expressions; for an example of how to generate a large list of partitions, see Manually Assigning All Partitions.
Starting with version 2.5.5, you can apply an initial offset to all assigned partitions:
@KafkaListener(id = "thing3", topicPartitions =
{ @TopicPartition(topic = "topic1", partitions = { "0", "1" },
partitionOffsets = @PartitionOffset(partition = "*", initialOffset = "0"))
})
public void listen(ConsumerRecord<?, ?> record) {
...
}
The * wildcard represents all partitions in the partitions attribute.
There must only be one @PartitionOffset with the wildcard in each @TopicPartition.
In addition, when the listener implements ConsumerSeekAware, onPartitionsAssigned is now called, even when using manual assignment.
This allows, for example, any arbitrary seek operations at that time.
Starting with version 2.6.4, you can specify a comma-delimited list of partitions, or partition ranges:
@KafkaListener(id = "pp", autoStartup = "false",
topicPartitions = @TopicPartition(topic = "topic1",
partitions = "0-5, 7, 10-15"))
public void process(String in) {
...
}
The range is inclusive; the example above will assign partitions 0, 1, 2, 3, 4, 5, 7, 10, 11, 12, 13, 14, 15.
The same technique can be used when specifying initial offsets:
@KafkaListener(id = "thing3", topicPartitions =
{ @TopicPartition(topic = "topic1",
partitionOffsets = @PartitionOffset(partition = "0-5", initialOffset = "0"))
})
public void listen(ConsumerRecord<?, ?> record) {
...
}
The initial offset will be applied to all 6 partitions.
Manual Acknowledgment
When using manual AckMode, you can also provide the listener with the Acknowledgment.
The following example also shows how to use a different container factory.
@KafkaListener(id = "cat", topics = "myTopic",
containerFactory = "kafkaManualAckListenerContainerFactory")
public void listen(String data, Acknowledgment ack) {
...
ack.acknowledge();
}
Consumer Record Metadata
Finally, metadata about the record is available from message headers. You can use the following header names to retrieve the headers of the message:
-
KafkaHeaders.OFFSET -
KafkaHeaders.RECEIVED_KEY -
KafkaHeaders.RECEIVED_TOPIC -
KafkaHeaders.RECEIVED_PARTITION -
KafkaHeaders.RECEIVED_TIMESTAMP -
KafkaHeaders.TIMESTAMP_TYPE
Starting with version 2.5 the RECEIVED_KEY is not present if the incoming record has a null key; previously the header was populated with a null value.
This change is to make the framework consistent with spring-messaging conventions where null valued headers are not present.
The following example shows how to use the headers:
@KafkaListener(id = "qux", topicPattern = "myTopic1")
public void listen(@Payload String foo,
@Header(name = KafkaHeaders.RECEIVED_KEY, required = false) Integer key,
@Header(KafkaHeaders.RECEIVED_PARTITION) int partition,
@Header(KafkaHeaders.RECEIVED_TOPIC) String topic,
@Header(KafkaHeaders.RECEIVED_TIMESTAMP) long ts
) {
...
}
Parameter annotations (@Payload, @Header) must be specified on the concrete implementation of the listener method; they will not be detected if they are defined on an interface.
|
Starting with version 2.5, instead of using discrete headers, you can receive record metadata in a ConsumerRecordMetadata parameter.
@KafkaListener(...)
public void listen(String str, ConsumerRecordMetadata meta) {
...
}
This contains all the data from the ConsumerRecord except the key and value.
Batch Listeners
Starting with version 1.1, you can configure @KafkaListener methods to receive the entire batch of consumer records received from the consumer poll.
| Non-Blocking Retries are not supported with batch listeners. |
To configure the listener container factory to create batch listeners, you can set the batchListener property.
The following example shows how to do so:
@Bean
public KafkaListenerContainerFactory<?> batchFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setBatchListener(true); // <<<<<<<<<<<<<<<<<<<<<<<<<
return factory;
}
Starting with version 2.8, you can override the factory’s batchListener propery using the batch property on the @KafkaListener annotation.
This, together with the changes to Container Error Handlers allows the same factory to be used for both record and batch listeners.
|
Starting with version 2.9.6, the container factory has separate setters for the recordMessageConverter and batchMessageConverter properties.
Previously, there was only one property messageConverter which applied to both record and batch listeners.
|
The following example shows how to receive a list of payloads:
@KafkaListener(id = "list", topics = "myTopic", containerFactory = "batchFactory")
public void listen(List<String> list) {
...
}
The topic, partition, offset, and so on are available in headers that parallel the payloads. The following example shows how to use the headers:
@KafkaListener(id = "list", topics = "myTopic", containerFactory = "batchFactory")
public void listen(List<String> list,
@Header(KafkaHeaders.RECEIVED_KEY) List<Integer> keys,
@Header(KafkaHeaders.RECEIVED_PARTITION) List<Integer> partitions,
@Header(KafkaHeaders.RECEIVED_TOPIC) List<String> topics,
@Header(KafkaHeaders.OFFSET) List<Long> offsets) {
...
}
Alternatively, you can receive a List of Message<?> objects with each offset and other details in each message, but it must be the only parameter (aside from optional Acknowledgment, when using manual commits, and/or Consumer<?, ?> parameters) defined on the method.
The following example shows how to do so:
@KafkaListener(id = "listMsg", topics = "myTopic", containerFactory = "batchFactory")
public void listen14(List<Message<?>> list) {
...
}
@KafkaListener(id = "listMsgAck", topics = "myTopic", containerFactory = "batchFactory")
public void listen15(List<Message<?>> list, Acknowledgment ack) {
...
}
@KafkaListener(id = "listMsgAckConsumer", topics = "myTopic", containerFactory = "batchFactory")
public void listen16(List<Message<?>> list, Acknowledgment ack, Consumer<?, ?> consumer) {
...
}
No conversion is performed on the payloads in this case.
If the BatchMessagingMessageConverter is configured with a RecordMessageConverter, you can also add a generic type to the Message parameter and the payloads are converted.
See Payload Conversion with Batch Listeners for more information.
You can also receive a list of ConsumerRecord<?, ?> objects, but it must be the only parameter (aside from optional Acknowledgment, when using manual commits and Consumer<?, ?> parameters) defined on the method.
The following example shows how to do so:
@KafkaListener(id = "listCRs", topics = "myTopic", containerFactory = "batchFactory")
public void listen(List<ConsumerRecord<Integer, String>> list) {
...
}
@KafkaListener(id = "listCRsAck", topics = "myTopic", containerFactory = "batchFactory")
public void listen(List<ConsumerRecord<Integer, String>> list, Acknowledgment ack) {
...
}
Starting with version 2.2, the listener can receive the complete ConsumerRecords<?, ?> object returned by the poll() method, letting the listener access additional methods, such as partitions() (which returns the TopicPartition instances in the list) and records(TopicPartition) (which gets selective records).
Again, this must be the only parameter (aside from optional Acknowledgment, when using manual commits or Consumer<?, ?> parameters) on the method.
The following example shows how to do so:
@KafkaListener(id = "pollResults", topics = "myTopic", containerFactory = "batchFactory")
public void pollResults(ConsumerRecords<?, ?> records) {
...
}
If the container factory has a RecordFilterStrategy configured, it is ignored for ConsumerRecords<?, ?> listeners, with a WARN log message emitted.
Records can only be filtered with a batch listener if the <List<?>> form of listener is used.
By default, records are filtered one-at-a-time; starting with version 2.8, you can override filterBatch to filter the entire batch in one call.
|
Annotation Properties
Starting with version 2.0, the id property (if present) is used as the Kafka consumer group.id property, overriding the configured property in the consumer factory, if present.
You can also set groupId explicitly or set idIsGroup to false to restore the previous behavior of using the consumer factory group.id.
You can use property placeholders or SpEL expressions within most annotation properties, as the following example shows:
@KafkaListener(topics = "${some.property}")
@KafkaListener(topics = "#{someBean.someProperty}",
groupId = "#{someBean.someProperty}.group")
Starting with version 2.1.2, the SpEL expressions support a special token: __listener.
It is a pseudo bean name that represents the current bean instance within which this annotation exists.
Consider the following example:
@Bean
public Listener listener1() {
return new Listener("topic1");
}
@Bean
public Listener listener2() {
return new Listener("topic2");
}
Given the beans in the previous example, we can then use the following:
public class Listener {
private final String topic;
public Listener(String topic) {
this.topic = topic;
}
@KafkaListener(topics = "#{__listener.topic}",
groupId = "#{__listener.topic}.group")
public void listen(...) {
...
}
public String getTopic() {
return this.topic;
}
}
If, in the unlikely event that you have an actual bean called __listener, you can change the expression token byusing the beanRef attribute.
The following example shows how to do so:
@KafkaListener(beanRef = "__x", topics = "#{__x.topic}",
groupId = "#{__x.topic}.group")
Starting with version 2.2.4, you can specify Kafka consumer properties directly on the annotation, these will override any properties with the same name configured in the consumer factory. You cannot specify the group.id and client.id properties this way; they will be ignored; use the groupId and clientIdPrefix annotation properties for those.
The properties are specified as individual strings with the normal Java Properties file format: foo:bar, foo=bar, or foo bar.
@KafkaListener(topics = "myTopic", groupId = "group", properties = {
"max.poll.interval.ms:60000",
ConsumerConfig.MAX_POLL_RECORDS_CONFIG + "=100"
})
The following is an example of the corresponding listeners for the example in Using RoutingKafkaTemplate.
@KafkaListener(id = "one", topics = "one")
public void listen1(String in) {
System.out.println("1: " + in);
}
@KafkaListener(id = "two", topics = "two",
properties = "value.deserializer:org.apache.kafka.common.serialization.ByteArrayDeserializer")
public void listen2(byte[] in) {
System.out.println("2: " + new String(in));
}
Obtaining the Consumer group.id
When running the same listener code in multiple containers, it may be useful to be able to determine which container (identified by its group.id consumer property) that a record came from.
You can call KafkaUtils.getConsumerGroupId() on the listener thread to do this.
Alternatively, you can access the group id in a method parameter.
@KafkaListener(id = "bar", topicPattern = "${topicTwo:annotated2}", exposeGroupId = "${always:true}")
public void listener(@Payload String foo,
@Header(KafkaHeaders.GROUP_ID) String groupId) {
...
}
This is available in record listeners and batch listeners that receive a List<?> of records.
It is not available in a batch listener that receives a ConsumerRecords<?, ?> argument.
Use the KafkaUtils mechanism in that case.
|
Container Thread Naming
A TaskExecutor is used to invoke the consumer and the listener.
You can provide a custom executor by setting the consumerExecutor property of the container’s ContainerProperties.
When using pooled executors, be sure that enough threads are available to handle the concurrency across all the containers in which they are used.
When using the ConcurrentMessageListenerContainer, a thread from the executor is used for each consumer (concurrency).
If you do not provide a consumer executor, a SimpleAsyncTaskExecutor is used for each container.
This executor creates threads with names similar to <beanName>-C-<n>.
For the ConcurrentMessageListenerContainer, the <beanName> part of the thread name becomes <beanName>-m, where m represents the consumer instance.
n increments each time the container is started.
So, with a bean name of container, threads in this container will be named container-0-C-1, container-1-C-1 etc., after the container is started the first time; container-0-C-2, container-1-C-2 etc., after a stop and subsequent start.
Starting with version 3.0.1, you can now change the name of the thread, regardless of which executor is used.
Set the AbstractMessageListenerContainer.changeConsumerThreadName property to true and the AbstractMessageListenerContainer.threadNameSupplier will be invoked to obtain the thread name.
This is a Function<MessageListenerContainer, String>, with the default implementation returning container.getListenerId().
@KafkaListener as a Meta Annotation
Starting with version 2.2, you can now use @KafkaListener as a meta annotation.
The following example shows how to do so:
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@KafkaListener
public @interface MyThreeConsumersListener {
@AliasFor(annotation = KafkaListener.class, attribute = "id")
String id();
@AliasFor(annotation = KafkaListener.class, attribute = "topics")
String[] topics();
@AliasFor(annotation = KafkaListener.class, attribute = "concurrency")
String concurrency() default "3";
}
You must alias at least one of topics, topicPattern, or topicPartitions (and, usually, id or groupId unless you have specified a group.id in the consumer factory configuration).
The following example shows how to do so:
@MyThreeConsumersListener(id = "my.group", topics = "my.topic")
public void listen1(String in) {
...
}
@KafkaListener on a Class
When you use @KafkaListener at the class-level, you must specify @KafkaHandler at the method level.
When messages are delivered, the converted message payload type is used to determine which method to call.
The following example shows how to do so:
@KafkaListener(id = "multi", topics = "myTopic")
static class MultiListenerBean {
@KafkaHandler
public void listen(String foo) {
...
}
@KafkaHandler
public void listen(Integer bar) {
...
}
@KafkaHandler(isDefault = true)
public void listenDefault(Object object) {
...
}
}
Starting with version 2.1.3, you can designate a @KafkaHandler method as the default method that is invoked if there is no match on other methods.
At most, one method can be so designated.
When using @KafkaHandler methods, the payload must have already been converted to the domain object (so the match can be performed).
Use a custom deserializer, the JsonDeserializer, or the JsonMessageConverter with its TypePrecedence set to TYPE_ID.
See Serialization, Deserialization, and Message Conversion for more information.
Due to some limitations in the way Spring resolves method arguments, a default @KafkaHandler cannot receive discrete headers; it must use the ConsumerRecordMetadata as discussed in Consumer Record Metadata.
|
For example:
@KafkaHandler(isDefault = true)
public void listenDefault(Object object, @Header(KafkaHeaders.RECEIVED_TOPIC) String topic) {
...
}
This won’t work if the object is a String; the topic parameter will also get a reference to object.
If you need metadata about the record in a default method, use this:
@KafkaHandler(isDefault = true)
void listen(Object in, @Header(KafkaHeaders.RECORD_METADATA) ConsumerRecordMetadata meta) {
String topic = meta.topic();
...
}
@KafkaListener Attribute Modification
Starting with version 2.7.2, you can now programmatically modify annotation attributes before the container is created.
To do so, add one or more KafkaListenerAnnotationBeanPostProcessor.AnnotationEnhancer to the application context.
AnnotationEnhancer is a BiFunction<Map<String, Object>, AnnotatedElement, Map<String, Object> and must return a map of attributes.
The attribute values can contain SpEL and/or property placeholders; the enhancer is called before any resolution is performed.
If more than one enhancer is present, and they implement Ordered, they will be invoked in order.
AnnotationEnhancer bean definitions must be declared static because they are required very early in the application context’s lifecycle.
|
An example follows:
@Bean
public static AnnotationEnhancer groupIdEnhancer() {
return (attrs, element) -> {
attrs.put("groupId", attrs.get("id") + "." + (element instanceof Class
? ((Class<?>) element).getSimpleName()
: ((Method) element).getDeclaringClass().getSimpleName()
+ "." + ((Method) element).getName()));
return attrs;
};
}
@KafkaListener Lifecycle Management
The listener containers created for @KafkaListener annotations are not beans in the application context.
Instead, they are registered with an infrastructure bean of type KafkaListenerEndpointRegistry.
This bean is automatically declared by the framework and manages the containers' lifecycles; it will auto-start any containers that have autoStartup set to true.
All containers created by all container factories must be in the same phase.
See Listener Container Auto Startup for more information.
You can manage the lifecycle programmatically by using the registry.
Starting or stopping the registry will start or stop all the registered containers.
Alternatively, you can get a reference to an individual container by using its id attribute.
You can set autoStartup on the annotation, which overrides the default setting configured into the container factory.
You can get a reference to the bean from the application context, such as auto-wiring, to manage its registered containers.
The following examples show how to do so:
@KafkaListener(id = "myContainer", topics = "myTopic", autoStartup = "false")
public void listen(...) { ... }
@Autowired
private KafkaListenerEndpointRegistry registry;
...
this.registry.getListenerContainer("myContainer").start();
...
The registry only maintains the life cycle of containers it manages; containers declared as beans are not managed by the registry and can be obtained from the application context.
A collection of managed containers can be obtained by calling the registry’s getListenerContainers() method.
Version 2.2.5 added a convenience method getAllListenerContainers(), which returns a collection of all containers, including those managed by the registry and those declared as beans.
The collection returned will include any prototype beans that have been initialized, but it will not initialize any lazy bean declarations.
Endpoints registered after the application context has been refreshed will start immediately, regardless of their autoStartup property, to comply with the SmartLifecycle contract, where autoStartup is only considered during application context initialization.
An example of late registration is a bean with a @KafkaListener in prototype scope where an instance is created after the context is initialized.
Starting with version 2.8.7, you can set the registry’s alwaysStartAfterRefresh property to false and then the container’s autoStartup property will define whether or not the container is started.
|
@KafkaListener @Payload Validation
Starting with version 2.2, it is now easier to add a Validator to validate @KafkaListener @Payload arguments.
Previously, you had to configure a custom DefaultMessageHandlerMethodFactory and add it to the registrar.
Now, you can add the validator to the registrar itself.
The following code shows how to do so:
@Configuration
@EnableKafka
public class Config implements KafkaListenerConfigurer {
...
@Override
public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
registrar.setValidator(new MyValidator());
}
}
When you use Spring Boot with the validation starter, a LocalValidatorFactoryBean is auto-configured, as the following example shows:
|
@Configuration
@EnableKafka
public class Config implements KafkaListenerConfigurer {
@Autowired
private LocalValidatorFactoryBean validator;
...
@Override
public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
registrar.setValidator(this.validator);
}
}
The following examples show how to validate:
public static class ValidatedClass {
@Max(10)
private int bar;
public int getBar() {
return this.bar;
}
public void setBar(int bar) {
this.bar = bar;
}
}
@KafkaListener(id="validated", topics = "annotated35", errorHandler = "validationErrorHandler",
containerFactory = "kafkaJsonListenerContainerFactory")
public void validatedListener(@Payload @Valid ValidatedClass val) {
...
}
@Bean
public KafkaListenerErrorHandler validationErrorHandler() {
return (m, e) -> {
...
};
}
Starting with version 2.5.11, validation now works on payloads for @KafkaHandler methods in a class-level listener.
See @KafkaListener on a Class.
Rebalancing Listeners
ContainerProperties has a property called consumerRebalanceListener, which takes an implementation of the Kafka client’s ConsumerRebalanceListener interface.
If this property is not provided, the container configures a logging listener that logs rebalance events at the INFO level.
The framework also adds a sub-interface ConsumerAwareRebalanceListener.
The following listing shows the ConsumerAwareRebalanceListener interface definition:
public interface ConsumerAwareRebalanceListener extends ConsumerRebalanceListener {
void onPartitionsRevokedBeforeCommit(Consumer<?, ?> consumer, Collection<TopicPartition> partitions);
void onPartitionsRevokedAfterCommit(Consumer<?, ?> consumer, Collection<TopicPartition> partitions);
void onPartitionsAssigned(Consumer<?, ?> consumer, Collection<TopicPartition> partitions);
void onPartitionsLost(Consumer<?, ?> consumer, Collection<TopicPartition> partitions);
}
Notice that there are two callbacks when partitions are revoked. The first is called immediately. The second is called after any pending offsets are committed. This is useful if you wish to maintain offsets in some external repository, as the following example shows:
containerProperties.setConsumerRebalanceListener(new ConsumerAwareRebalanceListener() {
@Override
public void onPartitionsRevokedBeforeCommit(Consumer<?, ?> consumer, Collection<TopicPartition> partitions) {
// acknowledge any pending Acknowledgments (if using manual acks)
}
@Override
public void onPartitionsRevokedAfterCommit(Consumer<?, ?> consumer, Collection<TopicPartition> partitions) {
// ...
store(consumer.position(partition));
// ...
}
@Override
public void onPartitionsAssigned(Collection<TopicPartition> partitions) {
// ...
consumer.seek(partition, offsetTracker.getOffset() + 1);
// ...
}
});
Starting with version 2.4, a new method onPartitionsLost() has been added (similar to a method with the same name in ConsumerRebalanceLister).
The default implementation on ConsumerRebalanceLister simply calls onPartionsRevoked.
The default implementation on ConsumerAwareRebalanceListener does nothing.
When supplying the listener container with a custom listener (of either type), it is important that your implementation not call onPartitionsRevoked from onPartitionsLost.
If you implement ConsumerRebalanceListener you should override the default method.
This is because the listener container will call its own onPartitionsRevoked from its implementation of onPartitionsLost after calling the method on your implementation.
If you implementation delegates to the default behavior, onPartitionsRevoked will be called twice each time the Consumer calls that method on the container’s listener.
|
Forwarding Listener Results using @SendTo
Starting with version 2.0, if you also annotate a @KafkaListener with a @SendTo annotation and the method invocation returns a result, the result is forwarded to the topic specified by the @SendTo.
The @SendTo value can have several forms:
-
@SendTo("someTopic")routes to the literal topic -
@SendTo("#{someExpression}")routes to the topic determined by evaluating the expression once during application context initialization. -
@SendTo("!{someExpression}")routes to the topic determined by evaluating the expression at runtime. The#rootobject for the evaluation has three properties:-
request: The inboundConsumerRecord(orConsumerRecordsobject for a batch listener)) -
source: Theorg.springframework.messaging.Message<?>converted from therequest. -
result: The method return result.
-
-
@SendTo(no properties): This is treated as!{source.headers['kafka_replyTopic']}(since version 2.1.3).
Starting with versions 2.1.11 and 2.2.1, property placeholders are resolved within @SendTo values.
The result of the expression evaluation must be a String that represents the topic name.
The following examples show the various ways to use @SendTo:
@KafkaListener(topics = "annotated21")
@SendTo("!{request.value()}") // runtime SpEL
public String replyingListener(String in) {
...
}
@KafkaListener(topics = "${some.property:annotated22}")
@SendTo("#{myBean.replyTopic}") // config time SpEL
public Collection<String> replyingBatchListener(List<String> in) {
...
}
@KafkaListener(topics = "annotated23", errorHandler = "replyErrorHandler")
@SendTo("annotated23reply") // static reply topic definition
public String replyingListenerWithErrorHandler(String in) {
...
}
...
@KafkaListener(topics = "annotated25")
@SendTo("annotated25reply1")
public class MultiListenerSendTo {
@KafkaHandler
public String foo(String in) {
...
}
@KafkaHandler
@SendTo("!{'annotated25reply2'}")
public String bar(@Payload(required = false) KafkaNull nul,
@Header(KafkaHeaders.RECEIVED_KEY) int key) {
...
}
}
In order to support @SendTo, the listener container factory must be provided with a KafkaTemplate (in its replyTemplate property), which is used to send the reply.
This should be a KafkaTemplate and not a ReplyingKafkaTemplate which is used on the client-side for request/reply processing.
When using Spring Boot, boot will auto-configure the template into the factory; when configuring your own factory, it must be set as shown in the examples below.
|
Starting with version 2.2, you can add a ReplyHeadersConfigurer to the listener container factory.
This is consulted to determine which headers you want to set in the reply message.
The following example shows how to add a ReplyHeadersConfigurer:
@Bean
public ConcurrentKafkaListenerContainerFactory<Integer, String> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(cf());
factory.setReplyTemplate(template());
factory.setReplyHeadersConfigurer((k, v) -> k.equals("cat"));
return factory;
}
You can also add more headers if you wish. The following example shows how to do so:
@Bean
public ConcurrentKafkaListenerContainerFactory<Integer, String> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(cf());
factory.setReplyTemplate(template());
factory.setReplyHeadersConfigurer(new ReplyHeadersConfigurer() {
@Override
public boolean shouldCopy(String headerName, Object headerValue) {
return false;
}
@Override
public Map<String, Object> additionalHeaders() {
return Collections.singletonMap("qux", "fiz");
}
});
return factory;
}
When you use @SendTo, you must configure the ConcurrentKafkaListenerContainerFactory with a KafkaTemplate in its replyTemplate property to perform the send.
Spring Boot will automatically wire in its auto configured template (or any if a single instance is present).
Unless you use request/reply semantics only the simple send(topic, value) method is used, so you may wish to create a subclass to generate the partition or key.
The following example shows how to do so:
|
@Bean
public KafkaTemplate<String, String> myReplyingTemplate() {
return new KafkaTemplate<Integer, String>(producerFactory()) {
@Override
public CompletableFuture<SendResult<String, String>> send(String topic, String data) {
return super.send(topic, partitionForData(data), keyForData(data), data);
}
...
};
}
|
If the listener method returns |
When using request/reply semantics, the target partition can be requested by the sender.
|
You can annotate a See Handling Exceptions for more information. |
If a listener method returns an Iterable, by default a record for each element as the value is sent.
Starting with version 2.3.5, set the splitIterables property on @KafkaListener to false and the entire result will be sent as the value of a single ProducerRecord.
This requires a suitable serializer in the reply template’s producer configuration.
However, if the reply is Iterable<Message<?>> the property is ignored and each message is sent separately.
|
Filtering Messages
In certain scenarios, such as rebalancing, a message that has already been processed may be redelivered. The framework cannot know whether such a message has been processed or not. That is an application-level function. This is known as the Idempotent Receiver pattern and Spring Integration provides an implementation of it.
The Spring for Apache Kafka project also provides some assistance by means of the FilteringMessageListenerAdapter class, which can wrap your MessageListener.
This class takes an implementation of RecordFilterStrategy in which you implement the filter method to signal that a message is a duplicate and should be discarded.
This has an additional property called ackDiscarded, which indicates whether the adapter should acknowledge the discarded record.
It is false by default.
When you use @KafkaListener, set the RecordFilterStrategy (and optionally ackDiscarded) on the container factory so that the listener is wrapped in the appropriate filtering adapter.
In addition, a FilteringBatchMessageListenerAdapter is provided, for when you use a batch message listener.
The FilteringBatchMessageListenerAdapter is ignored if your @KafkaListener receives a ConsumerRecords<?, ?> instead of List<ConsumerRecord<?, ?>>, because ConsumerRecords is immutable.
|
Starting with version 2.8.4, you can override the listener container factory’s default RecordFilterStrategy by using the filter property on the listener annotations.
@KafkaListener(id = "filtered", topics = "topic", filter = "differentFilter")
public void listen(Thing thing) {
...
}
Retrying Deliveries
See the DefaultErrorHandler in Handling Exceptions.
Starting @KafkaListener s in Sequence
A common use case is to start a listener after another listener has consumed all the records in a topic.
For example, you may want to load the contents of one or more compacted topics into memory before processing records from other topics.
Starting with version 2.7.3, a new component ContainerGroupSequencer has been introduced.
It uses the @KafkaListener containerGroup property to group containers together and start the containers in the next group, when all the containers in the current group have gone idle.
It is best illustrated with an example.
@KafkaListener(id = "listen1", topics = "topic1", containerGroup = "g1", concurrency = "2")
public void listen1(String in) {
}
@KafkaListener(id = "listen2", topics = "topic2", containerGroup = "g1", concurrency = "2")
public void listen2(String in) {
}
@KafkaListener(id = "listen3", topics = "topic3", containerGroup = "g2", concurrency = "2")
public void listen3(String in) {
}
@KafkaListener(id = "listen4", topics = "topic4", containerGroup = "g2", concurrency = "2")
public void listen4(String in) {
}
@Bean
ContainerGroupSequencer sequencer(KafkaListenerEndpointRegistry registry) {
return new ContainerGroupSequencer(registry, 5000, "g1", "g2");
}
Here, we have 4 listeners in two groups, g1 and g2.
During application context initialization, the sequencer, sets the autoStartup property of all the containers in the provided groups to false.
It also sets the idleEventInterval for any containers (that do not already have one set) to the supplied value (5000ms in this case).
Then, when the sequencer is started by the application context, the containers in the first group are started.
As ListenerContainerIdleEvent s are received, each individual child container in each container is stopped.
When all child containers in a ConcurrentMessageListenerContainer are stopped, the parent container is stopped.
When all containers in a group have been stopped, the containers in the next group are started.
There is no limit to the number of groups or containers in a group.
By default, the containers in the final group (g2 above) are not stopped when they go idle.
To modify that behavior, set stopLastGroupWhenIdle to true on the sequencer.
As an aside; previously, containers in each group were added to a bean of type Collection<MessageListenerContainer> with the bean name being the containerGroup.
These collections are now deprecated in favor of beans of type ContainerGroup with a bean name that is the group name, suffixed with .group; in the example above, there would be 2 beans g1.group and g2.group.
The Collection beans will be removed in a future release.
Using KafkaTemplate to Receive
This section covers how to use KafkaTemplate to receive messages.
Starting with version 2.8, the template has four receive() methods:
ConsumerRecord<K, V> receive(String topic, int partition, long offset);
ConsumerRecord<K, V> receive(String topic, int partition, long offset, Duration pollTimeout);
ConsumerRecords<K, V> receive(Collection<TopicPartitionOffset> requested);
ConsumerRecords<K, V> receive(Collection<TopicPartitionOffset> requested, Duration pollTimeout);
As you can see, you need to know the partition and offset of the record(s) you need to retrieve; a new Consumer is created (and closed) for each operation.
With the last two methods, each record is retrieved individually and the results assembled into a ConsumerRecords object.
When creating the TopicPartitionOffset s for the request, only positive, absolute offsets are supported.
4.1.5. Listener Container Properties
| Property | Default | Description |
|---|---|---|
1 |
The number of records before committing pending offsets when the |
|
|
A chain of |
|
BATCH |
Controls how often offsets are committed - see Committing Offsets. |
|
5000 |
The time in milliseconds after which pending offsets are committed when the |
|
LATEST_ONLY _NO_TX |
Whether or not to commit the initial position on assignment; by default, the initial offset will only be committed if the |
|
false |
Enable out-of-order commits (see Manually Committing Offsets); the consumer is paused and commits are deferred until gaps are filled. |
|
|
When not null, a |
|
(empty string) |
A prefix for the |
|
false |
Set to |
|
false |
Set to |
|
|
When present and |
|
|
A provider for |
|
DEBUG |
The logging level for logs pertaining to committing offsets. |
|
|
A rebalance listener; see Rebalancing Listeners. |
|
30s |
The time to wait for the consumer to start before logging an error; this might happen if, say, you use a task executor with insufficient threads. |
|
|
A task executor to run the consumer threads.
The default executor creates threads named |
|
|
||
|
Exactly Once Semantics mode; see Exactly Once Semantics. |
|
|
When consuming records produced by a transactional producer, and the consumer is positioned at the end of a partition, the lag can incorrectly be reported as greater than zero, due to the pseudo record used to indicate transaction commit/rollback and, possibly, the presence of rolled-back records.
This does not functionally affect the consumer but some users have expressed concern that the "lag" is non-zero.
Set this property to |
|
|
Overrides the consumer |
|
5.0 |
Multiplier for |
|
0 |
Used to slow down deliveries by sleeping the thread between polls.
The time to process a batch of records plus this value must be less than the |
|
|
When set, enables publication of |
|
|
When set, enables publication of |
|
None |
Used to override any arbitrary consumer properties configured on the consumer factory. |
|
|
Set to true to log at INFO level all container properties. |
|
|
The message listener. |
|
|
Whether or not to maintain Micrometer timers for the consumer threads. |
|
empty |
A map of static tags to be added to micrometer metrics. |
|
|
A function that provides dynamic tags, based on the consumer record. |
|
|
When true prevents the container from starting if the confifgured topic(s) are not present on the broker. |
|
30s |
How often to check the state of the consumer threads for |
|
3.0 |
Multiplied by |
|
|
Set to false to log the complete consumer record (in error, debug logs etc) instead of just |
|
|
When the container is paused, stop processing after the current record instead of after processing all the records from the previous poll; the remaining records are retained in memory and will be passed to the listener when the container is resumed. |
|
5000 |
The timeout passed into |
|
100 |
The timeout passed into |
|
false |
True to restart the container if it is stopped due to authorization/authentication exceptions. |
|
|
A scheduler on which to run the consumer monitor task. |
|
10000 |
The maximum time in ms to block the |
|
|
Stop the listener container if a |
|
|
When the container is stopped, stop processing after the current record instead of after processing all the records from the previous poll. |
|
See desc. |
When using a batch listener, if this is |
|
|
The timeout to use when |
|
|
Whether to use sync or async commits for offsets; see |
|
n/a |
The configured topics, topic pattern or explicitly assigned topics/partitions.
Mutually exclusive; at least one must be provided; enforced by |
|
|
See Transactions. |
| Property | Default | Description |
|---|---|---|
|
An |
|
application context |
The event publisher. |
|
See desc. |
Deprecated - see |
|
|
Set a |
|
bean name |
The bean name of the container; suffixed with |
|
See desc. |
|
|
|
The container properties instance. |
|
See desc. |
Deprecated - see |
|
See desc. |
Deprecated - see |
|
See desc. |
The |
|
|
Determines whether the |
|
See desc. |
The bean name for user-configured containers or the |
|
null |
A value to populate in the |
|
(read only) |
True if a consumer pause has been requested. |
|
|
Set a |
|
30s |
When the |
| Property | Default | Description |
|---|---|---|
(read only) |
The partitions currently assigned to this container (explicitly or not). |
|
(read only) |
The partitions currently assigned to this container (explicitly or not). |
|
|
Used by the concurrent container to give each child container’s consumer a unique |
|
n/a |
True if pause has been requested and the consumer has actually paused. |
| Property | Default | Description |
|---|---|---|
|
Set to false to suppress adding a suffix to the |
|
(read only) |
The aggregate of partitions currently assigned to this container’s child |
|
(read only) |
The partitions currently assigned to this container’s child |
|
1 |
The number of child |
|
n/a |
True if pause has been requested and all child containers' consumer has actually paused. |
|
n/a |
A reference to all child |
4.1.6. Dynamically Creating Containers
There are several techniques that can be used to create listener containers at runtime. This section explores some of those techniques.
MessageListener Implementations
If you implement your own listener directly, you can simply use the container factory to create a raw container for that listener:
public class MyListener implements MessageListener<String, String> {
@Override
public void onMessage(ConsumerRecord<String, String> data) {
// ...
}
}
private ConcurrentMessageListenerContainer<String, String> createContainer(
ConcurrentKafkaListenerContainerFactory<String, String> factory, String topic, String group) {
ConcurrentMessageListenerContainer<String, String> container = factory.createContainer(topic);
container.getContainerProperties().setMessageListener(new MyListener());
container.getContainerProperties().setGroupId(group);
container.setBeanName(group);
container.start();
return container;
}
class MyListener : MessageListener<String?, String?> {
override fun onMessage(data: ConsumerRecord<String?, String?>) {
// ...
}
}
private fun createContainer(
factory: ConcurrentKafkaListenerContainerFactory<String, String>, topic: String, group: String
): ConcurrentMessageListenerContainer<String, String> {
val container = factory.createContainer(topic)
container.containerProperties.messageListener = MyListener()
container.containerProperties.groupId = group
container.beanName = group
container.start()
return container
}
Prototype Beans
Containers for methods annotated with @KafkaListener can be created dynamically by declaring the bean as prototype:
public class MyPojo {
private final String id;
private final String topic;
public MyPojo(String id, String topic) {
this.id = id;
this.topic = topic;
}
public String getId() {
return this.id;
}
public String getTopic() {
return this.topic;
}
@KafkaListener(id = "#{__listener.id}", topics = "#{__listener.topic}")
public void listen(String in) {
System.out.println(in);
}
}
@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
MyPojo pojo(String id, String topic) {
return new MyPojo(id, topic);
}
applicationContext.getBean(MyPojo.class, "one", "topic2");
applicationContext.getBean(MyPojo.class, "two", "topic3");
class MyPojo(id: String?, topic: String?) {
@KafkaListener(id = "#{__listener.id}", topics = ["#{__listener.topics}"])
fun listen(`in`: String?) {
println(`in`)
}
}
@Bean
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
fun pojo(id: String?, topic: String?): MyPojo {
return MyPojo(id, topic)
}
applicationContext.getBean(MyPojo::class.java, "one", arrayOf("topic2"))
applicationContext.getBean(MyPojo::class.java, "two", arrayOf("topic3"))
Listeners must have unique IDs.
Starting with version 2.8.9, the KafkaListenerEndpointRegistry has a new method unregisterListenerContainer(String id) to allow you to re-use an id.
Unregistering a container does not stop() the container, you must do that yourself.
|
4.1.7. Application Events
The following Spring application events are published by listener containers and their consumers:
-
ConsumerStartingEvent- published when a consumer thread is first started, before it starts polling. -
ConsumerStartedEvent- published when a consumer is about to start polling. -
ConsumerFailedToStartEvent- published if noConsumerStartingEventis published within theconsumerStartTimeoutcontainer property. This event might signal that the configured task executor has insufficient threads to support the containers it is used in and their concurrency. An error message is also logged when this condition occurs. -
ListenerContainerIdleEvent: published when no messages have been received inidleInterval(if configured). -
ListenerContainerNoLongerIdleEvent: published when a record is consumed after previously publishing aListenerContainerIdleEvent. -
ListenerContainerPartitionIdleEvent: published when no messages have been received from that partition inidlePartitionEventInterval(if configured). -
ListenerContainerPartitionNoLongerIdleEvent: published when a record is consumed from a partition that has previously published aListenerContainerPartitionIdleEvent. -
NonResponsiveConsumerEvent: published when the consumer appears to be blocked in thepollmethod. -
ConsumerPartitionPausedEvent: published by each consumer when a partition is paused. -
ConsumerPartitionResumedEvent: published by each consumer when a partition is resumed. -
ConsumerPausedEvent: published by each consumer when the container is paused. -
ConsumerResumedEvent: published by each consumer when the container is resumed. -
ConsumerStoppingEvent: published by each consumer just before stopping. -
ConsumerStoppedEvent: published after the consumer is closed. See Thread Safety. -
ConsumerRetryAuthEvent: published when authentication or authorization of a consumer fails and is being retried. -
ConsumerRetryAuthSuccessfulEvent: published when authentication or authorization has been retried successfully. Can only occur when there has been aConsumerRetryAuthEventbefore. -
ContainerStoppedEvent: published when all consumers have stopped.
By default, the application context’s event multicaster invokes event listeners on the calling thread.
If you change the multicaster to use an async executor, you must not invoke any Consumer methods when the event contains a reference to the consumer.
|
The ListenerContainerIdleEvent has the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
id: The listener ID (or container bean name). -
idleTime: The time the container had been idle when the event was published. -
topicPartitions: The topics and partitions that the container was assigned at the time the event was generated. -
consumer: A reference to the KafkaConsumerobject. For example, if the consumer’spause()method was previously called, it canresume()when the event is received. -
paused: Whether the container is currently paused. See Pausing and Resuming Listener Containers for more information.
The ListenerContainerNoLongerIdleEvent has the same properties, except idleTime and paused.
The ListenerContainerPartitionIdleEvent has the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
id: The listener ID (or container bean name). -
idleTime: The time partition consumption had been idle when the event was published. -
topicPartition: The topic and partition that triggered the event. -
consumer: A reference to the KafkaConsumerobject. For example, if the consumer’spause()method was previously called, it canresume()when the event is received. -
paused: Whether that partition consumption is currently paused for that consumer. See Pausing and Resuming Listener Containers for more information.
The ListenerContainerPartitionNoLongerIdleEvent has the same properties, except idleTime and paused.
The NonResponsiveConsumerEvent has the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
id: The listener ID (or container bean name). -
timeSinceLastPoll: The time just before the container last calledpoll(). -
topicPartitions: The topics and partitions that the container was assigned at the time the event was generated. -
consumer: A reference to the KafkaConsumerobject. For example, if the consumer’spause()method was previously called, it canresume()when the event is received. -
paused: Whether the container is currently paused. See Pausing and Resuming Listener Containers for more information.
The ConsumerPausedEvent, ConsumerResumedEvent, and ConsumerStopping events have the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
partitions: TheTopicPartitioninstances involved.
The ConsumerPartitionPausedEvent, ConsumerPartitionResumedEvent events have the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
partition: TheTopicPartitioninstance involved.
The ConsumerRetryAuthEvent event has the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child. -
reason-
AUTHENTICATION- the event was published because of an authentication exception. -
AUTHORIZATION- the event was published because of an authorization exception.
-
The ConsumerStartingEvent, ConsumerStartingEvent, ConsumerFailedToStartEvent, ConsumerStoppedEvent, ConsumerRetryAuthSuccessfulEvent and ContainerStoppedEvent events have the following properties:
-
source: The listener container instance that published the event. -
container: The listener container or the parent listener container, if the source container is a child.
All containers (whether a child or a parent) publish ContainerStoppedEvent.
For a parent container, the source and container properties are identical.
In addition, the ConsumerStoppedEvent has the following additional property:
-
reason-
NORMAL- the consumer stopped normally (container was stopped). -
ERROR- ajava.lang.Errorwas thrown. -
FENCED- the transactional producer was fenced and thestopContainerWhenFencedcontainer property istrue. -
AUTH- anAuthenticationExceptionorAuthorizationExceptionwas thrown and theauthExceptionRetryIntervalis not configured. -
NO_OFFSET- there is no offset for a partition and theauto.offset.resetpolicy isnone.
-
You can use this event to restart the container after such a condition:
if (event.getReason.equals(Reason.FENCED)) {
event.getSource(MessageListenerContainer.class).start();
}
Detecting Idle and Non-Responsive Consumers
While efficient, one problem with asynchronous consumers is detecting when they are idle. You might want to take some action if no messages arrive for some period of time.
You can configure the listener container to publish a ListenerContainerIdleEvent when some time passes with no message delivery.
While the container is idle, an event is published every idleEventInterval milliseconds.
To configure this feature, set the idleEventInterval on the container.
The following example shows how to do so:
@Bean
public KafkaMessageListenerContainer(ConsumerFactory<String, String> consumerFactory) {
ContainerProperties containerProps = new ContainerProperties("topic1", "topic2");
...
containerProps.setIdleEventInterval(60000L);
...
KafkaMessageListenerContainer<String, String> container = new KafKaMessageListenerContainer<>(...);
return container;
}
The following example shows how to set the idleEventInterval for a @KafkaListener:
@Bean
public ConcurrentKafkaListenerContainerFactory kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<String, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
...
factory.getContainerProperties().setIdleEventInterval(60000L);
...
return factory;
}
In each of these cases, an event is published once per minute while the container is idle.
If, for some reason, the consumer poll() method does not exit, no messages are received and idle events cannot be generated (this was a problem with early versions of the kafka-clients when the broker wasn’t reachable).
In this case, the container publishes a NonResponsiveConsumerEvent if a poll does not return within 3x the pollTimeout property.
By default, this check is performed once every 30 seconds in each container.
You can modify this behavior by setting the monitorInterval (default 30 seconds) and noPollThreshold (default 3.0) properties in the ContainerProperties when configuring the listener container.
The noPollThreshold should be greater than 1.0 to avoid getting spurious events due to a race condition.
Receiving such an event lets you stop the containers, thus waking the consumer so that it can stop.
Starting with version 2.6.2, if a container has published a ListenerContainerIdleEvent, it will publish a ListenerContainerNoLongerIdleEvent when a record is subsequently received.
Event Consumption
You can capture these events by implementing ApplicationListener — either a general listener or one narrowed to only receive this specific event.
You can also use @EventListener, introduced in Spring Framework 4.2.
The next example combines @KafkaListener and @EventListener into a single class.
You should understand that the application listener gets events for all containers, so you may need to check the listener ID if you want to take specific action based on which container is idle.
You can also use the @EventListener condition for this purpose.
See Application Events for information about event properties.
The event is normally published on the consumer thread, so it is safe to interact with the Consumer object.
The following example uses both @KafkaListener and @EventListener:
public class Listener {
@KafkaListener(id = "qux", topics = "annotated")
public void listen4(@Payload String foo, Acknowledgment ack) {
...
}
@EventListener(condition = "event.listenerId.startsWith('qux-')")
public void eventHandler(ListenerContainerIdleEvent event) {
...
}
}
Event listeners see events for all containers.
Consequently, in the preceding example, we narrow the events received based on the listener ID.
Since containers created for the @KafkaListener support concurrency, the actual containers are named id-n where the n is a unique value for each instance to support the concurrency.
That is why we use startsWith in the condition.
|
If you wish to use the idle event to stop the lister container, you should not call container.stop() on the thread that calls the listener.
Doing so causes delays and unnecessary log messages.
Instead, you should hand off the event to a different thread that can then stop the container.
Also, you should not stop() the container instance if it is a child container.
You should stop the concurrent container instead.
|
Current Positions when Idle
Note that you can obtain the current positions when idle is detected by implementing ConsumerSeekAware in your listener.
See onIdleContainer() in Seeking to a Specific Offset.
4.1.8. Topic/Partition Initial Offset
There are several ways to set the initial offset for a partition.
When manually assigning partitions, you can set the initial offset (if desired) in the configured TopicPartitionOffset arguments (see Message Listener Containers).
You can also seek to a specific offset at any time.
When you use group management where the broker assigns partitions:
-
For a new
group.id, the initial offset is determined by theauto.offset.resetconsumer property (earliestorlatest). -
For an existing group ID, the initial offset is the current offset for that group ID. You can, however, seek to a specific offset during initialization (or at any time thereafter).
4.1.9. Seeking to a Specific Offset
In order to seek, your listener must implement ConsumerSeekAware, which has the following methods:
void registerSeekCallback(ConsumerSeekCallback callback);
void onPartitionsAssigned(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback);
void onPartitionsRevoked(Collection<TopicPartition> partitions)
void onIdleContainer(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback);
The registerSeekCallback is called when the container is started and whenever partitions are assigned.
You should use this callback when seeking at some arbitrary time after initialization.
You should save a reference to the callback.
If you use the same listener in multiple containers (or in a ConcurrentMessageListenerContainer), you should store the callback in a ThreadLocal or some other structure keyed by the listener Thread.
When using group management, onPartitionsAssigned is called when partitions are assigned.
You can use this method, for example, for setting initial offsets for the partitions, by calling the callback.
You can also use this method to associate this thread’s callback with the assigned partitions (see the example below).
You must use the callback argument, not the one passed into registerSeekCallback.
Starting with version 2.5.5, this method is called, even when using manual partition assignment.
onPartitionsRevoked is called when the container is stopped or Kafka revokes assignments.
You should discard this thread’s callback and remove any associations to the revoked partitions.
The callback has the following methods:
void seek(String topic, int partition, long offset);
void seekToBeginning(String topic, int partition);
void seekToBeginning(Collection=<TopicPartitions> partitions);
void seekToEnd(String topic, int partition);
void seekToEnd(Collection=<TopicPartitions> partitions);
void seekRelative(String topic, int partition, long offset, boolean toCurrent);
void seekToTimestamp(String topic, int partition, long timestamp);
void seekToTimestamp(Collection<TopicPartition> topicPartitions, long timestamp);
seekRelative was added in version 2.3, to perform relative seeks.
-
offsetnegative andtoCurrentfalse- seek relative to the end of the partition. -
offsetpositive andtoCurrentfalse- seek relative to the beginning of the partition. -
offsetnegative andtoCurrenttrue- seek relative to the current position (rewind). -
offsetpositive andtoCurrenttrue- seek relative to the current position (fast forward).
The seekToTimestamp methods were also added in version 2.3.
When seeking to the same timestamp for multiple partitions in the onIdleContainer or onPartitionsAssigned methods, the second method is preferred because it is more efficient to find the offsets for the timestamps in a single call to the consumer’s offsetsForTimes method.
When called from other locations, the container will gather all timestamp seek requests and make one call to offsetsForTimes.
|
You can also perform seek operations from onIdleContainer() when an idle container is detected.
See Detecting Idle and Non-Responsive Consumers for how to enable idle container detection.
The seekToBeginning method that accepts a collection is useful, for example, when processing a compacted topic and you wish to seek to the beginning every time the application is started:
|
public class MyListener implements ConsumerSeekAware {
...
@Override
public void onPartitionsAssigned(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback) {
callback.seekToBeginning(assignments.keySet());
}
}
To arbitrarily seek at runtime, use the callback reference from the registerSeekCallback for the appropriate thread.
Here is a trivial Spring Boot application that demonstrates how to use the callback; it sends 10 records to the topic; hitting <Enter> in the console causes all partitions to seek to the beginning.
@SpringBootApplication
public class SeekExampleApplication {
public static void main(String[] args) {
SpringApplication.run(SeekExampleApplication.class, args);
}
@Bean
public ApplicationRunner runner(Listener listener, KafkaTemplate<String, String> template) {
return args -> {
IntStream.range(0, 10).forEach(i -> template.send(
new ProducerRecord<>("seekExample", i % 3, "foo", "bar")));
while (true) {
System.in.read();
listener.seekToStart();
}
};
}
@Bean
public NewTopic topic() {
return new NewTopic("seekExample", 3, (short) 1);
}
}
@Component
class Listener implements ConsumerSeekAware {
private static final Logger logger = LoggerFactory.getLogger(Listener.class);
private final ThreadLocal<ConsumerSeekCallback> callbackForThread = new ThreadLocal<>();
private final Map<TopicPartition, ConsumerSeekCallback> callbacks = new ConcurrentHashMap<>();
@Override
public void registerSeekCallback(ConsumerSeekCallback callback) {
this.callbackForThread.set(callback);
}
@Override
public void onPartitionsAssigned(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback) {
assignments.keySet().forEach(tp -> this.callbacks.put(tp, this.callbackForThread.get()));
}
@Override
public void onPartitionsRevoked(Collection<TopicPartition> partitions) {
partitions.forEach(tp -> this.callbacks.remove(tp));
this.callbackForThread.remove();
}
@Override
public void onIdleContainer(Map<TopicPartition, Long> assignments, ConsumerSeekCallback callback) {
}
@KafkaListener(id = "seekExample", topics = "seekExample", concurrency = "3")
public void listen(ConsumerRecord<String, String> in) {
logger.info(in.toString());
}
public void seekToStart() {
this.callbacks.forEach((tp, callback) -> callback.seekToBeginning(tp.topic(), tp.partition()));
}
}
To make things simpler, version 2.3 added the AbstractConsumerSeekAware class, which keeps track of which callback is to be used for a topic/partition.
The following example shows how to seek to the last record processed, in each partition, each time the container goes idle.
It also has methods that allow arbitrary external calls to rewind partitions by one record.
public class SeekToLastOnIdleListener extends AbstractConsumerSeekAware {
@KafkaListener(id = "seekOnIdle", topics = "seekOnIdle")
public void listen(String in) {
...
}
@Override
public void onIdleContainer(Map<org.apache.kafka.common.TopicPartition, Long> assignments,
ConsumerSeekCallback callback) {
assignments.keySet().forEach(tp -> callback.seekRelative(tp.topic(), tp.partition(), -1, true));
}
/**
* Rewind all partitions one record.
*/
public void rewindAllOneRecord() {
getSeekCallbacks()
.forEach((tp, callback) ->
callback.seekRelative(tp.topic(), tp.partition(), -1, true));
}
/**
* Rewind one partition one record.
*/
public void rewindOnePartitionOneRecord(String topic, int partition) {
getSeekCallbackFor(new org.apache.kafka.common.TopicPartition(topic, partition))
.seekRelative(topic, partition, -1, true);
}
}
Version 2.6 added convenience methods to the abstract class:
-
seekToBeginning()- seeks all assigned partitions to the beginning -
seekToEnd()- seeks all assigned partitions to the end -
seekToTimestamp(long time)- seeks all assigned partitions to the offset represented by that timestamp.
Example:
public class MyListener extends AbstractConsumerSeekAware {
@KafkaListener(...)
void listn(...) {
...
}
}
public class SomeOtherBean {
MyListener listener;
...
void someMethod() {
this.listener.seekToTimestamp(System.currentTimeMillis - 60_000);
}
}
4.1.10. Container factory
As discussed in @KafkaListener Annotation, a ConcurrentKafkaListenerContainerFactory is used to create containers for annotated methods.
Starting with version 2.2, you can use the same factory to create any ConcurrentMessageListenerContainer.
This might be useful if you want to create several containers with similar properties or you wish to use some externally configured factory, such as the one provided by Spring Boot auto-configuration.
Once the container is created, you can further modify its properties, many of which are set by using container.getContainerProperties().
The following example configures a ConcurrentMessageListenerContainer:
@Bean
public ConcurrentMessageListenerContainer<String, String>(
ConcurrentKafkaListenerContainerFactory<String, String> factory) {
ConcurrentMessageListenerContainer<String, String> container =
factory.createContainer("topic1", "topic2");
container.setMessageListener(m -> { ... } );
return container;
}
Containers created this way are not added to the endpoint registry.
They should be created as @Bean definitions so that they are registered with the application context.
|
Starting with version 2.3.4, you can add a ContainerCustomizer to the factory to further configure each container after it has been created and configured.
@Bean
public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
...
factory.setContainerCustomizer(container -> { /* customize the container */ });
return factory;
}
4.1.11. Thread Safety
When using a concurrent message listener container, a single listener instance is invoked on all consumer threads. Listeners, therefore, need to be thread-safe, and it is preferable to use stateless listeners. If it is not possible to make your listener thread-safe or adding synchronization would significantly reduce the benefit of adding concurrency, you can use one of a few techniques:
-
Use
ncontainers withconcurrency=1with a prototype scopedMessageListenerbean so that each container gets its own instance (this is not possible when using@KafkaListener). -
Keep the state in
ThreadLocal<?>instances. -
Have the singleton listener delegate to a bean that is declared in
SimpleThreadScope(or a similar scope).
To facilitate cleaning up thread state (for the second and third items in the preceding list), starting with version 2.2, the listener container publishes a ConsumerStoppedEvent when each thread exits.
You can consume these events with an ApplicationListener or @EventListener method to remove ThreadLocal<?> instances or remove() thread-scoped beans from the scope.
Note that SimpleThreadScope does not destroy beans that have a destruction interface (such as DisposableBean), so you should destroy() the instance yourself.
| By default, the application context’s event multicaster invokes event listeners on the calling thread. If you change the multicaster to use an async executor, thread cleanup is not effective. |
4.1.12. Monitoring
Monitoring Listener Performance
Starting with version 2.3, the listener container will automatically create and update Micrometer Timer s for the listener, if Micrometer is detected on the class path, and a single MeterRegistry is present in the application context.
The timers can be disabled by setting the ContainerProperty micrometerEnabled to false.
Two timers are maintained - one for successful calls to the listener and one for failures.
The timers are named spring.kafka.listener and have the following tags:
-
name: (container bean name) -
result:successorfailure -
exception:noneorListenerExecutionFailedException
You can add additional tags using the ContainerProperties micrometerTags property.
Starting with versions 2.9.8, 3.0.6, you can provide a function in ContainerProperties micrometerTagsProvider; the function receives the ConsumerRecord<?, ?> and returns tags which can be based on that record, and merged with any static tags in micrometerTags.
With the concurrent container, timers are created for each thread and the name tag is suffixed with -n where n is 0 to concurrency-1.
|
Monitoring KafkaTemplate Performance
Starting with version 2.5, the template will automatically create and update Micrometer Timer s for send operations, if Micrometer is detected on the class path, and a single MeterRegistry is present in the application context.
The timers can be disabled by setting the template’s micrometerEnabled property to false.
Two timers are maintained - one for successful calls to the listener and one for failures.
The timers are named spring.kafka.template and have the following tags:
-
name: (template bean name) -
result:successorfailure -
exception:noneor the exception class name for failures
You can add additional tags using the template’s micrometerTags property.
Starting with versions 2.9.8, 3.0.6, you can provide a KafkaTemplate.setMicrometerTagsProvider(Function<ProducerRecord<?, ?>, Map<String, String>>) property; the function receives the ProducerRecord<?, ?> and returns tags which can be based on that record, and merged with any static tags in micrometerTags.
Micrometer Native Metrics
Starting with version 2.5, the framework provides Factory Listeners to manage a Micrometer KafkaClientMetrics instance whenever producers and consumers are created and closed.
To enable this feature, simply add the listeners to your producer and consumer factories:
@Bean
public ConsumerFactory<String, String> myConsumerFactory() {
Map<String, Object> configs = consumerConfigs();
...
DefaultKafkaConsumerFactory<String, String> cf = new DefaultKafkaConsumerFactory<>(configs);
...
cf.addListener(new MicrometerConsumerListener<String, String>(meterRegistry(),
Collections.singletonList(new ImmutableTag("customTag", "customTagValue"))));
...
return cf;
}
@Bean
public ProducerFactory<String, String> myProducerFactory() {
Map<String, Object> configs = producerConfigs();
configs.put(ProducerConfig.CLIENT_ID_CONFIG, "myClientId");
...
DefaultKafkaProducerFactory<String, String> pf = new DefaultKafkaProducerFactory<>(configs);
...
pf.addListener(new MicrometerProducerListener<String, String>(meterRegistry(),
Collections.singletonList(new ImmutableTag("customTag", "customTagValue"))));
...
return pf;
}
The consumer/producer id passed to the listener is added to the meter’s tags with tag name spring.id.
double count = this.meterRegistry.get("kafka.producer.node.incoming.byte.total")
.tag("customTag", "customTagValue")
.tag("spring.id", "myProducerFactory.myClientId-1")
.functionCounter()
.count()
A similar listener is provided for the StreamsBuilderFactoryBean - see KafkaStreams Micrometer Support.
Micrometer Observation
Using Micrometer for observation is now supported, since version 3.0, for the KafkaTemplate and listener containers.
Set observationEnabled to true on the KafkaTemplate and ContainerProperties to enable observation; this will disable Micrometer Timers because the timers will now be managed with each observation.
Refer to Micrometer Tracing for more information.
To add tags to timers/traces, configure a custom KafkaTemplateObservationConvention or KafkaListenerObservationConvention to the template or listener container, respectively.
The default implementations add the bean.name tag for template observations and listener.id tag for containers.
You can either subclass DefaultKafkaTemplateObservationConvention or DefaultKafkaListenerObservationConvention or provide completely new implementations.
See Micrometer Observation Documentation for details of the default observations that are recorded.
Starting with version 3.0.6, you can add dynamic tags to the timers and traces, based on information in the consumer or producer records.
To do so, add a custom KafkaListenerObservationConvention and/or KafkaTemplateObservationConvention to the listener container properties or KafkaTemplate respectively.
The record property in both observation contexts contains the ConsumerRecord or ProducerRecord respectively.
4.1.13. Transactions
This section describes how Spring for Apache Kafka supports transactions.
Overview
The 0.11.0.0 client library added support for transactions. Spring for Apache Kafka adds support in the following ways:
-
KafkaTransactionManager: Used with normal Spring transaction support (@Transactional,TransactionTemplateetc). -
Transactional
KafkaMessageListenerContainer -
Local transactions with
KafkaTemplate -
Transaction synchronization with other transaction managers
Transactions are enabled by providing the DefaultKafkaProducerFactory with a transactionIdPrefix.
In that case, instead of managing a single shared Producer, the factory maintains a cache of transactional producers.
When the user calls close() on a producer, it is returned to the cache for reuse instead of actually being closed.
The transactional.id property of each producer is transactionIdPrefix + n, where n starts with 0 and is incremented for each new producer.
In previous versions of Spring for Apache Kafka, the transactional.id was generated differently for transactions started by a listener container with a record-based listener, to support fencing zombies, which is not necessary any more, with EOSMode.V2 being the only option starting with 3.0.
For applications running with multiple instances, the transactionIdPrefix must be unique per instance.
Also see Exactly Once Semantics.
Also see transactionIdPrefix.
With Spring Boot, it is only necessary to set the spring.kafka.producer.transaction-id-prefix property - Boot will automatically configure a KafkaTransactionManager bean and wire it into the listener container.
Starting with version 2.5.8, you can now configure the maxAge property on the producer factory.
This is useful when using transactional producers that might lay idle for the broker’s transactional.id.expiration.ms.
With current kafka-clients, this can cause a ProducerFencedException without a rebalance.
By setting the maxAge to less than transactional.id.expiration.ms, the factory will refresh the producer if it is past it’s max age.
|
Using KafkaTransactionManager
The KafkaTransactionManager is an implementation of Spring Framework’s PlatformTransactionManager.
It is provided with a reference to the producer factory in its constructor.
If you provide a custom producer factory, it must support transactions.
See ProducerFactory.transactionCapable().
You can use the KafkaTransactionManager with normal Spring transaction support (@Transactional, TransactionTemplate, and others).
If a transaction is active, any KafkaTemplate operations performed within the scope of the transaction use the transaction’s Producer.
The manager commits or rolls back the transaction, depending on success or failure.
You must configure the KafkaTemplate to use the same ProducerFactory as the transaction manager.
Transaction Synchronization
This section refers to producer-only transactions (transactions not started by a listener container); see Using Consumer-Initiated Transactions for information about chaining transactions when the container starts the transaction.
If you want to send records to kafka and perform some database updates, you can use normal Spring transaction management with, say, a DataSourceTransactionManager.
@Transactional
public void process(List<Thing> things) {
things.forEach(thing -> this.kafkaTemplate.send("topic", thing));
updateDb(things);
}
The interceptor for the @Transactional annotation starts the transaction and the KafkaTemplate will synchronize a transaction with that transaction manager; each send will participate in that transaction.
When the method exits, the database transaction will commit followed by the Kafka transaction.
If you wish the commits to be performed in the reverse order (Kafka first), use nested @Transactional methods, with the outer method configured to use the DataSourceTransactionManager, and the inner method configured to use the KafkaTransactionManager.
See Examples of Kafka Transactions with Other Transaction Managers for examples of an application that synchronizes JDBC and Kafka transactions in Kafka-first or DB-first configurations.
| Starting with versions 2.5.17, 2.6.12, 2.7.9 and 2.8.0, if the commit fails on the synchronized transaction (after the primary transaction has committed), the exception will be thrown to the caller. Previously, this was silently ignored (logged at debug). Applications should take remedial action, if necessary, to compensate for the committed primary transaction. |
Using Consumer-Initiated Transactions
The ChainedKafkaTransactionManager is now deprecated, since version 2.7; see the javadocs for its super class ChainedTransactionManager for more information.
Instead, use a KafkaTransactionManager in the container to start the Kafka transaction and annotate the listener method with @Transactional to start the other transaction.
See Examples of Kafka Transactions with Other Transaction Managers for an example application that chains JDBC and Kafka transactions.
KafkaTemplate Local Transactions
You can use the KafkaTemplate to execute a series of operations within a local transaction.
The following example shows how to do so:
boolean result = template.executeInTransaction(t -> {
t.sendDefault("thing1", "thing2");
t.sendDefault("cat", "hat");
return true;
});
The argument in the callback is the template itself (this).
If the callback exits normally, the transaction is committed.
If an exception is thrown, the transaction is rolled back.
If there is a KafkaTransactionManager (or synchronized) transaction in process, it is not used.
Instead, a new "nested" transaction is used.
|
transactionIdPrefix
With EOSMode.V2 (aka BETA), the only supported mode, it is no longer necessary to use the same transactional.id, even for consumer-initiated transactions; in fact, it must be unique on each instance the same as for producer-initiated transactions.
This property must have a different value on each application instance.
KafkaTemplate Transactional and non-Transactional Publishing
Normally, when a KafkaTemplate is transactional (configured with a transaction-capable producer factory), transactions are required.
The transaction can be started by a TransactionTemplate, a @Transactional method, calling executeInTransaction, or by a listener container, when configured with a KafkaTransactionManager.
Any attempt to use the template outside the scope of a transaction results in the template throwing an IllegalStateException.
Starting with version 2.4.3, you can set the template’s allowNonTransactional property to true.
In that case, the template will allow the operation to run without a transaction, by calling the ProducerFactory 's createNonTransactionalProducer() method; the producer will be cached, or thread-bound, as normal for reuse.
See Using DefaultKafkaProducerFactory.
Transactions with Batch Listeners
When a listener fails while transactions are being used, the AfterRollbackProcessor is invoked to take some action after the rollback occurs.
When using the default AfterRollbackProcessor with a record listener, seeks are performed so that the failed record will be redelivered.
With a batch listener, however, the whole batch will be redelivered because the framework doesn’t know which record in the batch failed.
See After-rollback Processor for more information.
When using a batch listener, version 2.4.2 introduced an alternative mechanism to deal with failures while processing a batch; the BatchToRecordAdapter.
When a container factory with batchListener set to true is configured with a BatchToRecordAdapter, the listener is invoked with one record at a time.
This enables error handling within the batch, while still making it possible to stop processing the entire batch, depending on the exception type.
A default BatchToRecordAdapter is provided, that can be configured with a standard ConsumerRecordRecoverer such as the DeadLetterPublishingRecoverer.
The following test case configuration snippet illustrates how to use this feature:
public static class TestListener {
final List<String> values = new ArrayList<>();
@KafkaListener(id = "batchRecordAdapter", topics = "test")
public void listen(String data) {
values.add(data);
if ("bar".equals(data)) {
throw new RuntimeException("reject partial");
}
}
}
@Configuration
@EnableKafka
public static class Config {
ConsumerRecord<?, ?> failed;
@Bean
public TestListener test() {
return new TestListener();
}
@Bean
public ConsumerFactory<?, ?> consumerFactory() {
return mock(ConsumerFactory.class);
}
@Bean
public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory factory = new ConcurrentKafkaListenerContainerFactory();
factory.setConsumerFactory(consumerFactory());
factory.setBatchListener(true);
factory.setBatchToRecordAdapter(new DefaultBatchToRecordAdapter<>((record, ex) -> {
this.failed = record;
}));
return factory;
}
}
4.1.14. Exactly Once Semantics
You can provide a listener container with a KafkaAwareTransactionManager instance.
When so configured, the container starts a transaction before invoking the listener.
Any KafkaTemplate operations performed by the listener participate in the transaction.
If the listener successfully processes the record (or multiple records, when using a BatchMessageListener), the container sends the offset(s) to the transaction by using producer.sendOffsetsToTransaction()), before the transaction manager commits the transaction.
If the listener throws an exception, the transaction is rolled back and the consumer is repositioned so that the rolled-back record(s) can be retrieved on the next poll.
See After-rollback Processor for more information and for handling records that repeatedly fail.
Using transactions enables Exactly Once Semantics (EOS).
This means that, for a read→process-write sequence, it is guaranteed that the sequence is completed exactly once.
(The read and process are have at least once semantics).
Spring for Apache Kafka version 3.0 and later only supports EOSMode.V2:
-
V2- aka fetch-offset-request fencing (since version 2.5)
| This requires the brokers to be version 2.5 or later. |
With mode V2, it is not necessary to have a producer for each group.id/topic/partition because consumer metadata is sent along with the offsets to the transaction and the broker can determine if the producer is fenced using that information instead.
Refer to KIP-447 for more information.
V2 was previously BETA; the EOSMode has been changed to align the framework with KIP-732.
4.1.15. Wiring Spring Beans into Producer/Consumer Interceptors
Apache Kafka provides a mechanism to add interceptors to producers and consumers.
These objects are managed by Kafka, not Spring, and so normal Spring dependency injection won’t work for wiring in dependent Spring Beans.
However, you can manually wire in those dependencies using the interceptor config() method.
The following Spring Boot application shows how to do this by overriding boot’s default factories to add some dependent bean into the configuration properties.
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Bean
public ConsumerFactory<?, ?> kafkaConsumerFactory(SomeBean someBean) {
Map<String, Object> consumerProperties = new HashMap<>();
// consumerProperties.put(..., ...)
// ...
consumerProperties.put(ConsumerConfig.INTERCEPTOR_CLASSES_CONFIG, MyConsumerInterceptor.class.getName());
consumerProperties.put("some.bean", someBean);
return new DefaultKafkaConsumerFactory<>(consumerProperties);
}
@Bean
public ProducerFactory<?, ?> kafkaProducerFactory(SomeBean someBean) {
Map<String, Object> producerProperties = new HashMap<>();
// producerProperties.put(..., ...)
// ...
Map<String, Object> producerProperties = properties.buildProducerProperties();
producerProperties.put(ProducerConfig.INTERCEPTOR_CLASSES_CONFIG, MyProducerInterceptor.class.getName());
producerProperties.put("some.bean", someBean);
DefaultKafkaProducerFactory<?, ?> factory = new DefaultKafkaProducerFactory<>(producerProperties);
return factory;
}
@Bean
public SomeBean someBean() {
return new SomeBean();
}
@KafkaListener(id = "kgk897", topics = "kgh897")
public void listen(String in) {
System.out.println("Received " + in);
}
@Bean
public ApplicationRunner runner(KafkaTemplate<String, String> template) {
return args -> template.send("kgh897", "test");
}
@Bean
public NewTopic kRequests() {
return TopicBuilder.name("kgh897")
.partitions(1)
.replicas(1)
.build();
}
}
public class SomeBean {
public void someMethod(String what) {
System.out.println(what + " in my foo bean");
}
}
public class MyProducerInterceptor implements ProducerInterceptor<String, String> {
private SomeBean bean;
@Override
public void configure(Map<String, ?> configs) {
this.bean = (SomeBean) configs.get("some.bean");
}
@Override
public ProducerRecord<String, String> onSend(ProducerRecord<String, String> record) {
this.bean.someMethod("producer interceptor");
return record;
}
@Override
public void onAcknowledgement(RecordMetadata metadata, Exception exception) {
}
@Override
public void close() {
}
}
public class MyConsumerInterceptor implements ConsumerInterceptor<String, String> {
private SomeBean bean;
@Override
public void configure(Map<String, ?> configs) {
this.bean = (SomeBean) configs.get("some.bean");
}
@Override
public ConsumerRecords<String, String> onConsume(ConsumerRecords<String, String> records) {
this.bean.someMethod("consumer interceptor");
return records;
}
@Override
public void onCommit(Map<TopicPartition, OffsetAndMetadata> offsets) {
}
@Override
public void close() {
}
}
Result:
producer interceptor in my foo bean
consumer interceptor in my foo bean
Received test4.1.16. Producer Interceptor Managed in Spring
Starting with version 3.0.0, when it comes to a producer interceptor, you can let Spring manage it directly as a bean instead of providing the class name of the interceptor to the Apache Kafka producer configuration.
If you go with this approach, then you need to set this producer interceptor on KafkaTemplate.
Following is an example using the same MyProducerInterceptor from above, but changed to not use the internal config property.
public class MyProducerInterceptor implements ProducerInterceptor<String, String> {
private final SomeBean bean;
public MyProducerInterceptor(SomeBean bean) {
this.bean = bean;
}
@Override
public void configure(Map<String, ?> configs) {
}
@Override
public ProducerRecord<String, String> onSend(ProducerRecord<String, String> record) {
this.bean.someMethod("producer interceptor");
return record;
}
@Override
public void onAcknowledgement(RecordMetadata metadata, Exception exception) {
}
@Override
public void close() {
}
}
@Bean
public MyProducerInterceptor myProducerInterceptor(SomeBean someBean) {
return new MyProducerInterceptor(someBean);
}
@Bean
public KafkaTemplate<String, String> kafkaTemplate(ProducerFactory<String, String> pf, MyProducerInterceptor myProducerInterceptor) {
KafkaTemplate<String, String> kafkaTemplate = new KafkaTemplate<String, String>(pf);
kafkaTemplate.setProducerInterceptor(myProducerInterceptor);
}Right before the records are sent, the onSend method of the producer interceptor is invoked.
Once the server sends an acknowledgement on publishing the data, then the onAcknowledgement method is invoked.
The onAcknowledgement is called right before the producer invokes any user callbacks.
If you have multiple such producer interceptors managed through Spring that need to be applied on the KafkaTemplate, you need to use CompositeProducerInterceptor instead.
CompositeProducerInterceptor allows individual producer interceptors to be added in order.
The methods from the underlying ProducerInterceptor implementations are invoked in the order as they were added to the CompositeProducerInterceptor.
4.1.17. Pausing and Resuming Listener Containers
Version 2.1.3 added pause() and resume() methods to listener containers.
Previously, you could pause a consumer within a ConsumerAwareMessageListener and resume it by listening for a ListenerContainerIdleEvent, which provides access to the Consumer object.
While you could pause a consumer in an idle container by using an event listener, in some cases, this was not thread-safe, since there is no guarantee that the event listener is invoked on the consumer thread.
To safely pause and resume consumers, you should use the pause and resume methods on the listener containers.
A pause() takes effect just before the next poll(); a resume() takes effect just after the current poll() returns.
When a container is paused, it continues to poll() the consumer, avoiding a rebalance if group management is being used, but it does not retrieve any records.
See the Kafka documentation for more information.
Starting with version 2.1.5, you can call isPauseRequested() to see if pause() has been called.
However, the consumers might not have actually paused yet.
isConsumerPaused() returns true if all Consumer instances have actually paused.
In addition (also since 2.1.5), ConsumerPausedEvent and ConsumerResumedEvent instances are published with the container as the source property and the TopicPartition instances involved in the partitions property.
Starting with version 2.9, a new container property pauseImmediate, when set to true, causes the pause to take effect after the current record is processed.
By default, the pause takes effect when all of the records from the previous poll have been processed.
See [pauseImmediate].
The following simple Spring Boot application demonstrates by using the container registry to get a reference to a @KafkaListener method’s container and pausing or resuming its consumers as well as receiving the corresponding events:
@SpringBootApplication
public class Application implements ApplicationListener<KafkaEvent> {
public static void main(String[] args) {
SpringApplication.run(Application.class, args).close();
}
@Override
public void onApplicationEvent(KafkaEvent event) {
System.out.println(event);
}
@Bean
public ApplicationRunner runner(KafkaListenerEndpointRegistry registry,
KafkaTemplate<String, String> template) {
return args -> {
template.send("pause.resume.topic", "thing1");
Thread.sleep(10_000);
System.out.println("pausing");
registry.getListenerContainer("pause.resume").pause();
Thread.sleep(10_000);
template.send("pause.resume.topic", "thing2");
Thread.sleep(10_000);
System.out.println("resuming");
registry.getListenerContainer("pause.resume").resume();
Thread.sleep(10_000);
};
}
@KafkaListener(id = "pause.resume", topics = "pause.resume.topic")
public void listen(String in) {
System.out.println(in);
}
@Bean
public NewTopic topic() {
return TopicBuilder.name("pause.resume.topic")
.partitions(2)
.replicas(1)
.build();
}
}
The following listing shows the results of the preceding example:
partitions assigned: [pause.resume.topic-1, pause.resume.topic-0]
thing1
pausing
ConsumerPausedEvent [partitions=[pause.resume.topic-1, pause.resume.topic-0]]
resuming
ConsumerResumedEvent [partitions=[pause.resume.topic-1, pause.resume.topic-0]]
thing24.1.18. Pausing and Resuming Partitions on Listener Containers
Since version 2.7 you can pause and resume the consumption of specific partitions assigned to that consumer by using the pausePartition(TopicPartition topicPartition) and resumePartition(TopicPartition topicPartition) methods in the listener containers.
The pausing and resuming takes place respectively before and after the poll() similar to the pause() and resume() methods.
The isPartitionPauseRequested() method returns true if pause for that partition has been requested.
The isPartitionPaused() method returns true if that partition has effectively been paused.
Also since version 2.7 ConsumerPartitionPausedEvent and ConsumerPartitionResumedEvent instances are published with the container as the source property and the TopicPartition instance.
4.1.19. Serialization, Deserialization, and Message Conversion
Overview
Apache Kafka provides a high-level API for serializing and deserializing record values as well as their keys.
It is present with the org.apache.kafka.common.serialization.Serializer<T> and
org.apache.kafka.common.serialization.Deserializer<T> abstractions with some built-in implementations.
Meanwhile, we can specify serializer and deserializer classes by using Producer or Consumer configuration properties.
The following example shows how to do so:
props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, IntegerDeserializer.class);
props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class);
...
props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, IntegerSerializer.class);
props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, StringSerializer.class);
For more complex or particular cases, the KafkaConsumer (and, therefore, KafkaProducer) provides overloaded
constructors to accept Serializer and Deserializer instances for keys and values, respectively.
When you use this API, the DefaultKafkaProducerFactory and DefaultKafkaConsumerFactory also provide properties (through constructors or setter methods) to inject custom Serializer and Deserializer instances into the target Producer or Consumer.
Also, you can pass in Supplier<Serializer> or Supplier<Deserializer> instances through constructors - these Supplier s are called on creation of each Producer or Consumer.
String serialization
Since version 2.5, Spring for Apache Kafka provides ToStringSerializer and ParseStringDeserializer classes that use String representation of entities.
They rely on methods toString and some Function<String> or BiFunction<String, Headers> to parse the String and populate properties of an instance.
Usually, this would invoke some static method on the class, such as parse:
ToStringSerializer<Thing> thingSerializer = new ToStringSerializer<>();
//...
ParseStringDeserializer<Thing> deserializer = new ParseStringDeserializer<>(Thing::parse);
By default, the ToStringSerializer is configured to convey type information about the serialized entity in the record Headers.
You can disable this by setting the addTypeInfo property to false.
This information can be used by ParseStringDeserializer on the receiving side.
-
ToStringSerializer.ADD_TYPE_INFO_HEADERS(defaulttrue): You can set it tofalseto disable this feature on theToStringSerializer(sets theaddTypeInfoproperty).
ParseStringDeserializer<Object> deserializer = new ParseStringDeserializer<>((str, headers) -> {
byte[] header = headers.lastHeader(ToStringSerializer.VALUE_TYPE).value();
String entityType = new String(header);
if (entityType.contains("Thing")) {
return Thing.parse(str);
}
else {
// ...parsing logic
}
});
You can configure the Charset used to convert String to/from byte[] with the default being UTF-8.
You can configure the deserializer with the name of the parser method using ConsumerConfig properties:
-
ParseStringDeserializer.KEY_PARSER -
ParseStringDeserializer.VALUE_PARSER
The properties must contain the fully qualified name of the class followed by the method name, separated by a period ..
The method must be static and have a signature of either (String, Headers) or (String).
A ToFromStringSerde is also provided, for use with Kafka Streams.
JSON
Spring for Apache Kafka also provides JsonSerializer and JsonDeserializer implementations that are based on the
Jackson JSON object mapper.
The JsonSerializer allows writing any Java object as a JSON byte[].
The JsonDeserializer requires an additional Class<?> targetType argument to allow the deserialization of a consumed byte[] to the proper target object.
The following example shows how to create a JsonDeserializer:
JsonDeserializer<Thing> thingDeserializer = new JsonDeserializer<>(Thing.class);
You can customize both JsonSerializer and JsonDeserializer with an ObjectMapper.
You can also extend them to implement some particular configuration logic in the configure(Map<String, ?> configs, boolean isKey) method.
Starting with version 2.3, all the JSON-aware components are configured by default with a JacksonUtils.enhancedObjectMapper() instance, which comes with the MapperFeature.DEFAULT_VIEW_INCLUSION and DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES features disabled.
Also such an instance is supplied with well-known modules for custom data types, such a Java time and Kotlin support.
See JacksonUtils.enhancedObjectMapper() JavaDocs for more information.
This method also registers a org.springframework.kafka.support.JacksonMimeTypeModule for org.springframework.util.MimeType objects serialization into the plain string for inter-platform compatibility over the network.
A JacksonMimeTypeModule can be registered as a bean in the application context and it will be auto-configured into the Spring Boot ObjectMapper instance.
Also starting with version 2.3, the JsonDeserializer provides TypeReference-based constructors for better handling of target generic container types.
Starting with version 2.1, you can convey type information in record Headers, allowing the handling of multiple types.
In addition, you can configure the serializer and deserializer by using the following Kafka properties.
They have no effect if you have provided Serializer and Deserializer instances for KafkaConsumer and KafkaProducer, respectively.
Configuration Properties
-
JsonSerializer.ADD_TYPE_INFO_HEADERS(defaulttrue): You can set it tofalseto disable this feature on theJsonSerializer(sets theaddTypeInfoproperty). -
JsonSerializer.TYPE_MAPPINGS(defaultempty): See Mapping Types. -
JsonDeserializer.USE_TYPE_INFO_HEADERS(defaulttrue): You can set it tofalseto ignore headers set by the serializer. -
JsonDeserializer.REMOVE_TYPE_INFO_HEADERS(defaulttrue): You can set it tofalseto retain headers set by the serializer. -
JsonDeserializer.KEY_DEFAULT_TYPE: Fallback type for deserialization of keys if no header information is present. -
JsonDeserializer.VALUE_DEFAULT_TYPE: Fallback type for deserialization of values if no header information is present. -
JsonDeserializer.TRUSTED_PACKAGES(defaultjava.util,java.lang): Comma-delimited list of package patterns allowed for deserialization.*means deserialize all. -
JsonDeserializer.TYPE_MAPPINGS(defaultempty): See Mapping Types. -
JsonDeserializer.KEY_TYPE_METHOD(defaultempty): See Using Methods to Determine Types. -
JsonDeserializer.VALUE_TYPE_METHOD(defaultempty): See Using Methods to Determine Types.
Starting with version 2.2, the type information headers (if added by the serializer) are removed by the deserializer.
You can revert to the previous behavior by setting the removeTypeHeaders property to false, either directly on the deserializer or with the configuration property described earlier.
Starting with version 2.8, if you construct the serializer or deserializer programmatically as shown in Programmatic Construction, the above properties will be applied by the factories, as long as you have not set any properties explicitly (using set*() methods or using the fluent API).
Previously, when creating programmatically, the configuration properties were never applied; this is still the case if you explicitly set properties on the object directly.
|
Mapping Types
Starting with version 2.2, when using JSON, you can now provide type mappings by using the properties in the preceding list.
Previously, you had to customize the type mapper within the serializer and deserializer.
Mappings consist of a comma-delimited list of token:className pairs.
On outbound, the payload’s class name is mapped to the corresponding token.
On inbound, the token in the type header is mapped to the corresponding class name.
The following example creates a set of mappings:
senderProps.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, JsonSerializer.class);
senderProps.put(JsonSerializer.TYPE_MAPPINGS, "cat:com.mycat.Cat, hat:com.myhat.hat");
...
consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, JsonDeserializer.class);
consumerProps.put(JsonDeSerializer.TYPE_MAPPINGS, "cat:com.yourcat.Cat, hat:com.yourhat.hat");
| The corresponding objects must be compatible. |
If you use Spring Boot, you can provide these properties in the application.properties (or yaml) file.
The following example shows how to do so:
spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.properties.spring.json.type.mapping=cat:com.mycat.Cat,hat:com.myhat.Hat|
You can perform only simple configuration with properties.
For more advanced configuration (such as using a custom Setters are also provided, as an alternative to using these constructors. |
Starting with version 2.2, you can explicitly configure the deserializer to use the supplied target type and ignore type information in headers by using one of the overloaded constructors that have a boolean useHeadersIfPresent (which is true by default).
The following example shows how to do so:
DefaultKafkaConsumerFactory<Integer, Cat1> cf = new DefaultKafkaConsumerFactory<>(props,
new IntegerDeserializer(), new JsonDeserializer<>(Cat1.class, false));
Using Methods to Determine Types
Starting with version 2.5, you can now configure the deserializer, via properties, to invoke a method to determine the target type.
If present, this will override any of the other techniques discussed above.
This can be useful if the data is published by an application that does not use the Spring serializer and you need to deserialize to different types depending on the data, or other headers.
Set these properties to the method name - a fully qualified class name followed by the method name, separated by a period ..
The method must be declared as public static, have one of three signatures (String topic, byte[] data, Headers headers), (byte[] data, Headers headers) or (byte[] data) and return a Jackson JavaType.
-
JsonDeserializer.KEY_TYPE_METHOD:spring.json.key.type.method -
JsonDeserializer.VALUE_TYPE_METHOD:spring.json.value.type.method
You can use arbitrary headers or inspect the data to determine the type.
JavaType thing1Type = TypeFactory.defaultInstance().constructType(Thing1.class);
JavaType thing2Type = TypeFactory.defaultInstance().constructType(Thing2.class);
public static JavaType thingOneOrThingTwo(byte[] data, Headers headers) {
// {"thisIsAFieldInThing1":"value", ...
if (data[21] == '1') {
return thing1Type;
}
else {
return thing2Type;
}
}
For more sophisticated data inspection consider using JsonPath or similar but, the simpler the test to determine the type, the more efficient the process will be.
The following is an example of creating the deserializer programmatically (when providing the consumer factory with the deserializer in the constructor):
JsonDeserializer<Object> deser = new JsonDeserializer<>()
.trustedPackages("*")
.typeResolver(SomeClass::thing1Thing2JavaTypeForTopic);
...
public static JavaType thing1Thing2JavaTypeForTopic(String topic, byte[] data, Headers headers) {
...
}
Programmatic Construction
When constructing the serializer/deserializer programmatically for use in the producer/consumer factory, since version 2.3, you can use the fluent API, which simplifies configuration.
@Bean
public ProducerFactory<MyKeyType, MyValueType> pf() {
Map<String, Object> props = new HashMap<>();
// props.put(..., ...)
// ...
DefaultKafkaProducerFactory<MyKeyType, MyValueType> pf = new DefaultKafkaProducerFactory<>(props,
new JsonSerializer<MyKeyType>()
.forKeys()
.noTypeInfo(),
new JsonSerializer<MyValueType>()
.noTypeInfo());
return pf;
}
@Bean
public ConsumerFactory<MyKeyType, MyValueType> cf() {
Map<String, Object> props = new HashMap<>();
// props.put(..., ...)
// ...
DefaultKafkaConsumerFactory<MyKeyType, MyValueType> cf = new DefaultKafkaConsumerFactory<>(props,
new JsonDeserializer<>(MyKeyType.class)
.forKeys()
.ignoreTypeHeaders(),
new JsonDeserializer<>(MyValueType.class)
.ignoreTypeHeaders());
return cf;
}
To provide type mapping programmatically, similar to Using Methods to Determine Types, use the typeFunction property.
JsonDeserializer<Object> deser = new JsonDeserializer<>()
.trustedPackages("*")
.typeFunction(MyUtils::thingOneOrThingTwo);
Alternatively, as long as you don’t use the fluent API to configure properties, or set them using set*() methods, the factories will configure the serializer/deserializer using the configuration properties; see Configuration Properties.
Delegating Serializer and Deserializer
Using Headers
Version 2.3 introduced the DelegatingSerializer and DelegatingDeserializer, which allow producing and consuming records with different key and/or value types.
Producers must set a header DelegatingSerializer.VALUE_SERIALIZATION_SELECTOR to a selector value that is used to select which serializer to use for the value and DelegatingSerializer.KEY_SERIALIZATION_SELECTOR for the key; if a match is not found, an IllegalStateException is thrown.
For incoming records, the deserializer uses the same headers to select the deserializer to use; if a match is not found or the header is not present, the raw byte[] is returned.
You can configure the map of selector to Serializer / Deserializer via a constructor, or you can configure it via Kafka producer/consumer properties with the keys DelegatingSerializer.VALUE_SERIALIZATION_SELECTOR_CONFIG and DelegatingSerializer.KEY_SERIALIZATION_SELECTOR_CONFIG.
For the serializer, the producer property can be a Map<String, Object> where the key is the selector and the value is a Serializer instance, a serializer Class or the class name.
The property can also be a String of comma-delimited map entries, as shown below.
For the deserializer, the consumer property can be a Map<String, Object> where the key is the selector and the value is a Deserializer instance, a deserializer Class or the class name.
The property can also be a String of comma-delimited map entries, as shown below.
To configure using properties, use the following syntax:
producerProps.put(DelegatingSerializer.VALUE_SERIALIZATION_SELECTOR_CONFIG,
"thing1:com.example.MyThing1Serializer, thing2:com.example.MyThing2Serializer")
consumerProps.put(DelegatingDeserializer.VALUE_SERIALIZATION_SELECTOR_CONFIG,
"thing1:com.example.MyThing1Deserializer, thing2:com.example.MyThing2Deserializer")
Producers would then set the DelegatingSerializer.VALUE_SERIALIZATION_SELECTOR header to thing1 or thing2.
This technique supports sending different types to the same topic (or different topics).
Starting with version 2.5.1, it is not necessary to set the selector header, if the type (key or value) is one of the standard types supported by Serdes (Long, Integer, etc).
Instead, the serializer will set the header to the class name of the type.
It is not necessary to configure serializers or deserializers for these types, they will be created (once) dynamically.
|
For another technique to send different types to different topics, see Using RoutingKafkaTemplate.
By Type
Version 2.8 introduced the DelegatingByTypeSerializer.
@Bean
public ProducerFactory<Integer, Object> producerFactory(Map<String, Object> config) {
return new DefaultKafkaProducerFactory<>(config,
null, new DelegatingByTypeSerializer(Map.of(
byte[].class, new ByteArraySerializer(),
Bytes.class, new BytesSerializer(),
String.class, new StringSerializer())));
}
Starting with version 2.8.3, you can configure the serializer to check if the map key is assignable from the target object, useful when a delegate serializer can serialize sub classes.
In this case, if there are amiguous matches, an ordered Map, such as a LinkedHashMap should be provided.
By Topic
Starting with version 2.8, the DelegatingByTopicSerializer and DelegatingByTopicDeserializer allow selection of a serializer/deserializer based on the topic name.
Regex Pattern s are used to lookup the instance to use.
The map can be configured using a constructor, or via properties (a comma delimited list of pattern:serializer).
producerConfigs.put(DelegatingByTopicSerializer.VALUE_SERIALIZATION_TOPIC_CONFIG,
"topic[0-4]:" + ByteArraySerializer.class.getName()
+ ", topic[5-9]:" + StringSerializer.class.getName());
...
ConsumerConfigs.put(DelegatingByTopicDeserializer.VALUE_SERIALIZATION_TOPIC_CONFIG,
"topic[0-4]:" + ByteArrayDeserializer.class.getName()
+ ", topic[5-9]:" + StringDeserializer.class.getName());
Use KEY_SERIALIZATION_TOPIC_CONFIG when using this for keys.
@Bean
public ProducerFactory<Integer, Object> producerFactory(Map<String, Object> config) {
return new DefaultKafkaProducerFactory<>(config,
new IntegerSerializer(),
new DelegatingByTopicSerializer(Map.of(
Pattern.compile("topic[0-4]"), new ByteArraySerializer(),
Pattern.compile("topic[5-9]"), new StringSerializer())),
new JsonSerializer<Object>()); // default
}
You can specify a default serializer/deserializer to use when there is no pattern match using DelegatingByTopicSerialization.KEY_SERIALIZATION_TOPIC_DEFAULT and DelegatingByTopicSerialization.VALUE_SERIALIZATION_TOPIC_DEFAULT.
An additional property DelegatingByTopicSerialization.CASE_SENSITIVE (default true), when set to false makes the topic lookup case insensitive.
Retrying Deserializer
The RetryingDeserializer uses a delegate Deserializer and RetryTemplate to retry deserialization when the delegate might have transient errors, such a network issues, during deserialization.
ConsumerFactory cf = new DefaultKafkaConsumerFactory(myConsumerConfigs,
new RetryingDeserializer(myUnreliableKeyDeserializer, retryTemplate),
new RetryingDeserializer(myUnreliableValueDeserializer, retryTemplate));
Refer to the spring-retry project for configuration of the RetryTemplate with a retry policy, back off policy, etc.
Spring Messaging Message Conversion
Although the Serializer and Deserializer API is quite simple and flexible from the low-level Kafka Consumer and Producer perspective, you might need more flexibility at the Spring Messaging level, when using either @KafkaListener or Spring Integration’s Apache Kafka Support.
To let you easily convert to and from org.springframework.messaging.Message, Spring for Apache Kafka provides a MessageConverter abstraction with the MessagingMessageConverter implementation and its JsonMessageConverter (and subclasses) customization.
You can inject the MessageConverter into a KafkaTemplate instance directly and by using AbstractKafkaListenerContainerFactory bean definition for the @KafkaListener.containerFactory() property.
The following example shows how to do so:
@Bean
public KafkaListenerContainerFactory<?> kafkaJsonListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setRecordMessageConverter(new JsonMessageConverter());
return factory;
}
...
@KafkaListener(topics = "jsonData",
containerFactory = "kafkaJsonListenerContainerFactory")
public void jsonListener(Cat cat) {
...
}
When using Spring Boot, simply define the converter as a @Bean and Spring Boot auto configuration will wire it into the auto-configured template and container factory.
When you use a @KafkaListener, the parameter type is provided to the message converter to assist with the conversion.
|
This type inference can be achieved only when the |
|
On the consumer side, you can configure a On the producer side, when you use Spring Integration or the
Again, using For convenience, starting with version 2.3, the framework also provides a |
Starting with version 2.7.1, message payload conversion can be delegated to a spring-messaging SmartMessageConverter; this enables conversion, for example, to be based on the MessageHeaders.CONTENT_TYPE header.
The KafkaMessageConverter.fromMessage() method is called for outbound conversion to a ProducerRecord with the message payload in the ProducerRecord.value() property.
The KafkaMessageConverter.toMessage() method is called for inbound conversion from ConsumerRecord with the payload being the ConsumerRecord.value() property.
The SmartMessageConverter.toMessage() method is called to create a new outbound Message<?> from the Message passed to`fromMessage()` (usually by KafkaTemplate.send(Message<?> msg)).
Similarly, in the KafkaMessageConverter.toMessage() method, after the converter has created a new Message<?> from the ConsumerRecord, the SmartMessageConverter.fromMessage() method is called and then the final inbound message is created with the newly converted payload.
In either case, if the SmartMessageConverter returns null, the original message is used.
|
When the default converter is used in the KafkaTemplate and listener container factory, you configure the SmartMessageConverter by calling setMessagingConverter() on the template and via the contentMessageConverter property on @KafkaListener methods.
Examples:
template.setMessagingConverter(mySmartConverter);
@KafkaListener(id = "withSmartConverter", topics = "someTopic",
contentTypeConverter = "mySmartConverter")
public void smart(Thing thing) {
...
}
Using Spring Data Projection Interfaces
Starting with version 2.1.1, you can convert JSON to a Spring Data Projection interface instead of a concrete type. This allows very selective, and low-coupled bindings to data, including the lookup of values from multiple places inside the JSON document. For example the following interface can be defined as message payload type:
interface SomeSample {
@JsonPath({ "$.username", "$.user.name" })
String getUsername();
}
@KafkaListener(id="projection.listener", topics = "projection")
public void projection(SomeSample in) {
String username = in.getUsername();
...
}
Accessor methods will be used to lookup the property name as field in the received JSON document by default.
The @JsonPath expression allows customization of the value lookup, and even to define multiple JSON Path expressions, to lookup values from multiple places until an expression returns an actual value.
To enable this feature, use a ProjectingMessageConverter configured with an appropriate delegate converter (used for outbound conversion and converting non-projection interfaces).
You must also add spring-data:spring-data-commons and com.jayway.jsonpath:json-path to the class path.
When used as the parameter to a @KafkaListener method, the interface type is automatically passed to the converter as normal.
Using ErrorHandlingDeserializer
When a deserializer fails to deserialize a message, Spring has no way to handle the problem, because it occurs before the poll() returns.
To solve this problem, the ErrorHandlingDeserializer has been introduced.
This deserializer delegates to a real deserializer (key or value).
If the delegate fails to deserialize the record content, the ErrorHandlingDeserializer returns a null value and a DeserializationException in a header that contains the cause and the raw bytes.
When you use a record-level MessageListener, if the ConsumerRecord contains a DeserializationException header for either the key or value, the container’s ErrorHandler is called with the failed ConsumerRecord.
The record is not passed to the listener.
Alternatively, you can configure the ErrorHandlingDeserializer to create a custom value by providing a failedDeserializationFunction, which is a Function<FailedDeserializationInfo, T>.
This function is invoked to create an instance of T, which is passed to the listener in the usual fashion.
An object of type FailedDeserializationInfo, which contains all the contextual information is provided to the function.
You can find the DeserializationException (as a serialized Java object) in headers.
See the Javadoc for the ErrorHandlingDeserializer for more information.
You can use the DefaultKafkaConsumerFactory constructor that takes key and value Deserializer objects and wire in appropriate ErrorHandlingDeserializer instances that you have configured with the proper delegates.
Alternatively, you can use consumer configuration properties (which are used by the ErrorHandlingDeserializer) to instantiate the delegates.
The property names are ErrorHandlingDeserializer.KEY_DESERIALIZER_CLASS and ErrorHandlingDeserializer.VALUE_DESERIALIZER_CLASS.
The property value can be a class or class name.
The following example shows how to set these properties:
... // other props
props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ErrorHandlingDeserializer.class);
props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, ErrorHandlingDeserializer.class);
props.put(ErrorHandlingDeserializer.KEY_DESERIALIZER_CLASS, JsonDeserializer.class);
props.put(JsonDeserializer.KEY_DEFAULT_TYPE, "com.example.MyKey")
props.put(ErrorHandlingDeserializer.VALUE_DESERIALIZER_CLASS, JsonDeserializer.class.getName());
props.put(JsonDeserializer.VALUE_DEFAULT_TYPE, "com.example.MyValue")
props.put(JsonDeserializer.TRUSTED_PACKAGES, "com.example")
return new DefaultKafkaConsumerFactory<>(props);
The following example uses a failedDeserializationFunction.
public class BadFoo extends Foo {
private final FailedDeserializationInfo failedDeserializationInfo;
public BadFoo(FailedDeserializationInfo failedDeserializationInfo) {
this.failedDeserializationInfo = failedDeserializationInfo;
}
public FailedDeserializationInfo getFailedDeserializationInfo() {
return this.failedDeserializationInfo;
}
}
public class FailedFooProvider implements Function<FailedDeserializationInfo, Foo> {
@Override
public Foo apply(FailedDeserializationInfo info) {
return new BadFoo(info);
}
}
The preceding example uses the following configuration:
...
consumerProps.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ErrorHandlingDeserializer.class);
consumerProps.put(ErrorHandlingDeserializer.VALUE_DESERIALIZER_CLASS, JsonDeserializer.class);
consumerProps.put(ErrorHandlingDeserializer.VALUE_FUNCTION, FailedFooProvider.class);
...
If the consumer is configured with an ErrorHandlingDeserializer it is important to configure the KafkaTemplate and its producer with a serializer that can handle normal objects as well as raw byte[] values, which result from deserialization exceptions.
The generic value type of the template should be Object.
One technique is to use the DelegatingByTypeSerializer; an example follows:
|
@Bean
public ProducerFactory<String, Object> producerFactory() {
return new DefaultKafkaProducerFactory<>(producerConfiguration(), new StringSerializer(),
new DelegatingByTypeSerializer(Map.of(byte[].class, new ByteArraySerializer(),
MyNormalObject.class, new JsonSerializer<Object>())));
}
@Bean
public KafkaTemplate<String, Object> kafkaTemplate() {
return new KafkaTemplate<>(producerFactory());
}
When using an ErrorHandlingDeserializer with a batch listener, you must check for the deserialization exceptions in message headers.
When used with a DefaultBatchErrorHandler, you can use that header to determine which record the exception failed on and communicate to the error handler via a BatchListenerFailedException.
@KafkaListener(id = "test", topics = "test")
void listen(List<Thing> in, @Header(KafkaHeaders.BATCH_CONVERTED_HEADERS) List<Map<String, Object>> headers) {
for (int i = 0; i < in.size(); i++) {
Thing thing = in.get(i);
if (thing == null
&& headers.get(i).get(SerializationUtils.VALUE_DESERIALIZER_EXCEPTION_HEADER) != null) {
try {
DeserializationException deserEx = SerializationUtils.byteArrayToDeserializationException(this.logger,
headers.get(i).get(SerializationUtils.VALUE_DESERIALIZER_EXCEPTION_HEADER));
if (deserEx != null) {
logger.error(deserEx, "Record at index " + i + " could not be deserialized");
}
}
catch (Exception ex) {
logger.error(ex, "Record at index " + i + " could not be deserialized");
}
throw new BatchListenerFailedException("Deserialization", deserEx, i);
}
process(thing);
}
}
SerializationUtils.byteArrayToDeserializationException() can be used to convert the header to a DeserializationException.
When consuming List<ConsumerRecord<?, ?>, SerializationUtils.getExceptionFromHeader() is used instead:
@KafkaListener(id = "kgh2036", topics = "kgh2036")
void listen(List<ConsumerRecord<String, Thing>> in) {
for (int i = 0; i < in.size(); i++) {
ConsumerRecord<String, Thing> rec = in.get(i);
if (rec.value() == null) {
DeserializationException deserEx = SerializationUtils.getExceptionFromHeader(rec,
SerializationUtils.VALUE_DESERIALIZER_EXCEPTION_HEADER, this.logger);
if (deserEx != null) {
logger.error(deserEx, "Record at offset " + rec.offset() + " could not be deserialized");
throw new BatchListenerFailedException("Deserialization", deserEx, i);
}
}
process(rec.value());
}
}
If you are also using a DeadLetterPublishingRecoverer, the record published for a DeserializationException will have a record.value() of type byte[]; this should not be serialized.
Consider using a DelegatingByTypeSerializer configured to use a ByteArraySerializer for byte[] and the normal serializer (Json, Avro, etc) for all other types.
|
Payload Conversion with Batch Listeners
You can also use a JsonMessageConverter within a BatchMessagingMessageConverter to convert batch messages when you use a batch listener container factory.
See Serialization, Deserialization, and Message Conversion and Spring Messaging Message Conversion for more information.
By default, the type for the conversion is inferred from the listener argument.
If you configure the JsonMessageConverter with a DefaultJackson2TypeMapper that has its TypePrecedence set to TYPE_ID (instead of the default INFERRED), the converter uses the type information in headers (if present) instead.
This allows, for example, listener methods to be declared with interfaces instead of concrete classes.
Also, the type converter supports mapping, so the deserialization can be to a different type than the source (as long as the data is compatible).
This is also useful when you use class-level @KafkaListener instances where the payload must have already been converted to determine which method to invoke.
The following example creates beans that use this method:
@Bean
public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
factory.setConsumerFactory(consumerFactory());
factory.setBatchListener(true);
factory.setBatchMessageConverter(new BatchMessagingMessageConverter(converter()));
return factory;
}
@Bean
public JsonMessageConverter converter() {
return new JsonMessageConverter();
}
Note that, for this to work, the method signature for the conversion target must be a container object with a single generic parameter type, such as the following:
@KafkaListener(topics = "blc1")
public void listen(List<Foo> foos, @Header(KafkaHeaders.OFFSET) List<Long> offsets) {
...
}
Note that you can still access the batch headers.
If the batch converter has a record converter that supports it, you can also receive a list of messages where the payloads are converted according to the generic type. The following example shows how to do so:
@KafkaListener(topics = "blc3", groupId = "blc3")
public void listen1(List<Message<Foo>> fooMessages) {
...
}
ConversionService Customization
Starting with version 2.1.1, the org.springframework.core.convert.ConversionService used by the default o.s.messaging.handler.annotation.support.MessageHandlerMethodFactory to resolve parameters for the invocation of a listener method is supplied with all beans that implement any of the following interfaces:
-
org.springframework.core.convert.converter.Converter -
org.springframework.core.convert.converter.GenericConverter -
org.springframework.format.Formatter
This lets you further customize listener deserialization without changing the default configuration for ConsumerFactory and KafkaListenerContainerFactory.
Setting a custom MessageHandlerMethodFactory on the KafkaListenerEndpointRegistrar through a KafkaListenerConfigurer bean disables this feature.
|
Adding custom HandlerMethodArgumentResolver to @KafkaListener
Starting with version 2.4.2 you are able to add your own HandlerMethodArgumentResolver and resolve custom method parameters.
All you need is to implement KafkaListenerConfigurer and use method setCustomMethodArgumentResolvers() from class KafkaListenerEndpointRegistrar.
@Configuration
class CustomKafkaConfig implements KafkaListenerConfigurer {
@Override
public void configureKafkaListeners(KafkaListenerEndpointRegistrar registrar) {
registrar.setCustomMethodArgumentResolvers(
new HandlerMethodArgumentResolver() {
@Override
public boolean supportsParameter(MethodParameter parameter) {
return CustomMethodArgument.class.isAssignableFrom(parameter.getParameterType());
}
@Override
public Object resolveArgument(MethodParameter parameter, Message<?> message) {
return new CustomMethodArgument(
message.getHeaders().get(KafkaHeaders.RECEIVED_TOPIC, String.class)
);
}
}
);
}
}
You can also completely replace the framework’s argument resolution by adding a custom MessageHandlerMethodFactory to the KafkaListenerEndpointRegistrar bean.
If you do this, and your application needs to handle tombstone records, with a null value() (e.g. from a compacted topic), you should add a KafkaNullAwarePayloadArgumentResolver to the factory; it must be the last resolver because it supports all types and can match arguments without a @Payload annotation.
If you are using a DefaultMessageHandlerMethodFactory, set this resolver as the last custom resolver; the factory will ensure that this resolver will be used before the standard PayloadMethodArgumentResolver, which has no knowledge of KafkaNull payloads.
4.1.20. Message Headers
The 0.11.0.0 client introduced support for headers in messages.
As of version 2.0, Spring for Apache Kafka now supports mapping these headers to and from spring-messaging MessageHeaders.
Previous versions mapped ConsumerRecord and ProducerRecord to spring-messaging Message<?>, where the value property is mapped to and from the payload and other properties (topic, partition, and so on) were mapped to headers.
This is still the case, but additional (arbitrary) headers can now be mapped.
|
Apache Kafka headers have a simple API, shown in the following interface definition:
public interface Header {
String key();
byte[] value();
}
The KafkaHeaderMapper strategy is provided to map header entries between Kafka Headers and MessageHeaders.
Its interface definition is as follows:
public interface KafkaHeaderMapper {
void fromHeaders(MessageHeaders headers, Headers target);
void toHeaders(Headers source, Map<String, Object> target);
}
The SimpleKafkaHeaderMapper maps raw headers as byte[], with configuration options for conversion to String values.
The DefaultKafkaHeaderMapper maps the key to the MessageHeaders header name and, in order to support rich header types for outbound messages, JSON conversion is performed.
A “special” header (with a key of spring_json_header_types) contains a JSON map of <key>:<type>.
This header is used on the inbound side to provide appropriate conversion of each header value to the original type.
On the inbound side, all Kafka Header instances are mapped to MessageHeaders.
On the outbound side, by default, all MessageHeaders are mapped, except id, timestamp, and the headers that map to ConsumerRecord properties.
You can specify which headers are to be mapped for outbound messages, by providing patterns to the mapper. The following listing shows a number of example mappings:
public DefaultKafkaHeaderMapper() { (1)
...
}
public DefaultKafkaHeaderMapper(ObjectMapper objectMapper) { (2)
...
}
public DefaultKafkaHeaderMapper(String... patterns) { (3)
...
}
public DefaultKafkaHeaderMapper(ObjectMapper objectMapper, String... patterns) { (4)
...
}
| 1 | Uses a default Jackson ObjectMapper and maps most headers, as discussed before the example. |
| 2 | Uses the provided Jackson ObjectMapper and maps most headers, as discussed before the example. |
| 3 | Uses a default Jackson ObjectMapper and maps headers according to the provided patterns. |
| 4 | Uses the provided Jackson ObjectMapper and maps headers according to the provided patterns. |
Patterns are rather simple and can contain a leading wildcard (), a trailing wildcard, or both (for example, .cat.*).
You can negate patterns with a leading !.
The first pattern that matches a header name (whether positive or negative) wins.
When you provide your own patterns, we recommend including !id and !timestamp, since these headers are read-only on the inbound side.
By default, the mapper deserializes only classes in java.lang and java.util.
You can trust other (or all) packages by adding trusted packages with the addTrustedPackages method.
If you receive messages from untrusted sources, you may wish to add only those packages you trust.
To trust all packages, you can use mapper.addTrustedPackages("*").
|
Mapping String header values in a raw form is useful when communicating with systems that are not aware of the mapper’s JSON format.
|
Starting with version 2.2.5, you can specify that certain string-valued headers should not be mapped using JSON, but to/from a raw byte[].
The AbstractKafkaHeaderMapper has new properties; mapAllStringsOut when set to true, all string-valued headers will be converted to byte[] using the charset property (default UTF-8).
In addition, there is a property rawMappedHeaders, which is a map of header name : boolean; if the map contains a header name, and the header contains a String value, it will be mapped as a raw byte[] using the charset.
This map is also used to map raw incoming byte[] headers to String using the charset if, and only if, the boolean in the map value is true.
If the boolean is false, or the header name is not in the map with a true value, the incoming header is simply mapped as the raw unmapped header.
The following test case illustrates this mechanism.
@Test
public void testSpecificStringConvert() {
DefaultKafkaHeaderMapper mapper = new DefaultKafkaHeaderMapper();
Map<String, Boolean> rawMappedHeaders = new HashMap<>();
rawMappedHeaders.put("thisOnesAString", true);
rawMappedHeaders.put("thisOnesBytes", false);
mapper.setRawMappedHeaders(rawMappedHeaders);
Map<String, Object> headersMap = new HashMap<>();
headersMap.put("thisOnesAString", "thing1");
headersMap.put("thisOnesBytes", "thing2");
headersMap.put("alwaysRaw", "thing3".getBytes());
MessageHeaders headers = new MessageHeaders(headersMap);
Headers target = new RecordHeaders();
mapper.fromHeaders(headers, target);
assertThat(target).containsExactlyInAnyOrder(
new RecordHeader("thisOnesAString", "thing1".getBytes()),
new RecordHeader("thisOnesBytes", "thing2".getBytes()),
new RecordHeader("alwaysRaw", "thing3".getBytes()));
headersMap.clear();
mapper.toHeaders(target, headersMap);
assertThat(headersMap).contains(
entry("thisOnesAString", "thing1"),
entry("thisOnesBytes", "thing2".getBytes()),
entry("alwaysRaw", "thing3".getBytes()));
}
Both header mappers map all inbound headers, by default. Starting with version 2.8.8, the patterns, can also applied to inbound mapping. To create a mapper for inbound mapping, use one of the static methods on the respective mapper:
public static DefaultKafkaHeaderMapper forInboundOnlyWithMatchers(String... patterns) {
}
public static DefaultKafkaHeaderMapper forInboundOnlyWithMatchers(ObjectMapper objectMapper, String... patterns) {
}
public static SimpleKafkaHeaderMapper forInboundOnlyWithMatchers(String... patterns) {
}
For example:
DefaultKafkaHeaderMapper inboundMapper = DefaultKafkaHeaderMapper.forInboundOnlyWithMatchers("!abc*", "*");
This will exclude all headers beginning with abc and include all others.
By default, the DefaultKafkaHeaderMapper is used in the MessagingMessageConverter and BatchMessagingMessageConverter, as long as Jackson is on the class path.
With the batch converter, the converted headers are available in the KafkaHeaders.BATCH_CONVERTED_HEADERS as a List<Map<String, Object>> where the map in a position of the list corresponds to the data position in the payload.
If there is no converter (either because Jackson is not present or it is explicitly set to null), the headers from the consumer record are provided unconverted in the KafkaHeaders.NATIVE_HEADERS header.
This header is a Headers object (or a List<Headers> in the case of the batch converter), where the position in the list corresponds to the data position in the payload).
Certain types are not suitable for JSON serialization, and a simple toString() serialization might be preferred for these types.
The DefaultKafkaHeaderMapper has a method called addToStringClasses() that lets you supply the names of classes that should be treated this way for outbound mapping.
During inbound mapping, they are mapped as String.
By default, only org.springframework.util.MimeType and org.springframework.http.MediaType are mapped this way.
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Starting with version 2.3, handling of String-valued headers is simplified.
Such headers are no longer JSON encoded, by default (i.e. they do not have enclosing "…" added).
The type is still added to the JSON_TYPES header so the receiving system can convert back to a String (from byte[]).
The mapper can handle (decode) headers produced by older versions (it checks for a leading "); in this way an application using 2.3 can consume records from older versions.
|
To be compatible with earlier versions, set encodeStrings to true, if records produced by a version using 2.3 might be consumed by applications using earlier versions.
When all applications are using 2.3 or higher, you can leave the property at its default value of false.
|
@Bean
MessagingMessageConverter converter() {
MessagingMessageConverter converter = new MessagingMessageConverter();
DefaultKafkaHeaderMapper mapper = new DefaultKafkaHeaderMapper();
mapper.setEncodeStrings(true);
converter.setHeaderMapper(mapper);
return converter;
}
If using Spring Boot, it will auto configure this converter bean into the auto-configured KafkaTemplate; otherwise you should add this converter to the template.
4.1.21. Null Payloads and Log Compaction of 'Tombstone' Records
When you use Log Compaction, you can send and receive messages with null payloads to identify the deletion of a key.
You can also receive null values for other reasons, such as a Deserializer that might return null when it cannot deserialize a value.
To send a null payload by using the KafkaTemplate, you can pass null into the value argument of the send() methods.
One exception to this is the send(Message<?> message) variant.
Since spring-messaging Message<?> cannot have a null payload, you can use a special payload type called KafkaNull, and the framework sends null.
For convenience, the static KafkaNull.INSTANCE is provided.
When you use a message listener container, the received ConsumerRecord has a null value().
To configure the @KafkaListener to handle null payloads, you must use the @Payload annotation with required = false.
If it is a tombstone message for a compacted log, you usually also need the key so that your application can determine which key was “deleted”.
The following example shows such a configuration:
@KafkaListener(id = "deletableListener", topics = "myTopic")
public void listen(@Payload(required = false) String value, @Header(KafkaHeaders.RECEIVED_KEY) String key) {
// value == null represents key deletion
}
When you use a class-level @KafkaListener with multiple @KafkaHandler methods, some additional configuration is needed.
Specifically, you need a @KafkaHandler method with a KafkaNull payload.
The following example shows how to configure one:
@KafkaListener(id = "multi", topics = "myTopic")
static class MultiListenerBean {
@KafkaHandler
public void listen(String cat) {
...
}
@KafkaHandler
public void listen(Integer hat) {
...
}
@KafkaHandler
public void delete(@Payload(required = false) KafkaNull nul, @Header(KafkaHeaders.RECEIVED_KEY) int key) {
...
}
}
Note that the argument is null, not KafkaNull.
This feature requires the use of a KafkaNullAwarePayloadArgumentResolver which the framework will configure when using the default MessageHandlerMethodFactory.
When using a custom MessageHandlerMethodFactory, see Adding custom HandlerMethodArgumentResolver to @KafkaListener.
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4.1.22. Handling Exceptions
This section describes how to handle various exceptions that may arise when you use Spring for Apache Kafka.
Listener Error Handlers
Starting with version 2.0, the @KafkaListener annotation has a new attribute: errorHandler.
You can use the errorHandler to provide the bean name of a KafkaListenerErrorHandler implementation.
This functional interface has one method, as the following listing shows:
@FunctionalInterface
public interface KafkaListenerErrorHandler {
Object handleError(Message<?> message, ListenerExecutionFailedException exception) throws Exception;
}
You have access to the spring-messaging Message<?> object produced by the message converter and the exception that was thrown by the listener, which is wrapped in a ListenerExecutionFailedException.
The error handler can throw the original or a new exception, which is thrown to the container.
Anything returned by the error handler is ignored.
Starting with version 2.7, you can set the rawRecordHeader property on the MessagingMessageConverter and BatchMessagingMessageConverter which causes the raw ConsumerRecord to be added to the converted Message<?> in the KafkaHeaders.RAW_DATA header.
This is useful, for example, if you wish to use a DeadLetterPublishingRecoverer in a listener error handler.
It might be used in a request/reply scenario where you wish to send a failure result to the sender, after some number of retries, after capturing the failed record in a dead letter topic.
@Bean
KafkaListenerErrorHandler eh(DeadLetterPublishingRecoverer recoverer) {
return (msg, ex) -> {
if (msg.getHeaders().get(KafkaHeaders.DELIVERY_ATTEMPT, Integer.class) > 9) {
recoverer.accept(msg.getHeaders().get(KafkaHeaders.RAW_DATA, ConsumerRecord.class), ex);
return "FAILED";
}
throw ex;
};
}
It has a sub-interface (ConsumerAwareListenerErrorHandler) that has access to the consumer object, through the following method:
Object handleError(Message<?> message, ListenerExecutionFailedException exception, Consumer<?, ?> consumer);
Another sub-interface (ManualAckListenerErrorHandler) provides access to the Acknowledgment object when using manual AckMode s.
Object handleError(Message<?> message, ListenerExecutionFailedException exception,
Consumer<?, ?> consumer, @Nullable Acknowledgment ack);
In either case, you should NOT perform any seeks on the consumer because the container would be unaware of them.
Container Error Handlers
Starting with version 2.8, the legacy ErrorHandler and BatchErrorHandler interfaces have been superseded by a new CommonErrorHandler.
These error handlers can handle errors for both record and batch listeners, allowing a single listener container factory to create containers for both types of listener.
CommonErrorHandler implementations to replace most legacy framework error handler implementations are provided and the legacy error handlers deprecated.
The legacy interfaces are still supported by listener containers and listener container factories; they will be deprecated in a future release.
See Migrating Custom Legacy Error Handler Implementations to CommonErrorHandler for information to migrate custom error handlers to CommonErrorHandler.
When transactions are being used, no error handlers are configured, by default, so that the exception will roll back the transaction.
Error handling for transactional containers are handled by the AfterRollbackProcessor.
If you provide a custom error handler when using transactions, it must throw an exception if you want the transaction rolled back.
This interface has a default method isAckAfterHandle() which is called by the container to determine whether the offset(s) should be committed if the error handler returns without throwing an exception; it returns true by default.
Typically, the error handlers provided by the framework will throw an exception when the error is not "handled" (e.g. after performing a seek operation).
By default, such exceptions are logged by the container at ERROR level.
All of the framework error handlers extend KafkaExceptionLogLevelAware which allows you to control the level at which these exceptions are logged.
/**
* Set the level at which the exception thrown by this handler is logged.
* @param logLevel the level (default ERROR).
*/
public void setLogLevel(KafkaException.Level logLevel) {
...
}
You can specify a global error handler to be used for all listeners in the container factory. The following example shows how to do so:
@Bean
public KafkaListenerContainerFactory<ConcurrentMessageListenerContainer<Integer, String>>
kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
new ConcurrentKafkaListenerContainerFactory<>();
...
factory.setCommonErrorHandler(myErrorHandler);
...
return factory;
}
By default, if an annotated listener method throws an exception, it is thrown to the container, and the message is handled according to the container configuration.
The container commits any pending offset commits before calling the error handler.
If you are using Spring Boot, you simply need to add the error handler as a @Bean and Boot will add it to the auto-configured factory.
Back Off Handlers
Error handlers such as the DefaultErrorHandler use a BackOff to determine how long to wait before retrying a delivery.
Starting with version 2.9, you can configure a custom BackOffHandler.
The default handler simply suspends the thread until the back off time passes (or the container is stopped).
The framework also provides the ContainerPausingBackOffHandler which pauses the listener container until the back off time passes and then resumes the container.
This is useful when the delays are longer than the max.poll.interval.ms consumer property.
Note that the resolution of the actual back off time will be affected by the pollTimeout container property.
DefaultErrorHandler
This new error handler replaces the SeekToCurrentErrorHandler and RecoveringBatchErrorHandler, which have been the default error handlers for several releases now.
One difference is that the fallback behavior for batch listeners (when an exception other than a BatchListenerFailedException is thrown) is the equivalent of the Retrying Complete Batches.
Starting with version 2.9, the DefaultErrorHandler can be configured to provide the same semantics as seeking the unprocessed record offsets as discussed below, but without actually seeking.
Instead, the records are retained by the listener container and resubmitted to the listener after the error handler exits (and after performing a single paused poll(), to keep the consumer alive; if Non-Blocking Retries or a ContainerPausingBackOffHandler are being used, the pause may extend over multiple polls).
The error handler returns a result to the container that indicates whether the current failing record can be resubmitted, or if it was recovered and then it will not be sent to the listener again.
To enable this mode, set the property seekAfterError to false.
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The error handler can recover (skip) a record that keeps failing.
By default, after ten failures, the failed record is logged (at the ERROR level).
You can configure the handler with a custom recoverer (BiConsumer) and a BackOff that controls the delivery attempts and delays between each.
Using a FixedBackOff with FixedBackOff.UNLIMITED_ATTEMPTS causes (effectively) infinite retries.
The following example configures recovery after three tries:
DefaultErrorHandler errorHandler =
new DefaultErrorHandler((record, exception) -> {
// recover after 3 failures, with no back off - e.g. send to a dead-letter topic
}, new FixedBackOff(0L, 2L));
To configure the listener container with a customized instance of this handler, add it to the container factory.
For example, with the @KafkaListener container factory, you can add DefaultErrorHandler as follows:
@Bean
public ConcurrentKafkaListenerContainerFactory<String, String> kafkaListenerContainerFactory() {
ConcurrentKafkaListenerContainerFactory<String, String> factory = new ConcurrentKafkaListenerContainerFactory();
factory.setConsumerFactory(consumerFactory());
factory.getContainerProperties().setAckMode(AckMode.RECORD);
factory.setCommonErrorHandler(new DefaultErrorHandler(new FixedBackOff(1000L, 2L)));
return factory;
}
For a record listener, this will retry a delivery up to 2 times (3 delivery attempts) with a back off of 1 second, instead of the default configuration (FixedBackOff(0L, 9)).
Failures are simply logged after retries are exhausted.
As an example; if the poll returns six records (two from each partition 0, 1, 2) and the listener throws an exception on the fourth record, the container acknowledges the first three messages by committing their offsets.
The DefaultErrorHandler seeks to offset 1 for partition 1 and offset 0 for partition 2.
The next poll() returns the three unprocessed records.
If the AckMode was BATCH, the container commits the offsets for the first two partitions before calling the error handler.
For a batch listener, the listener must throw a BatchListenerFailedException indicating which records in the batch failed.
The sequence of events is:
-
Commit the offsets of the records before the index.
-
If retries are not exhausted, perform seeks so that all the remaining records (including the failed record) will be redelivered.
-
If retries are exhausted, attempt recovery of the failed record (default log only) and perform seeks so that the remaining records (excluding the failed record) will be redelivered. The recovered record’s offset is committed
-
If retries are exhausted and recovery fails, seeks are performed as if retries are not exhausted.
Starting with version 2.9, the DefaultErrorHandler can be configured to provide the same semantics as seeking the unprocessed record offsets as discussed above, but without actually seeking.
Instead, error handler creates a new ConsumerRecords<?, ?> containing just the unprocessed records which will then be submitted to the listener (after performing a single paused poll(), to keep the consumer alive).
To enable this mode, set the property seekAfterError to false.
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The default recoverer logs the failed record after retries are exhausted.
You can use a custom recoverer, or one provided by the framework such as the DeadLetterPublishingRecoverer.
When using a POJO batch listener (e.g. List<Thing>), and you don’t have the full consumer record to add to the exception, you can just add the index of the record that failed:
@KafkaListener(id = "recovering", topics = "someTopic")
public void listen(List<Thing> things) {
for (int i = 0; i < records.size(); i++) {
try {
process(things.get(i));
}
catch (Exception e) {
throw new BatchListenerFailedException("Failed to process", i);
}
}
}
When the container is configured with AckMode.MANUAL_IMMEDIATE, the error handler can be configured to commit the offset of recovered records; set the commitRecovered property to true.
See also Publishing Dead-letter Records.
When using transactions, similar functionality is provided by the DefaultAfterRollbackProcessor.
See After-rollback Processor.
The DefaultErrorHandler considers certain exceptions to be fatal, and retries are skipped for such exceptions; the recoverer is invoked on the first failure.
The exceptions that are considered fatal, by default, are:
-
DeserializationException -
MessageConversionException -
ConversionException -
MethodArgumentResolutionException -
NoSuchMethodException -
ClassCastException
since these exceptions are unlikely to be resolved on a retried delivery.
You can add more exception types to the not-retryable category, or completely replace the map of classified exceptions.
See the Javadocs for DefaultErrorHandler.addNotRetryableException() and DefaultErrorHandler.setClassifications() for more information, as well as those for the spring-retry BinaryExceptionClassifier.
Here is an example that adds IllegalArgumentException to the not-retryable exceptions:
@Bean
public DefaultErrorHandler errorHandler(ConsumerRecordRecoverer recoverer) {
DefaultErrorHandler handler = new DefaultErrorHandler(recoverer);
handler.addNotRetryableExceptions(IllegalArgumentException.class);
return handler;
}
The error handler can be configured with one or more RetryListener s, receiving notifications of retry and recovery progress.
Starting with version 2.8.10, methods for batch listeners were added.
@FunctionalInterface
public interface RetryListener {
void failedDelivery(ConsumerRecord<?, ?> record, Exception ex, int deliveryAttempt);
default void recovered(ConsumerRecord<?, ?> record, Exception ex) {
}
default void recoveryFailed(ConsumerRecord<?, ?> record, Exception original, Exception failure) {
}
default void failedDelivery(ConsumerRecords<?, ?> records, Exception ex, int deliveryAttempt) {
}
default void recovered(ConsumerRecords<?, ?> records, Exception ex) {
}
default void recoveryFailed(ConsumerRecords<?, ?> records, Exception original, Exception failure) {
}
}
See the javadocs for more information.
If the recoverer fails (throws an exception), the failed record will be included in the seeks.
If the recoverer fails, the BackOff will be reset by default and redeliveries will again go through the back offs before recovery is attempted again.
To skip retries after a recovery failure, set the error handler’s resetStateOnRecoveryFailure to false.
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You can provide the error handler with a BiFunction<ConsumerRecord<?, ?>, Exception, BackOff> to determine the BackOff to use, based on the failed record and/or the exception:
handler.setBackOffFunction((record, ex) -> { ... });
If the function returns null, the handler’s default BackOff will be used.
Set resetStateOnExceptionChange to true and the retry sequence will be restarted (including the selection of a new BackOff, if so configured) if the exception type changes between failures.
When false (the default before version 2.9), the exception type is not considered.
Starting with version 2.9, this is now true by default.
Also see Delivery Attempts Header.
Conversion Errors with Batch Error Handlers
Starting with version 2.8, batch listeners can now properly handle conversion errors, when using a MessageConverter with a ByteArrayDeserializer, a BytesDeserializer or a StringDeserializer, as well as a DefaultErrorHandler.
When a conversion error occurs, the payload is set to null and a deserialization exception is added to the record headers, similar to the ErrorHandlingDeserializer.
A list of ConversionException s is available in the listener so the listener can throw a BatchListenerFailedException indicating the first index at which a conversion exception occurred.
Example:
@KafkaListener(id = "test", topics = "topic")
void listen(List<Thing> in, @Header(KafkaHeaders.CONVERSION_FAILURES) List<ConversionException> exceptions) {
for (int i = 0; i < in.size(); i++) {
Foo foo = in.get(i);
if (foo == null && exceptions.get(i) != null) {
throw new BatchListenerFailedException("Conversion error", exceptions.get(i), i);
}
process(foo);
}
}
Retrying Complete Batches
This is now the fallback behavior of the DefaultErrorHandler for a batch listener where the listener throws an exception other than a BatchListenerFailedException.
There is no guarantee that, when a batch is redelivered, the batch has the same number of records and/or the redelivered records are in the same order.
It is impossible, therefore, to easily maintain retry state for a batch.
The FallbackBatchErrorHandler takes a the following approach.
If a batch listener throws an exception that is not a BatchListenerFailedException, the retries are performed from the in-memory batch of records.
In order to avoid a rebalance during an extended retry sequence, the error handler pauses the consumer, polls it before sleeping for the back off, for each retry, and calls the listener again.
If/when retries are exhausted, the ConsumerRecordRecoverer is called for each record in the batch.
If the recoverer throws an exception, or the thread is interrupted during its sleep, the batch of records will be redelivered on the next poll.
Before exiting, regardless of the outcome, the consumer is resumed.
| This mechanism cannot be used with transactions. |
While waiting for a BackOff interval, the error handler will loop with a short sleep until the desired delay is reached, while checking to see if the container has been stopped, allowing the sleep to exit soon after the stop() rather than causing a delay.
Container Stopping Error Handlers
The CommonContainerStoppingErrorHandler stops the container if the listener throws an exception.
For record listeners, when the AckMode is RECORD, offsets for already processed records are committed.
For record listeners, when the AckMode is any manual value, offsets for already acknowledged records are committed.
For record listeners, wWhen the AckMode is BATCH, or for batch listeners, the entire batch is replayed when the container is restarted.
After the container stops, an exception that wraps the ListenerExecutionFailedException is thrown.
This is to cause the transaction to roll back (if transactions are enabled).
Delegating Error Handler
The CommonDelegatingErrorHandler can delegate to different error handlers, depending on the exception type.
For example, you may wish to invoke a DefaultErrorHandler for most exceptions, or a CommonContainerStoppingErrorHandler for others.
Logging Error Handler
The CommonLoggingErrorHandler simply logs the exception; with a record listener, the remaining records from the previous poll are passed to the listener.
For a batch listener, all the records in the batch are logged.
Using Different Common Error Handlers for Record and Batch Listeners
If you wish to use a different error handling strategy for record and batch listeners, the CommonMixedErrorHandler is provided allowing the configuration of a specific error handler for each listener type.
Common Error Handler Summary
-
DefaultErrorHandler -
CommonContainerStoppingErrorHandler -
CommonDelegatingErrorHandler -
CommonLoggingErrorHandler -
CommonMixedErrorHandler
Legacy Error Handlers and Their Replacements
| Legacy Error Handler | Replacement |
|---|---|
|
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|
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No replacement, use |
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No replacements - use |
Migrating Custom Legacy Error Handler Implementations to CommonErrorHandler
Refer to the javadocs in CommonErrorHandler.
To replace an ErrorHandler or ConsumerAwareErrorHandler implementation, you should implement handleOne() and leave seeksAfterHandle() to return false (default).
You should also implement handleOtherException() - to handle exceptions that occur outside the scope of record processing (e.g. consumer errors).
To replace a RemainingRecordsErrorHandler implementation, you should implement handleRemaining() and override seeksAfterHandle() to return true (the error handler must perform the necessary seeks).
You should also implement handleOtherException() - to handle exceptions that occur outside the scope of record processing (e.g. consumer errors).
To replace any BatchErrorHandler implementation, you should implement handleBatch()
You should also implement handleOtherException() - to handle exceptions that occur outside the scope of record processing (e.g. consumer errors).
After-rollback Processor
When using transactions, if the listener throws an exception (and an error handler, if present, throws an exception), the transaction is rolled back.
By default, any unprocessed records (including the failed record) are re-fetched on the next poll.
This is achieved by performing seek operations in the DefaultAfterRollbackProcessor.
With a batch listener, the entire batch of records is reprocessed (the container has no knowledge of which record in the batch failed).
To modify this behavior, you can configure the listener container with a custom AfterRollbackProcessor.
For example, with a record-based listener, you might want to keep track of the failed record and give up after some number of attempts, perhaps by publishing it to a dead-letter topic.
Starting with version 2.2, the DefaultAfterRollbackProcessor can now recover (skip) a record that keeps failing.
By default, after ten failures, the failed record is logged (at the ERROR level).
You can configure the processor with a custom recoverer (BiConsumer) and maximum failures.
Setting the maxFailures property to a negative number causes infinite retries.
The following example configures recovery after three tries:
AfterRollbackProcessor<String, String> processor =
new DefaultAfterRollbackProcessor((record, exception) -> {
// recover after 3 failures, with no back off - e.g. send to a dead-letter topic
}, new FixedBackOff(0L, 2L));
When you do not use transactions, you can achieve similar functionality by configuring a DefaultErrorHandler.
See Container Error Handlers.
| Recovery is not possible with a batch listener, since the framework has no knowledge about which record in the batch keeps failing. In such cases, the application listener must handle a record that keeps failing. |
See also Publishing Dead-letter Records.
Starting with version 2.2.5, the DefaultAfterRollbackProcessor can be invoked in a new transaction (started after the failed transaction rolls back).
Then, if you are using the DeadLetterPublishingRecoverer to publish a failed record, the processor will send the recovered record’s offset in the original topic/partition to the transaction.
To enable this feature, set the commitRecovered and kafkaTemplate properties on the DefaultAfterRollbackProcessor.
If the recoverer fails (throws an exception), the failed record will be included in the seeks.
Starting with version 2.5.5, if the recoverer fails, the BackOff will be reset by default and redeliveries will again go through the back offs before recovery is attempted again.
With earlier versions, the BackOff was not reset and recovery was re-attempted on the next failure.
To revert to the previous behavior, set the processor’s resetStateOnRecoveryFailure property to false.
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Starting with version 2.6, you can now provide the processor with a BiFunction<ConsumerRecord<?, ?>, Exception, BackOff> to determine the BackOff to use, based on the failed record and/or the exception:
handler.setBackOffFunction((record, ex) -> { ... });
If the function returns null, the processor’s default BackOff will be used.
Starting with version 2.6.3, set resetStateOnExceptionChange to true and the retry sequence will be restarted (including the selection of a new BackOff, if so configured) if the exception type changes between failures.
By default, the exception type is not considered.
Starting with version 2.3.1, similar to the DefaultErrorHandler, the DefaultAfterRollbackProcessor considers certain exceptions to be fatal, and retries are skipped for such exceptions; the recoverer is invoked on the first failure.
The exceptions that are considered fatal, by default, are:
-
DeserializationException -
MessageConversionException -
ConversionException -
MethodArgumentResolutionException -
NoSuchMethodException -
ClassCastException
since these exceptions are unlikely to be resolved on a retried delivery.
You can add more exception types to the not-retryable category, or completely replace the map of classified exceptions.
See the Javadocs for DefaultAfterRollbackProcessor.setClassifications() for more information, as well as those for the spring-retry BinaryExceptionClassifier.
Here is an example that adds IllegalArgumentException to the not-retryable exceptions:
@Bean
public DefaultAfterRollbackProcessor errorHandler(BiConsumer<ConsumerRecord<?, ?>, Exception> recoverer) {
DefaultAfterRollbackProcessor processor = new DefaultAfterRollbackProcessor(recoverer);
processor.addNotRetryableException(IllegalArgumentException.class);
return processor;
}
Also see Delivery Attempts Header.
With current kafka-clients, the container cannot detect whether a ProducerFencedException is caused by a rebalance or if the producer’s transactional.id has been revoked due to a timeout or expiry.
Because, in most cases, it is caused by a rebalance, the container does not call the AfterRollbackProcessor (because it’s not appropriate to seek the partitions because we no longer are assigned them).
If you ensure the timeout is large enough to process each transaction and periodically perform an "empty" transaction (e.g. via a ListenerContainerIdleEvent) you can avoid fencing due to timeout and expiry.
Or, you can set the stopContainerWhenFenced container property to true and the container will stop, avoiding the loss of records.
You can consume a ConsumerStoppedEvent and check the Reason property for FENCED to detect this condition.
Since the event also has a reference to the container, you can restart the container using this event.
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Starting with version 2.7, while waiting for a BackOff interval, the error handler will loop with a short sleep until the desired delay is reached, while checking to see if the container has been stopped, allowing the sleep to exit soon after the stop() rather than causing a delay.
Starting with version 2.7, the processor can be configured with one or more RetryListener s, receiving notifications of retry and recovery progress.
@FunctionalInterface
public interface RetryListener {
void failedDelivery(ConsumerRecord<?, ?> record, Exception ex, int deliveryAttempt);
default void recovered(ConsumerRecord<?, ?> record, Exception ex) {
}
default void recoveryFailed(ConsumerRecord<?, ?> record, Exception original, Exception failure) {
}
}
See the javadocs for more information.
Delivery Attempts Header
The following applies to record listeners only, not batch listeners.
Starting with version 2.5, when using an ErrorHandler or AfterRollbackProcessor that implements DeliveryAttemptAware, it is possible to enable the addition of the KafkaHeaders.DELIVERY_ATTEMPT header (kafka_deliveryAttempt) to the record.
The value of this header is an incrementing integer starting at 1.
When receiving a raw ConsumerRecord<?, ?> the integer is in a byte[4].
int delivery = ByteBuffer.wrap(record.headers()
.lastHeader(KafkaHeaders.DELIVERY_ATTEMPT).value())
.getInt()
When using @KafkaListener with the DefaultKafkaHeaderMapper or SimpleKafkaHeaderMapper, it can be obtained by adding @Header(KafkaHeaders.DELIVERY_ATTEMPT) int delivery as a parameter to the listener method.
To enable population of this header, set the container property deliveryAttemptHeader to true.
It is disabled by default to avoid the (small) overhead of looking up the state for each record and adding the header.
The DefaultErrorHandler and DefaultAfterRollbackProcessor support this feature.
Listener Info Header
In some cases, it is useful to be able to know which container a listener is running in.
Starting with version 2.8.4, you can now set the listenerInfo property on the listener container, or set the info attribute on the @KafkaListener annotation.
Then, the container will add this in the KafkaListener.LISTENER_INFO header to all incoming messages; it can then be used in record interceptors, filters, etc., or in the listener itself.
@KafkaListener(id = "something", topic = "topic", filter = "someFilter",
info = "this is the something listener")
public void listen2(@Payload Thing thing,
@Header(KafkaHeaders.LISTENER_INFO) String listenerInfo) {
...
}
When used in a RecordInterceptor or RecordFilterStrategy implementation, the header is in the consumer record as a byte array, converted using the KafkaListenerAnnotationBeanPostProcessor 's charSet property.
The header mappers also convert to String when creating MessageHeaders from the consumer record and never map this header on an outbound record.
For POJO batch listeners, starting with version 2.8.6, the header is copied into each member of the batch and is also available as a single String parameter after conversion.
@KafkaListener(id = "list2", topics = "someTopic", containerFactory = "batchFactory",
info = "info for batch")
public void listen(List<Thing> list,
@Header(KafkaHeaders.RECEIVED_KEY) List<Integer> keys,
@Header(KafkaHeaders.RECEIVED_PARTITION) List<Integer> partitions,
@Header(KafkaHeaders.RECEIVED_TOPIC) List<String> topics,
@Header(KafkaHeaders.OFFSET) List<Long> offsets,
@Header(KafkaHeaders.LISTENER_INFO) String info) {
...
}
If the batch listener has a filter and the filter results in an empty batch, you will need to add required = false to the @Header parameter because the info is not available for an empty batch.
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If you receive List<Message<Thing>> the info is in the KafkaHeaders.LISTENER_INFO header of each Message<?>.
See Batch Listeners for more information about consuming batches.
Publishing Dead-letter Records
You can configure the DefaultErrorHandler and DefaultAfterRollbackProcessor with a record recoverer when the maximum number of failures is reached for a record.
The framework provides the DeadLetterPublishingRecoverer, which publishes the failed message to another topic.
The recoverer requires a KafkaTemplate<Object, Object>, which is used to send the record.
You can also, optionally, configure it with a BiFunction<ConsumerRecord<?, ?>, Exception, TopicPartition>, which is called to resolve the destination topic and partition.
By default, the dead-letter record is sent to a topic named <originalTopic>.DLT (the original topic name suffixed with .DLT) and to the same partition as the original record.
Therefore, when you use the default resolver, the dead-letter topic must have at least as many partitions as the original topic.
|
If the returned TopicPartition has a negative partition, the partition is not set in the ProducerRecord, so the partition is selected by Kafka.
Starting with version 2.2.4, any ListenerExecutionFailedException (thrown, for example, when an exception is detected in a @KafkaListener method) is enhanced with the groupId property.
This allows the destination resolver to use this, in addition to the information in the ConsumerRecord to select the dead letter topic.
The following example shows how to wire a custom destination resolver:
DeadLetterPublishingRecoverer recoverer = new DeadLetterPublishingRecoverer(template,
(r, e) -> {
if (e instanceof FooException) {
return new TopicPartition(r.topic() + ".Foo.failures", r.partition());
}
else {
return new TopicPartition(r.topic() + ".other.failures", r.partition());
}
});
CommonErrorHandler errorHandler = new DefaultErrorHandler(recoverer, new FixedBackOff(0L, 2L));
The record sent to the dead-letter topic is enhanced with the following headers:
-
KafkaHeaders.DLT_EXCEPTION_FQCN: The Exception class name (generally aListenerExecutionFailedException, but can be others). -
KafkaHeaders.DLT_EXCEPTION_CAUSE_FQCN: The Exception cause class name, if present (since version 2.8). -
KafkaHeaders.DLT_EXCEPTION_STACKTRACE: The Exception stack trace. -
KafkaHeaders.DLT_EXCEPTION_MESSAGE: The Exception message. -
KafkaHeaders.DLT_KEY_EXCEPTION_FQCN: The Exception class name (key deserialization errors only). -
KafkaHeaders.DLT_KEY_EXCEPTION_STACKTRACE: The Exception stack trace (key deserialization errors only). -
KafkaHeaders.DLT_KEY_EXCEPTION_MESSAGE: The Exception message (key deserialization errors only). -
KafkaHeaders.DLT_ORIGINAL_TOPIC: The original topic. -
KafkaHeaders.DLT_ORIGINAL_PARTITION: The original partition. -
KafkaHeaders.DLT_ORIGINAL_OFFSET: The original offset. -
KafkaHeaders.DLT_ORIGINAL_TIMESTAMP: The original timestamp. -
KafkaHeaders.DLT_ORIGINAL_TIMESTAMP_TYPE: The original timestamp type. -
KafkaHeaders.DLT_ORIGINAL_CONSUMER_GROUP: The original consumer group that failed to process the record (since version 2.8).
Key exceptions are only caused by DeserializationException s so there is no DLT_KEY_EXCEPTION_CAUSE_FQCN.
There are two mechanisms to add more headers.
-
Subclass the recoverer and override
createProducerRecord()- callsuper.createProducerRecord()and add more headers. -
Provide a
BiFunctionto receive the consumer record and exception, returning aHeadersobject; headers from there will be copied to the final producer record; also see Managing Dead Letter Record Headers. UsesetHeadersFunction()to set theBiFunction.
The second is simpler to implement but the first has more information available, including the already assembled standard headers.
Starting with version 2.3, when used in conjunction with an ErrorHandlingDeserializer, the publisher will restore the record value(), in the dead-letter producer record, to the original value that failed to be deserialized.
Previously, the value() was null and user code had to decode the DeserializationException from the message headers.
In addition, you can provide multiple KafkaTemplate s to the publisher; this might be needed, for example, if you want to publish the byte[] from a DeserializationException, as well as values using a different serializer from records that were deserialized successfully.
Here is an example of configuring the publisher with KafkaTemplate s that use a String and byte[] serializer:
@Bean
public DeadLetterPublishingRecoverer publisher(KafkaTemplate<?, ?> stringTemplate,
KafkaTemplate<?, ?> bytesTemplate) {
Map<Class<?>, KafkaTemplate<?, ?>> templates = new LinkedHashMap<>();
templates.put(String.class, stringTemplate);
templates.put(byte[].class, bytesTemplate);
return new DeadLetterPublishingRecoverer(templates);
}
The publisher uses the map keys to locate a template that is suitable for the value() about to be published.
A LinkedHashMap is recommended so that the keys are examined in order.
When publishing null values, when there are multiple templates, the recoverer will look for a template for the Void class; if none is present, the first template from the values().iterator() will be used.
Since 2.7 you can use the setFailIfSendResultIsError method so that an exception is thrown when message publishing fails.
You can also set a timeout for the verification of the sender success with setWaitForSendResultTimeout.
If the recoverer fails (throws an exception), the failed record will be included in the seeks.
Starting with version 2.5.5, if the recoverer fails, the BackOff will be reset by default and redeliveries will again go through the back offs before recovery is attempted again.
With earlier versions, the BackOff was not reset and recovery was re-attempted on the next failure.
To revert to the previous behavior, set the error handler’s resetStateOnRecoveryFailure property to false.
|
Starting with version 2.6.3, set resetStateOnExceptionChange to true and the retry sequence will be restarted (including the selection of a new BackOff, if so configured) if the exception type changes between failures.
By default, the exception type is not considered.
Starting with version 2.3, the recoverer can also be used with Kafka Streams - see Recovery from Deserialization Exceptions for more information.
The ErrorHandlingDeserializer adds the deserialization exception(s) in headers ErrorHandlingDeserializer.VALUE_DESERIALIZER_EXCEPTION_HEADER and ErrorHandlingDeserializer.KEY_DESERIALIZER_EXCEPTION_HEADER (using java serialization).
By default, these headers are not retained in the message published to the dead letter topic.
Starting with version 2.7, if both the key and value fail deserialization, the original values of both are populated in the record sent to the DLT.
If incoming records are dependent on each other, but may arrive out of order, it may be useful to republish a failed record to the tail of the original topic (for some number of times), instead of sending it directly to the dead letter topic. See this Stack Overflow Question for an example.
The following error handler configuration will do exactly that:
@Bean
public ErrorHandler eh(KafkaOperations<String, String> template) {
return new DefaultErrorHandler(new DeadLetterPublishingRecoverer(template,
(rec, ex) -> {
org.apache.kafka.common.header.Header retries = rec.headers().lastHeader("retries");
if (retries == null) {
retries = new RecordHeader("retries", new byte[] { 1 });
rec.headers().add(retries);
}
else {
retries.value()[0]++;
}
return retries.value()[0] > 5
? new TopicPartition("topic.DLT", rec.partition())
: new TopicPartition("topic", rec.partition());
}), new FixedBackOff(0L, 0L));
}
Starting with version 2.7, the recoverer checks that the partition selected by the destination resolver actually exists.
If the partition is not present, the partition in the ProducerRecord is set to null, allowing the KafkaProducer to select the partition.
You can disable this check by setting the verifyPartition property to false.
Managing Dead Letter Record Headers
Referring to Publishing Dead-letter Records above, the DeadLetterPublishingRecoverer has two properties used to manage headers when those headers already exist (such as when reprocessing a dead letter record that failed, including when using Non-Blocking Retries).
-
appendOriginalHeaders(defaulttrue) -
stripPreviousExceptionHeaders(defaulttruesince version 2.8)
Apache Kafka supports multiple headers with the same name; to obtain the "latest" value, you can use headers.lastHeader(headerName); to get an iterator over multiple headers, use headers.headers(headerName).iterator().
When repeatedly republishing a failed record, these headers can grow (and eventually cause publication to fail due to a RecordTooLargeException); this is especially true for the exception headers and particularly for the stack trace headers.
The reason for the two properties is because, while you might want to retain only the last exception information, you might want to retain the history of which topic(s) the record passed through for each failure.
appendOriginalHeaders is applied to all headers named ORIGINAL while stripPreviousExceptionHeaders is applied to all headers named EXCEPTION.
Starting with version 2.8.4, you now can control which of the standard headers will be added to the output record.
See the enum HeadersToAdd for the generic names of the (currently) 10 standard headers that are added by default (these are not the actual header names, just an abstraction; the actual header names are set up by the getHeaderNames() method which subclasses can override.
To exclude headers, use the excludeHeaders() method; for example, to suppress adding the exception stack trace in a header, use:
DeadLetterPublishingRecoverer recoverer = new DeadLetterPublishingRecoverer(template);
recoverer.excludeHeaders(HeaderNames.HeadersToAdd.EX_STACKTRACE);
In addition, you can completely customize the addition of exception headers by adding an ExceptionHeadersCreator; this also disables all standard exception headers.
DeadLetterPublishingRecoverer recoverer = new DeadLetterPublishingRecoverer(template);
recoverer.setExceptionHeadersCreator((kafkaHeaders, exception, isKey, headerNames) -> {
kafkaHeaders.add(new RecordHeader(..., ...));
});
Also starting with version 2.8.4, you can now provide multiple headers functions, via the addHeadersFunction method.
This allows additional functions to apply, even if another function has already been registered, for example, when using Non-Blocking Retries.
Also see Failure Header Management with Non-Blocking Retries.
ExponentialBackOffWithMaxRetries Implementation
Spring Framework provides a number of BackOff implementations.
By default, the ExponentialBackOff will retry indefinitely; to give up after some number of retry attempts requires calculating the maxElapsedTime.
Since version 2.7.3, Spring for Apache Kafka provides the ExponentialBackOffWithMaxRetries which is a subclass that receives the maxRetries property and automatically calculates the maxElapsedTime, which is a little more convenient.
@Bean
DefaultErrorHandler handler() {
ExponentialBackOffWithMaxRetries bo = new ExponentialBackOffWithMaxRetries(6);
bo.setInitialInterval(1_000L);
bo.setMultiplier(2.0);
bo.setMaxInterval(10_000L);
return new DefaultErrorHandler(myRecoverer, bo);
}
This will retry after 1, 2, 4, 8, 10, 10 seconds, before calling the recoverer.
4.1.23. JAAS and Kerberos
Starting with version 2.0, a KafkaJaasLoginModuleInitializer class has been added to assist with Kerberos configuration.
You can add this bean, with the desired configuration, to your application context.
The following example configures such a bean:
@Bean
public KafkaJaasLoginModuleInitializer jaasConfig() throws IOException {
KafkaJaasLoginModuleInitializer jaasConfig = new KafkaJaasLoginModuleInitializer();
jaasConfig.setControlFlag("REQUIRED");
Map<String, String> options = new HashMap<>();
options.put("useKeyTab", "true");
options.put("storeKey", "true");
options.put("keyTab", "/etc/security/keytabs/kafka_client.keytab");
options.put("principal", "[email protected]");
jaasConfig.setOptions(options);
return jaasConfig;
}
4.2. Non-Blocking Retries
Version 2.9 changed the mechanism to bootstrap infrastructure beans; see Configuration for the two mechanisms that are now required to bootstrap the feature.
Achieving non-blocking retry / dlt functionality with Kafka usually requires setting up extra topics and creating and configuring the corresponding listeners.
Since 2.7 Spring for Apache Kafka offers support for that via the @RetryableTopic annotation and RetryTopicConfiguration class to simplify that bootstrapping.
| Non-blocking retries are not supported with Batch Listeners. |
4.2.1. How The Pattern Works
If message processing fails, the message is forwarded to a retry topic with a back off timestamp. The retry topic consumer then checks the timestamp and if it’s not due it pauses the consumption for that topic’s partition. When it is due the partition consumption is resumed, and the message is consumed again. If the message processing fails again the message will be forwarded to the next retry topic, and the pattern is repeated until a successful processing occurs, or the attempts are exhausted, and the message is sent to the Dead Letter Topic (if configured).
To illustrate, if you have a "main-topic" topic, and want to setup non-blocking retry with an exponential backoff of 1000ms with a multiplier of 2 and 4 max attempts, it will create the main-topic-retry-1000, main-topic-retry-2000, main-topic-retry-4000 and main-topic-dlt topics and configure the respective consumers. The framework also takes care of creating the topics and setting up and configuring the listeners.
| By using this strategy you lose Kafka’s ordering guarantees for that topic. |
You can set the AckMode mode you prefer, but RECORD is suggested.
|
At this time this functionality doesn’t support class level @KafkaListener annotations
|
When using a manual AckMode with asyncAcks set to true, the DefaultErrorHandler must be configured with seekAfterError set to false.
Starting with versions 2.9.10, 3.0.8, this will be set to true unconditionally for such configurations.
With earlier versions, it was necessary to override the RetryConfigurationSupport.configureCustomizers() method to set the property to true.
@Override
protected void configureCustomizers(CustomizersConfigurer customizersConfigurer) {
customizersConfigurer.customizeErrorHandler(eh -> eh.setSeekAfterError(false));
}
In addition, before those versions, using the default (logging) DLT handler was not compatible with any kind of manual AckMode, regardless of the asyncAcks property.
4.2.2. Back Off Delay Precision
Overview and Guarantees
All message processing and backing off is handled by the consumer thread, and, as such, delay precision is guaranteed on a best-effort basis. If one message’s processing takes longer than the next message’s back off period for that consumer, the next message’s delay will be higher than expected. Also, for short delays (about 1s or less), the maintenance work the thread has to do, such as committing offsets, may delay the message processing execution. The precision can also be affected if the retry topic’s consumer is handling more than one partition, because we rely on waking up the consumer from polling and having full pollTimeouts to make timing adjustments.
That being said, for consumers handling a single partition the message’s processing should occur approximately at its exact due time for most situations.
| It is guaranteed that a message will never be processed before its due time. |
4.2.3. Configuration
Starting with version 2.9, for default configuration, the @EnableKafkaRetryTopic annotation should be used in a @Configuration annotated class.
This enables the feature to bootstrap properly and gives access to injecting some of the feature’s components to be looked up at runtime.
It is not necessary to also add @EnableKafka, if you add this annotation, because @EnableKafkaRetryTopic is meta-annotated with @EnableKafka.
|
Also, starting with that version, for more advanced configuration of the feature’s components and global features, the RetryTopicConfigurationSupport class should be extended in a @Configuration class, and the appropriate methods overridden.
For more details refer to Configuring Global Settings and Features.
By default, the containers for the retry topics will have the same concurrency as the main container.
Starting with version 3.0, you can set a different concurrency for the retry containers (either on the annotation, or in RetryConfigurationBuilder).
Only one of the above techniques can be used, and only one @Configuration class can extend RetryTopicConfigurationSupport.
|
Using the @RetryableTopic annotation
To configure the retry topic and dlt for a @KafkaListener annotated method, you just have to add the @RetryableTopic annotation to it and Spring for Apache Kafka will bootstrap all the necessary topics and consumers with the default configurations.
@RetryableTopic(kafkaTemplate = "myRetryableTopicKafkaTemplate")
@KafkaListener(topics = "my-annotated-topic", groupId = "myGroupId")
public void processMessage(MyPojo message) {
// ... message processing
}
You can specify a method in the same class to process the dlt messages by annotating it with the @DltHandler annotation.
If no DltHandler method is provided a default consumer is created which only logs the consumption.
@DltHandler
public void processMessage(MyPojo message) {
// ... message processing, persistence, etc
}
If you don’t specify a kafkaTemplate name a bean with name defaultRetryTopicKafkaTemplate will be looked up.
If no bean is found an exception is thrown.
|
Starting with version 3.0, the @RetryableTopic annotation can be used as a meta-annotation on custom annotations; for example:
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@RetryableTopic
static @interface MetaAnnotatedRetryableTopic {
@AliasFor(attribute = "concurrency", annotation = RetryableTopic.class)
String parallelism() default "3";
}
Using RetryTopicConfiguration beans
You can also configure the non-blocking retry support by creating RetryTopicConfiguration beans in a @Configuration annotated class.
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, Object> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.create(template);
}
This will create retry topics and a dlt, as well as the corresponding consumers, for all topics in methods annotated with '@KafkaListener' using the default configurations. The KafkaTemplate instance is required for message forwarding.
To achieve more fine-grained control over how to handle non-blocking retrials for each topic, more than one RetryTopicConfiguration bean can be provided.
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.fixedBackOff(3000)
.maxAttempts(5)
.concurrency(1)
.includeTopics("my-topic", "my-other-topic")
.create(template);
}
@Bean
public RetryTopicConfiguration myOtherRetryTopic(KafkaTemplate<String, MyOtherPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.exponentialBackoff(1000, 2, 5000)
.maxAttempts(4)
.excludeTopics("my-topic", "my-other-topic")
.retryOn(MyException.class)
.create(template);
}
The retry topics' and dlt’s consumers will be assigned to a consumer group with a group id that is the combination of the one with you provide in the groupId parameter of the @KafkaListener annotation with the topic’s suffix.
If you don’t provide any they’ll all belong to the same group, and rebalance on a retry topic will cause an unnecessary rebalance on the main topic.
|
If the consumer is configured with an ErrorHandlingDeserializer, to handle deserilialization exceptions, it is important to configure the KafkaTemplate and its producer with a serializer that can handle normal objects as well as raw byte[] values, which result from deserialization exceptions.
The generic value type of the template should be Object.
One technique is to use the DelegatingByTypeSerializer; an example follows:
|
@Bean
public ProducerFactory<String, Object> producerFactory() {
return new DefaultKafkaProducerFactory<>(producerConfiguration(), new StringSerializer(),
new DelegatingByTypeSerializer(Map.of(byte[].class, new ByteArraySerializer(),
MyNormalObject.class, new JsonSerializer<Object>())));
}
@Bean
public KafkaTemplate<String, Object> kafkaTemplate() {
return new KafkaTemplate<>(producerFactory());
}
Multiple @KafkaListener annotations can be used for the same topic with or without manual partition assignment along with non-blocking retries, but only one configuration will be used for a given topic.
It’s best to use a single RetryTopicConfiguration bean for configuration of such topics; if multiple @RetryableTopic annotations are being used for the same topic, all of them should have the same values, otherwise one of them will be applied to all of that topic’s listeners and the other annotations' values will be ignored.
|
Configuring Global Settings and Features
Since 2.9, the previous bean overriding approach for configuring components has been removed (without deprecation, due to the aforementioned experimental nature of the API).
This does not change the RetryTopicConfiguration beans approach - only infrastructure components' configurations.
Now the RetryTopicConfigurationSupport class should be extended in a (single) @Configuration class, and the proper methods overridden.
An example follows:
@EnableKafka
@Configuration
public class MyRetryTopicConfiguration extends RetryTopicConfigurationSupport {
@Override
protected void configureBlockingRetries(BlockingRetriesConfigurer blockingRetries) {
blockingRetries
.retryOn(MyBlockingRetriesException.class, MyOtherBlockingRetriesException.class)
.backOff(new FixedBackOff(3000, 3));
}
@Override
protected void manageNonBlockingFatalExceptions(List<Class<? extends Throwable>> nonBlockingFatalExceptions) {
nonBlockingFatalExceptions.add(MyNonBlockingException.class);
}
@Override
protected void configureCustomizers(CustomizersConfigurer customizersConfigurer) {
// Use the new 2.9 mechanism to avoid re-fetching the same records after a pause
customizersConfigurer.customizeErrorHandler(eh -> {
eh.setSeekAfterError(false);
});
}
}
When using this configuration approach, the @EnableKafkaRetryTopic annotation should not be used to prevent context failing to start due to duplicated beans.
Use the simple @EnableKafka annotation instead.
|
When autoCreateTopics is true, the main and retry topics will be created with the specified number of partitions and replication factor.
Starting with version 3.0, the default replication factor is -1, meaning use the broker default.
If your broker version is earlier than 2.4, you will need to set an explicit value.
To override these values for a particular topic (e.g. the main topic or DLT), simply add a NewTopic @Bean with the required properties; that will override the auto creation properties.
| By default, records are published to the retry topic(s) using the original partition of the received record. If the retry topics have fewer partitions than the main topic, you should configure the framework appropriately; an example follows. |
@EnableKafka
@Configuration
public class Config extends RetryTopicConfigurationSupport {
@Override
protected Consumer<DeadLetterPublishingRecovererFactory> configureDeadLetterPublishingContainerFactory() {
return dlprf -> dlprf.setPartitionResolver((cr, nextTopic) -> null);
}
...
}
The parameters to the function are the consumer record and the name of the next topic.
You can return a specific partition number, or null to indicate that the KafkaProducer should determine the partition.
By default, all values of retry headers (number of attempts, timestamps) are retained when a record transitions through the retry topics.
Starting with version 2.9.6, if you want to retain just the last value of these headers, use the configureDeadLetterPublishingContainerFactory() method shown above to set the factory’s retainAllRetryHeaderValues property to false.
4.2.4. Programmatic Construction
The feature is designed to be used with @KafkaListener; however, several users have requested information on how to configure non-blocking retries programmatically.
The following Spring Boot application provides an example of how to do so.
@SpringBootApplication
public class Application extends RetryTopicConfigurationSupport {
public static void main(String[] args) {
SpringApplication.run(2Application.class, args);
}
@Bean
RetryTopicConfiguration retryConfig(KafkaTemplate<String, String> template) {
return RetryTopicConfigurationBuilder.newInstance()
.maxAttempts(4)
.autoCreateTopicsWith(2, (short) 1)
.create(template);
}
@Bean
TaskScheduler scheduler() {
return new ThreadPoolTaskScheduler();
}
@Bean
@Order(0)
SmartInitializingSingleton dynamicRetry(RetryTopicConfigurer configurer, RetryTopicConfiguration config,
KafkaListenerAnnotationBeanPostProcessor<?, ?> bpp, KafkaListenerContainerFactory<?> factory,
Listener listener, KafkaListenerEndpointRegistry registry) {
return () -> {
KafkaListenerEndpointRegistrar registrar = bpp.getEndpointRegistrar();
MethodKafkaListenerEndpoint<String, String> mainEndpoint = new MethodKafkaListenerEndpoint<>();
EndpointProcessor endpointProcessor = endpoint -> {
// customize as needed (e.g. apply attributes to retry endpoints).
if (!endpoint.equals(mainEndpoint)) {
endpoint.setConcurrency(1);
}
// these are required
endpoint.setMessageHandlerMethodFactory(bpp.getMessageHandlerMethodFactory());
endpoint.setTopics("topic");
endpoint.setId("id");
endpoint.setGroupId("group");
};
mainEndpoint.setBean(listener);
try {
mainEndpoint.setMethod(Listener.class.getDeclaredMethod("onMessage", ConsumerRecord.class));
}
catch (NoSuchMethodException | SecurityException ex) {
throw new IllegalStateException(ex);
}
mainEndpoint.setConcurrency(2);
mainEndpoint.setTopics("topic");
mainEndpoint.setId("id");
mainEndpoint.setGroupId("group");
configurer.processMainAndRetryListeners(endpointProcessor, mainEndpoint, config, registrar, factory,
"kafkaListenerContainerFactory");
};
}
@Bean
ApplicationRunner runner(KafkaTemplate<String, String> template) {
return args -> {
template.send("topic", "test");
};
}
}
@Component
class Listener implements MessageListener<String, String> {
@Override
public void onMessage(ConsumerRecord<String, String> record) {
System.out.println(KafkaUtils.format(record));
throw new RuntimeException("test");
}
}
| Auto creation of topics will only occur if the configuration is processed before the application context is refreshed, as in the above example. To configure containers at runtime, the topics will need to be created using some other technique. |
4.2.5. Features
Most of the features are available both for the @RetryableTopic annotation and the RetryTopicConfiguration beans.
BackOff Configuration
The BackOff configuration relies on the BackOffPolicy interface from the Spring Retry project.
It includes:
-
Fixed Back Off
-
Exponential Back Off
-
Random Exponential Back Off
-
Uniform Random Back Off
-
No Back Off
-
Custom Back Off
@RetryableTopic(attempts = 5,
backoff = @Backoff(delay = 1000, multiplier = 2, maxDelay = 5000))
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.fixedBackoff(3000)
.maxAttempts(4)
.create(template);
}
You can also provide a custom implementation of Spring Retry’s SleepingBackOffPolicy interface:
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.customBackOff(new MyCustomBackOffPolicy())
.maxAttempts(5)
.create(template);
}
The default backoff policy is FixedBackOffPolicy with a maximum of 3 attempts and 1000ms intervals.
|
There is a 30-second default maximum delay for the ExponentialBackOffPolicy.
If your back off policy requires delays with values bigger than that, adjust the maxDelay property accordingly.
|
The first attempt counts against maxAttempts, so if you provide a maxAttempts value of 4 there’ll be the original attempt plus 3 retries.
|
Global timeout
You can set the global timeout for the retrying process. If that time is reached, the next time the consumer throws an exception the message goes straight to the DLT, or just ends the processing if no DLT is available.
@RetryableTopic(backoff = @Backoff(2000), timeout = 5000)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.fixedBackoff(2000)
.timeoutAfter(5000)
.create(template);
}
| The default is having no timeout set, which can also be achieved by providing -1 as the timout value. |
Exception Classifier
You can specify which exceptions you want to retry on and which not to. You can also set it to traverse the causes to lookup nested exceptions.
@RetryableTopic(include = {MyRetryException.class, MyOtherRetryException.class}, traversingCauses = true)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
throw new RuntimeException(new MyRetryException()); // Will retry
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyOtherPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.notRetryOn(MyDontRetryException.class)
.create(template);
}
| The default behavior is retrying on all exceptions and not traversing causes. |
Since 2.8.3 there’s a global list of fatal exceptions which will cause the record to be sent to the DLT without any retries.
See DefaultErrorHandler for the default list of fatal exceptions.
You can add or remove exceptions to and from this list by overriding the configureNonBlockingRetries method in a @Configuration class that extends RetryTopicConfigurationSupport.
See Configuring Global Settings and Features for more information.
@Override
protected void manageNonBlockingFatalExceptions(List<Class<? extends Throwable>> nonBlockingFatalExceptions) {
nonBlockingFatalExceptions.add(MyNonBlockingException.class);
}
| To disable fatal exceptions' classification, just clear the provided list. |
Include and Exclude Topics
You can decide which topics will and will not be handled by a RetryTopicConfiguration bean via the .includeTopic(String topic), .includeTopics(Collection<String> topics) .excludeTopic(String topic) and .excludeTopics(Collection<String> topics) methods.
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.includeTopics(List.of("my-included-topic", "my-other-included-topic"))
.create(template);
}
@Bean
public RetryTopicConfiguration myOtherRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.excludeTopic("my-excluded-topic")
.create(template);
}
| The default behavior is to include all topics. |
Topics AutoCreation
Unless otherwise specified the framework will auto create the required topics using NewTopic beans that are consumed by the KafkaAdmin bean.
You can specify the number of partitions and the replication factor with which the topics will be created, and you can turn this feature off.
Starting with version 3.0, the default replication factor is -1, meaning use the broker default.
If your broker version is earlier than 2.4, you will need to set an explicit value.
| Note that if you’re not using Spring Boot you’ll have to provide a KafkaAdmin bean in order to use this feature. |
@RetryableTopic(numPartitions = 2, replicationFactor = 3)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@RetryableTopic(autoCreateTopics = false)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.autoCreateTopicsWith(2, 3)
.create(template);
}
@Bean
public RetryTopicConfiguration myOtherRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.doNotAutoCreateRetryTopics()
.create(template);
}
| By default the topics are autocreated with one partition and a replication factor of -1 (meaning use the broker default). If your broker version is earlier than 2.4, you will need to set an explicit value. |
Failure Header Management
When considering how to manage failure headers (original headers and exception headers), the framework delegates to the DeadLetterPublishingRecover to decide whether to append or replace the headers.
By default, it explicitly sets appendOriginalHeaders to false and leaves stripPreviousExceptionHeaders to the default used by the DeadLetterPublishingRecover.
This means that only the first "original" and last exception headers are retained with the default configuration. This is to avoid creation of excessively large messages (due to the stack trace header, for example) when many retry steps are involved.
See Managing Dead Letter Record Headers for more information.
To reconfigure the framework to use different settings for these properties, configure a DeadLetterPublishingRecoverer customizer by overriding the configureCustomizers method in a @Configuration class that extends RetryTopicConfigurationSupport.
See Configuring Global Settings and Features for more details.
@Override
protected void configureCustomizers(CustomizersConfigurer customizersConfigurer) {
customizersConfigurer.customizeDeadLetterPublishingRecoverer(dlpr -> {
dlpr.setAppendOriginalHeaders(true);
dlpr.setStripPreviousExceptionHeaders(false);
});
}
Starting with version 2.8.4, if you wish to add custom headers (in addition to the retry information headers added by the factory, you can add a headersFunction to the factory - factory.setHeadersFunction((rec, ex) → { … })
By default, any headers added will be cumulative - Kafka headers can contain multiple values.
Starting with version 2.9.5, if the Headers returned by the function contains a header of type DeadLetterPublishingRecoverer.SingleRecordHeader, then any existing values for that header will be removed and only the new single value will remain.
Custom DeadLetterPublishingRecoverer
As can be seen in Failure Header Management it is possible to customize the default DeadLetterPublishingRecoverer instances created by the framework.
However, for some use cases, it is necessary to subclass the DeadLetterPublishingRecoverer, for example to override createProducerRecord() to modify the contents sent to the retry (or dead-letter) topics.
Starting with version 3.0.9, you can override the RetryConfigurationSupport.configureDeadLetterPublishingContainerFactory() method to provide a DeadLetterPublisherCreator instance, for example:
@Override
protected Consumer<DeadLetterPublishingRecovererFactory>
configureDeadLetterPublishingContainerFactory() {
return (factory) -> factory.setDeadLetterPublisherCreator(
(templateResolver, destinationResolver) ->
new CustomDLPR(templateResolver, destinationResolver));
}
It is recommended that you use the provided resolvers when constructing the custom instance.
4.2.6. Combining Blocking and Non-Blocking Retries
Starting in 2.8.4 you can configure the framework to use both blocking and non-blocking retries in conjunction.
For example, you can have a set of exceptions that would likely trigger errors on the next records as well, such as DatabaseAccessException, so you can retry the same record a few times before sending it to the retry topic, or straight to the DLT.
To configure blocking retries, override the configureBlockingRetries method in a @Configuration class that extends RetryTopicConfigurationSupport and add the exceptions you want to retry, along with the BackOff to be used.
The default BackOff is a FixedBackOff with no delay and 9 attempts.
See Configuring Global Settings and Features for more information.
@Override
protected void configureBlockingRetries(BlockingRetriesConfigurer blockingRetries) {
blockingRetries
.retryOn(MyBlockingRetryException.class, MyOtherBlockingRetryException.class)
.backOff(new FixedBackOff(3000, 5));
}
| In combination with the global retryable topic’s fatal exceptions classification, you can configure the framework for any behavior you’d like, such as having some exceptions trigger both blocking and non-blocking retries, trigger only one kind or the other, or go straight to the DLT without retries of any kind. |
Here’s an example with both configurations working together:
@Override
protected void configureBlockingRetries(BlockingRetriesConfigurer blockingRetries) {
blockingRetries
.retryOn(ShouldRetryOnlyBlockingException.class, ShouldRetryViaBothException.class)
.backOff(new FixedBackOff(50, 3));
}
@Override
protected void manageNonBlockingFatalExceptions(List<Class<? extends Throwable>> nonBlockingFatalExceptions) {
nonBlockingFatalExceptions.add(ShouldSkipBothRetriesException.class);
}
In this example:
-
ShouldRetryOnlyBlockingException.classwould retry only via blocking and, if all retries fail, would go straight to the DLT. -
ShouldRetryViaBothException.classwould retry via blocking, and if all blocking retries fail would be forwarded to the next retry topic for another set of attempts. -
ShouldSkipBothRetriesException.classwould never be retried in any way and would go straight to the DLT if the first processing attempt failed.
| Note that the blocking retries behavior is allowlist - you add the exceptions you do want to retry that way; while the non-blocking retries classification is geared towards FATAL exceptions and as such is denylist - you add the exceptions you don’t want to do non-blocking retries, but to send directly to the DLT instead. |
| The non-blocking exception classification behavior also depends on the specific topic’s configuration. |
4.2.7. Accessing Delivery Attempts
To access blocking and non-blocking delivery attempts, add these headers to your @KafkaListener method signature:
@Header(KafkaHeaders.DELIVERY_ATTEMPT) int blockingAttempts,
@Header(name = RetryTopicHeaders.DEFAULT_HEADER_ATTEMPTS, required = false) Integer nonBlockingAttempts
Blocking delivery attempts are only provided if you set ContainerProperties [deliveryAttemptHeader] to true.
Note that the non blocking attempts will be null for the initial delivery.
Starting with version 3.0.10, a convenient KafkaMessageHeaderAccessor is provided to allow simpler access to these headers; the accessor can be provided as a parameter for the listener method:
@RetryableTopic(backoff = @Backoff(...))
@KafkaListener(id = "dh1", topics = "dh1")
void listen(Thing thing, KafkaMessageHeaderAccessor accessor) {
...
}
Use accessor.getBlockingRetryDeliveryAttempt() and accessor.getNonBlockingRetryDeliveryAttempt() to get the values.
The accessor will throw an IllegalStateException if blocking retries are not enabled; for non-blocking retries, the accessor returns 1 for the initial delivery.
4.2.8. Topic Naming
Retry topics and DLT are named by suffixing the main topic with a provided or default value, appended by either the delay or index for that topic.
Examples:
"my-topic" → "my-topic-retry-0", "my-topic-retry-1", …, "my-topic-dlt"
"my-other-topic" → "my-topic-myRetrySuffix-1000", "my-topic-myRetrySuffix-2000", …, "my-topic-myDltSuffix".
The default behavior is to create separate retry topics for each attempt, appended with an index value: retry-0, retry-1, …, retry-n.
Therefore, by default the number of retry topics is the configured maxAttempts minus 1.
|
You can configure the suffixes, choose whether to append the attempt index or delay, use a single retry topic when using fixed backoff, and use a single retry topic for the attempts with the maxInterval when using exponential backoffs.
Retry Topics and Dlt Suffixes
You can specify the suffixes that will be used by the retry and dlt topics.
@RetryableTopic(retryTopicSuffix = "-my-retry-suffix", dltTopicSuffix = "-my-dlt-suffix")
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyOtherPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.retryTopicSuffix("-my-retry-suffix")
.dltTopicSuffix("-my-dlt-suffix")
.create(template);
}
| The default suffixes are "-retry" and "-dlt", for retry topics and dlt respectively. |
Appending the Topic’s Index or Delay
You can either append the topic’s index or delay values after the suffix.
@RetryableTopic(topicSuffixingStrategy = TopicSuffixingStrategy.SUFFIX_WITH_INDEX_VALUE)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.suffixTopicsWithIndexValues()
.create(template);
}
| The default behavior is to suffix with the delay values, except for fixed delay configurations with multiple topics, in which case the topics are suffixed with the topic’s index. |
Single Topic for Fixed Delay Retries
If you’re using fixed delay policies such as FixedBackOffPolicy or NoBackOffPolicy you can use a single topic to accomplish the non-blocking retries.
This topic will be suffixed with the provided or default suffix, and will not have either the index or the delay values appended.
The previous FixedDelayStrategy is now deprecated, and can be replaced by SameIntervalTopicReuseStrategy.
|
@RetryableTopic(backoff = @Backoff(2000), fixedDelayTopicStrategy = FixedDelayStrategy.SINGLE_TOPIC)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.fixedBackoff(3000)
.maxAttempts(5)
.useSingleTopicForFixedDelays()
.create(template);
}
| The default behavior is creating separate retry topics for each attempt, appended with their index value: retry-0, retry-1, … |
Single Topic for maxInterval Exponential Delay
If you’re using exponential backoff policy (ExponentialBackOffPolicy), you can use a single retry topic to accomplish the non-blocking retries of the attempts whose delays are the configured maxInterval.
This "final" retry topic will be suffixed with the provided or default suffix, and will have either the index or the maxInterval value appended.
By opting to use a single topic for the retries with the maxInterval delay, it may become more viable to configure an exponential retry policy that keeps retrying for a long time, because in this approach you do not need a large amount of topics.
|
The default behavior is to work with the number of retry topics equal to the configured maxAttempts minus 1 and, when using exponential backoff, the retry topics are suffixed with the delay values, with the last retry topic (corresponding to the maxInterval delay) being suffixed with an additional index.
For instance, when configuring the exponential backoff with initialInterval=1000, multiplier=2, and maxInterval=16000, in order to keep trying for one hour, one would need to configure maxAttempts as 229, and by default the needed retry topics would be:
-
-retry-1000
-
-retry-2000
-
-retry-4000
-
-retry-8000
-
-retry-16000-0
-
-retry-16000-1
-
-retry-16000-2
-
…
-
-retry-16000-224
When using the strategy that reuses the retry topic for the same intervals, in the same configuration above the needed retry topics would be:
-
-retry-1000
-
-retry-2000
-
-retry-4000
-
-retry-8000
-
-retry-16000
This will be the default in a future release.
@RetryableTopic(attempts = 230,
backoff = @Backoff(delay = 1000, multiplier = 2, maxDelay = 16000),
sameIntervalTopicReuseStrategy = SameIntervalTopicReuseStrategy.SINGLE_TOPIC)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<String, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.exponentialBackoff(1000, 2, 16000)
.maxAttempts(230)
.useSingleTopicForSameIntervals()
.create(template);
}
Custom naming strategies
More complex naming strategies can be accomplished by registering a bean that implements RetryTopicNamesProviderFactory.
The default implementation is SuffixingRetryTopicNamesProviderFactory and a different implementation can be registered in the following way:
@Override
protected RetryTopicComponentFactory createComponentFactory() {
return new RetryTopicComponentFactory() {
@Override
public RetryTopicNamesProviderFactory retryTopicNamesProviderFactory() {
return new CustomRetryTopicNamesProviderFactory();
}
};
}
As an example the following implementation, in addition to the standard suffix, adds a prefix to retry/dl topics names:
public class CustomRetryTopicNamesProviderFactory implements RetryTopicNamesProviderFactory {
@Override
public RetryTopicNamesProvider createRetryTopicNamesProvider(
DestinationTopic.Properties properties) {
if(properties.isMainEndpoint()) {
return new SuffixingRetryTopicNamesProvider(properties);
}
else {
return new SuffixingRetryTopicNamesProvider(properties) {
@Override
public String getTopicName(String topic) {
return "my-prefix-" + super.getTopicName(topic);
}
};
}
}
}
4.2.9. Multiple Listeners, Same Topic(s)
Starting with version 3.0, it is now possible to configure multiple listeners on the same topic(s). In order to do this, you must use custom topic naming to isolate the retry topics from each other. This is best shown with an example:
@RetryableTopic(...
retryTopicSuffix = "-listener1", dltTopicSuffix = "-listener1-dlt",
topicSuffixingStrategy = TopicSuffixingStrategy.SUFFIX_WITH_INDEX_VALUE)
@KafkaListener(id = "listener1", groupId = "group1", topics = TWO_LISTENERS_TOPIC, ...)
void listen1(String message, @Header(KafkaHeaders.RECEIVED_TOPIC) String receivedTopic) {
...
}
@RetryableTopic(...
retryTopicSuffix = "-listener2", dltTopicSuffix = "-listener2-dlt",
topicSuffixingStrategy = TopicSuffixingStrategy.SUFFIX_WITH_INDEX_VALUE)
@KafkaListener(id = "listener2", groupId = "group2", topics = TWO_LISTENERS_TOPIC, ...)
void listen2(String message, @Header(KafkaHeaders.RECEIVED_TOPIC) String receivedTopic) {
...
}
The topicSuffixingStrategy is optional.
The framework will configure and use a separate set of retry topics for each listener.
4.2.10. Dlt Strategies
The framework provides a few strategies for working with DLTs. You can provide a method for DLT processing, use the default logging method, or have no DLT at all. Also you can choose what happens if DLT processing fails.
Dlt Processing Method
You can specify the method used to process the DLT for the topic, as well as the behavior if that processing fails.
To do that you can use the @DltHandler annotation in a method of the class with the @RetryableTopic annotation(s).
Note that the same method will be used for all the @RetryableTopic annotated methods within that class.
@RetryableTopic
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@DltHandler
public void processMessage(MyPojo message) {
// ... message processing, persistence, etc
}
The DLT handler method can also be provided through the RetryTopicConfigurationBuilder.dltHandlerMethod(String, String) method, passing as arguments the bean name and method name that should process the DLT’s messages.
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.dltHandlerMethod("myCustomDltProcessor", "processDltMessage")
.create(template);
}
@Component
public class MyCustomDltProcessor {
private final MyDependency myDependency;
public MyCustomDltProcessor(MyDependency myDependency) {
this.myDependency = myDependency;
}
public void processDltMessage(MyPojo message) {
// ... message processing, persistence, etc
}
}
| If no DLT handler is provided, the default RetryTopicConfigurer.LoggingDltListenerHandlerMethod is used. |
Starting with version 2.8, if you don’t want to consume from the DLT in this application at all, including by the default handler (or you wish to defer consumption), you can control whether or not the DLT container starts, independent of the container factory’s autoStartup property.
When using the @RetryableTopic annotation, set the autoStartDltHandler property to false; when using the configuration builder, use autoStartDltHandler(false) .
You can later start the DLT handler via the KafkaListenerEndpointRegistry.
DLT Failure Behavior
Should the DLT processing fail, there are two possible behaviors available: ALWAYS_RETRY_ON_ERROR and FAIL_ON_ERROR.
In the former the record is forwarded back to the DLT topic so it doesn’t block other DLT records' processing. In the latter the consumer ends the execution without forwarding the message.
@RetryableTopic(dltProcessingFailureStrategy =
DltStrategy.FAIL_ON_ERROR)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.dltHandlerMethod("myCustomDltProcessor", "processDltMessage")
.doNotRetryOnDltFailure()
.create(template);
}
The default behavior is to ALWAYS_RETRY_ON_ERROR.
|
Starting with version 2.8.3, ALWAYS_RETRY_ON_ERROR will NOT route a record back to the DLT if the record causes a fatal exception to be thrown,
such as a DeserializationException because, generally, such exceptions will always be thrown.
|
Exceptions that are considered fatal are:
-
DeserializationException -
MessageConversionException -
ConversionException -
MethodArgumentResolutionException -
NoSuchMethodException -
ClassCastException
You can add exceptions to and remove exceptions from this list using methods on the DestinationTopicResolver bean.
See Exception Classifier for more information.
Configuring No DLT
The framework also provides the possibility of not configuring a DLT for the topic. In this case after retrials are exhausted the processing simply ends.
@RetryableTopic(dltProcessingFailureStrategy =
DltStrategy.NO_DLT)
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.doNotConfigureDlt()
.create(template);
}
4.2.11. Specifying a ListenerContainerFactory
By default the RetryTopic configuration will use the provided factory from the @KafkaListener annotation, but you can specify a different one to be used to create the retry topic and dlt listener containers.
For the @RetryableTopic annotation you can provide the factory’s bean name, and using the RetryTopicConfiguration bean you can either provide the bean name or the instance itself.
@RetryableTopic(listenerContainerFactory = "my-retry-topic-factory")
@KafkaListener(topics = "my-annotated-topic")
public void processMessage(MyPojo message) {
// ... message processing
}
@Bean
public RetryTopicConfiguration myRetryTopic(KafkaTemplate<Integer, MyPojo> template,
ConcurrentKafkaListenerContainerFactory<Integer, MyPojo> factory) {
return RetryTopicConfigurationBuilder
.newInstance()
.listenerFactory(factory)
.create(template);
}
@Bean
public RetryTopicConfiguration myOtherRetryTopic(KafkaTemplate<Integer, MyPojo> template) {
return RetryTopicConfigurationBuilder
.newInstance()
.listenerFactory("my-retry-topic-factory")
.create(template);
}
| Since 2.8.3 you can use the same factory for retryable and non-retryable topics. |
If you need to revert the factory configuration behavior to prior 2.8.3, you can override the configureRetryTopicConfigurer method of a @Configuration class that extends RetryTopicConfigurationSupport as explained in Configuring Global Settings and Features and set useLegacyFactoryConfigurer to true, such as:
@Override
protected Consumer<RetryTopicConfigurer> configureRetryTopicConfigurer() {
return rtc -> rtc.useLegacyFactoryConfigurer(true);
}
4.2.12. Accessing Topics' Information at Runtime
Since 2.9, you can access information regarding the topic chain at runtime by injecting the provided DestinationTopicContainer bean.
This interface provides methods to look up the next topic in the chain or the DLT for a topic if configured, as well as useful properties such as the topic’s name, delay and type.
As a real-world use-case example, you can use such information so a console application can resend a record from the DLT to the first retry topic in the chain after the cause of the failed processing, e.g. bug / inconsistent state, has been resolved.
The DestinationTopic provided by the DestinationTopicContainer#getNextDestinationTopicFor() method corresponds to the next topic registered in the chain for the input topic.
The actual topic the message will be forwarded to may differ due to different factors such as exception classification, number of attempts or single-topic fixed-delay strategies.
Use the DestinationTopicResolver interface if you need to weigh in these factors.
|
4.2.13. Changing KafkaBackOffException Logging Level
When a message in the retry topic is not due for consumption, a KafkaBackOffException is thrown.
Such exceptions are logged by default at DEBUG level, but you can change this behavior by setting an error handler customizer in the ListenerContainerFactoryConfigurer in a @Configuration class.
For example, to change the logging level to WARN you might add:
@Override
protected void configureCustomizers(CustomizersConfigurer customizersConfigurer) {
customizersConfigurer.customizeErrorHandler(defaultErrorHandler ->
defaultErrorHandler.setLogLevel(KafkaException.Level.WARN))
}
4.3. Apache Kafka Streams Support
Starting with version 1.1.4, Spring for Apache Kafka provides first-class support for Kafka Streams.
To use it from a Spring application, the kafka-streams jar must be present on classpath.
It is an optional dependency of the Spring for Apache Kafka project and is not downloaded transitively.
4.3.1. Basics
The reference Apache Kafka Streams documentation suggests the following way of using the API:
// Use the builders to define the actual processing topology, e.g. to specify
// from which input topics to read, which stream operations (filter, map, etc.)
// should be called, and so on.
StreamsBuilder builder = ...; // when using the Kafka Streams DSL
// Use the configuration to tell your application where the Kafka cluster is,
// which serializers/deserializers to use by default, to specify security settings,
// and so on.
StreamsConfig config = ...;
KafkaStreams streams = new KafkaStreams(builder, config);
// Start the Kafka Streams instance
streams.start();
// Stop the Kafka Streams instance
streams.close();
So, we have two main components:
-
StreamsBuilder: With an API to buildKStream(orKTable) instances. -
KafkaStreams: To manage the lifecycle of those instances.
All KStream instances exposed to a KafkaStreams instance by a single StreamsBuilder are started and stopped at the same time, even if they have different logic.
In other words, all streams defined by a StreamsBuilder are tied with a single lifecycle control.
Once a KafkaStreams instance has been closed by streams.close(), it cannot be restarted.
Instead, a new KafkaStreams instance to restart stream processing must be created.
|
4.3.2. Spring Management
To simplify using Kafka Streams from the Spring application context perspective and use the lifecycle management through a container, the Spring for Apache Kafka introduces StreamsBuilderFactoryBean.
This is an AbstractFactoryBean implementation to expose a StreamsBuilder singleton instance as a bean.
The following example creates such a bean:
@Bean
public FactoryBean<StreamsBuilder> myKStreamBuilder(KafkaStreamsConfiguration streamsConfig) {
return new StreamsBuilderFactoryBean(streamsConfig);
}
Starting with version 2.2, the stream configuration is now provided as a KafkaStreamsConfiguration object rather than a StreamsConfig.
|
The StreamsBuilderFactoryBean also implements SmartLifecycle to manage the lifecycle of an internal KafkaStreams instance.
Similar to the Kafka Streams API, you must define the KStream instances before you start the KafkaStreams.
That also applies for the Spring API for Kafka Streams.
Therefore, when you use default autoStartup = true on the StreamsBuilderFactoryBean, you must declare KStream instances on the StreamsBuilder before the application context is refreshed.
For example, KStream can be a regular bean definition, while the Kafka Streams API is used without any impacts.
The following example shows how to do so:
@Bean
public KStream<?, ?> kStream(StreamsBuilder kStreamBuilder) {
KStream<Integer, String> stream = kStreamBuilder.stream(STREAMING_TOPIC1);
// Fluent KStream API
return stream;
}
If you would like to control the lifecycle manually (for example, stopping and starting by some condition), you can reference the StreamsBuilderFactoryBean bean directly by using the factory bean (&) prefix.
Since StreamsBuilderFactoryBean use its internal KafkaStreams instance, it is safe to stop and restart it again.
A new KafkaStreams is created on each start().
You might also consider using different StreamsBuilderFactoryBean instances, if you would like to control the lifecycles for KStream instances separately.
You also can specify KafkaStreams.StateListener, Thread.UncaughtExceptionHandler, and StateRestoreListener options on the StreamsBuilderFactoryBean, which are delegated to the internal KafkaStreams instance.
Also, apart from setting those options indirectly on StreamsBuilderFactoryBean, starting with version 2.1.5, you can use a KafkaStreamsCustomizer callback interface to configure an inner KafkaStreams instance.
Note that KafkaStreamsCustomizer overrides the options provided by StreamsBuilderFactoryBean.
If you need to perform some KafkaStreams operations directly, you can access that internal KafkaStreams instance by using StreamsBuilderFactoryBean.getKafkaStreams().
You can autowire StreamsBuilderFactoryBean bean by type, but you should be sure to use the full type in the bean definition, as the following example shows:
@Bean
public StreamsBuilderFactoryBean myKStreamBuilder(KafkaStreamsConfiguration streamsConfig) {
return new StreamsBuilderFactoryBean(streamsConfig);
}
...
@Autowired
private StreamsBuilderFactoryBean myKStreamBuilderFactoryBean;
Alternatively, you can add @Qualifier for injection by name if you use interface bean definition.
The following example shows how to do so:
@Bean
public FactoryBean<StreamsBuilder> myKStreamBuilder(KafkaStreamsConfiguration streamsConfig) {
return new StreamsBuilderFactoryBean(streamsConfig);
}
...
@Autowired
@Qualifier("&myKStreamBuilder")
private StreamsBuilderFactoryBean myKStreamBuilderFactoryBean;
Starting with version 2.4.1, the factory bean has a new property infrastructureCustomizer with type KafkaStreamsInfrastructureCustomizer; this allows customization of the StreamsBuilder (e.g. to add a state store) and/or the Topology before the stream is created.
public interface KafkaStreamsInfrastructureCustomizer {
void configureBuilder(StreamsBuilder builder);
void configureTopology(Topology topology);
}
Default no-op implementations are provided to avoid having to implement both methods if one is not required.
A CompositeKafkaStreamsInfrastructureCustomizer is provided, for when you need to apply multiple customizers.
4.3.3. KafkaStreams Micrometer Support
Introduced in version 2.5.3, you can configure a KafkaStreamsMicrometerListener to automatically register micrometer meters for the KafkaStreams object managed by the factory bean:
streamsBuilderFactoryBean.addListener(new KafkaStreamsMicrometerListener(meterRegistry,
Collections.singletonList(new ImmutableTag("customTag", "customTagValue"))));
4.3.4. Streams JSON Serialization and Deserialization
For serializing and deserializing data when reading or writing to topics or state stores in JSON format, Spring for Apache Kafka provides a JsonSerde implementation that uses JSON, delegating to the JsonSerializer and JsonDeserializer described in Serialization, Deserialization, and Message Conversion.
The JsonSerde implementation provides the same configuration options through its constructor (target type or ObjectMapper).
In the following example, we use the JsonSerde to serialize and deserialize the Cat payload of a Kafka stream (the JsonSerde can be used in a similar fashion wherever an instance is required):
stream.through(Serdes.Integer(), new JsonSerde<>(Cat.class), "cats");
When constructing the serializer/deserializer programmatically for use in the producer/consumer factory, since version 2.3, you can use the fluent API, which simplifies configuration.
stream.through(new JsonSerde<>(MyKeyType.class)
.forKeys()
.noTypeInfo(),
new JsonSerde<>(MyValueType.class)
.noTypeInfo(),
"myTypes");
4.3.5. Using KafkaStreamBrancher
The KafkaStreamBrancher class introduces a more convenient way to build conditional branches on top of KStream.
Consider the following example that does not use KafkaStreamBrancher:
KStream<String, String>[] branches = builder.stream("source").branch(
(key, value) -> value.contains("A"),
(key, value) -> value.contains("B"),
(key, value) -> true
);
branches[0].to("A");
branches[1].to("B");
branches[2].to("C");
The following example uses KafkaStreamBrancher:
new KafkaStreamBrancher<String, String>()
.branch((key, value) -> value.contains("A"), ks -> ks.to("A"))
.branch((key, value) -> value.contains("B"), ks -> ks.to("B"))
//default branch should not necessarily be defined in the end of the chain!
.defaultBranch(ks -> ks.to("C"))
.onTopOf(builder.stream("source"));
//onTopOf method returns the provided stream so we can continue with method chaining
4.3.6. Configuration
To configure the Kafka Streams environment, the StreamsBuilderFactoryBean requires a KafkaStreamsConfiguration instance.
See the Apache Kafka documentation for all possible options.
Starting with version 2.2, the stream configuration is now provided as a KafkaStreamsConfiguration object, rather than as a StreamsConfig.
|
To avoid boilerplate code for most cases, especially when you develop microservices, Spring for Apache Kafka provides the @EnableKafkaStreams annotation, which you should place on a @Configuration class.
All you need is to declare a KafkaStreamsConfiguration bean named defaultKafkaStreamsConfig.
A StreamsBuilderFactoryBean bean, named defaultKafkaStreamsBuilder, is automatically declared in the application context.
You can declare and use any additional StreamsBuilderFactoryBean beans as well.
You can perform additional customization of that bean, by providing a bean that implements StreamsBuilderFactoryBeanConfigurer.
If there are multiple such beans, they will be applied according to their Ordered.order property.
By default, when the factory bean is stopped, the KafkaStreams.cleanUp() method is called.
Starting with version 2.1.2, the factory bean has additional constructors, taking a CleanupConfig object that has properties to let you control whether the cleanUp() method is called during start() or stop() or neither.
Starting with version 2.7, the default is to never clean up local state.
4.3.7. Header Enricher
Version 3.0 added the HeaderEnricherProcessor extension of ContextualProcessor; providing the same functionality as the deprecated HeaderEnricher which implemented the deprecated Transformer interface.
This can be used to add headers within the stream processing; the header values are SpEL expressions; the root object of the expression evaluation has 3 properties:
-
record- theorg.apache.kafka.streams.processor.api.Record(key,value,timestamp,headers) -
key- the key of the current record -
value- the value of the current record -
context- theProcessorContext, allowing access to the current record metadata
The expressions must return a byte[] or a String (which will be converted to byte[] using UTF-8).
To use the enricher within a stream:
.process(() -> new HeaderEnricherProcessor(expressions))
The processor does not change the key or value; it simply adds headers.
| You need a new instance for each record. |
.process(() -> new HeaderEnricherProcessor<..., ...>(expressionMap))
Here is a simple example, adding one literal header and one variable:
Map<String, Expression> headers = new HashMap<>();
headers.put("header1", new LiteralExpression("value1"));
SpelExpressionParser parser = new SpelExpressionParser();
headers.put("header2", parser.parseExpression("record.timestamp() + ' @' + record.offset()"));
ProcessorSupplier supplier = () -> new HeaderEnricher<String, String> enricher = new HeaderEnricher<>(headers);
KStream<String, String> stream = builder.stream(INPUT);
stream
.process(() -> supplier)
.to(OUTPUT);
4.3.8. MessagingProcessor
Version 3.0 added the MessagingProcessor extension of ContextualProcessor; providing the same functionality as the deprecated MessagingTransformer which implemented the deprecated Transformer interface.
This allows a Kafka Streams topology to interact with a Spring Messaging component, such as a Spring Integration flow.
The transformer requires an implementation of MessagingFunction.
@FunctionalInterface
public interface MessagingFunction {
Message<?> exchange(Message<?> message);
}
Spring Integration automatically provides an implementation using its GatewayProxyFactoryBean.
It also requires a MessagingMessageConverter to convert the key, value and metadata (including headers) to/from a Spring Messaging Message<?>.
See [Calling a Spring Integration Flow from a KStream] for more information.
4.3.9. Recovery from Deserialization Exceptions
Version 2.3 introduced the RecoveringDeserializationExceptionHandler which can take some action when a deserialization exception occurs.
Refer to the Kafka documentation about DeserializationExceptionHandler, of which the RecoveringDeserializationExceptionHandler is an implementation.
The RecoveringDeserializationExceptionHandler is configured with a ConsumerRecordRecoverer implementation.
The framework provides the DeadLetterPublishingRecoverer which sends the failed record to a dead-letter topic.
See Publishing Dead-letter Records for more information about this recoverer.
To configure the recoverer, add the following properties to your streams configuration:
@Bean(name = KafkaStreamsDefaultConfiguration.DEFAULT_STREAMS_CONFIG_BEAN_NAME)
public KafkaStreamsConfiguration kStreamsConfigs() {
Map<String, Object> props = new HashMap<>();
...
props.put(StreamsConfig.DEFAULT_DESERIALIZATION_EXCEPTION_HANDLER_CLASS_CONFIG,
RecoveringDeserializationExceptionHandler.class);
props.put(RecoveringDeserializationExceptionHandler.KSTREAM_DESERIALIZATION_RECOVERER, recoverer());
...
return new KafkaStreamsConfiguration(props);
}
@Bean
public DeadLetterPublishingRecoverer recoverer() {
return new DeadLetterPublishingRecoverer(kafkaTemplate(),
(record, ex) -> new TopicPartition("recovererDLQ", -1));
}
Of course, the recoverer() bean can be your own implementation of ConsumerRecordRecoverer.
4.3.10. Kafka Streams Example
The following example combines all the topics we have covered in this chapter:
@Configuration
@EnableKafka
@EnableKafkaStreams
public static class KafkaStreamsConfig {
@Bean(name = KafkaStreamsDefaultConfiguration.DEFAULT_STREAMS_CONFIG_BEAN_NAME)
public KafkaStreamsConfiguration kStreamsConfigs() {
Map<String, Object> props = new HashMap<>();
props.put(StreamsConfig.APPLICATION_ID_CONFIG, "testStreams");
props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");
props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.Integer().getClass().getName());
props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass().getName());
props.put(StreamsConfig.DEFAULT_TIMESTAMP_EXTRACTOR_CLASS_CONFIG, WallclockTimestampExtractor.class.getName());
return new KafkaStreamsConfiguration(props);
}
@Bean
public StreamsBuilderFactoryBeanConfigurer configurer() {
return fb -> fb.setStateListener((newState, oldState) -> {
System.out.println("State transition from " + oldState + " to " + newState);
});
}
@Bean
public KStream<Integer, String> kStream(StreamsBuilder kStreamBuilder) {
KStream<Integer, String> stream = kStreamBuilder.stream("streamingTopic1");
stream
.mapValues((ValueMapper<String, String>) String::toUpperCase)
.groupByKey()
.windowedBy(TimeWindows.of(Duration.ofMillis(1000)))
.reduce((String value1, String value2) -> value1 + value2,
Named.as("windowStore"))
.toStream()
.map((windowedId, value) -> new KeyValue<>(windowedId.key(), value))
.filter((i, s) -> s.length() > 40)
.to("streamingTopic2");
stream.print(Printed.toSysOut());
return stream;
}
}
4.4. Testing Applications
The spring-kafka-test jar contains some useful utilities to assist with testing your applications.
4.4.1. KafkaTestUtils
o.s.kafka.test.utils.KafkaTestUtils provides a number of static helper methods to consume records, retrieve various record offsets, and others.
Refer to its Javadocs for complete details.
4.4.2. JUnit
o.s.kafka.test.utils.KafkaTestUtils also provides some static methods to set up producer and consumer properties.
The following listing shows those method signatures:
/**
* Set up test properties for an {@code <Integer, String>} consumer.
* @param group the group id.
* @param autoCommit the auto commit.
* @param embeddedKafka a {@link EmbeddedKafkaBroker} instance.
* @return the properties.
*/
public static Map<String, Object> consumerProps(String group, String autoCommit,
EmbeddedKafkaBroker embeddedKafka) { ... }
/**
* Set up test properties for an {@code <Integer, String>} producer.
* @param embeddedKafka a {@link EmbeddedKafkaBroker} instance.
* @return the properties.
*/
public static Map<String, Object> producerProps(EmbeddedKafkaBroker embeddedKafka) { ... }
|
Starting with version 2.5, the When using the embedded broker, it is generally best practice using a different topic for each test, to prevent cross-talk.
If this is not possible for some reason, note that the |
A JUnit 4 @Rule wrapper for the EmbeddedKafkaBroker is provided to create an embedded Kafka and an embedded Zookeeper server.
(See @EmbeddedKafka Annotation for information about using @EmbeddedKafka with JUnit 5).
The following listing shows the signatures of those methods:
/**
* Create embedded Kafka brokers.
* @param count the number of brokers.
* @param controlledShutdown passed into TestUtils.createBrokerConfig.
* @param topics the topics to create (2 partitions per).
*/
public EmbeddedKafkaRule(int count, boolean controlledShutdown, String... topics) { ... }
/**
*
* Create embedded Kafka brokers.
* @param count the number of brokers.
* @param controlledShutdown passed into TestUtils.createBrokerConfig.
* @param partitions partitions per topic.
* @param topics the topics to create.
*/
public EmbeddedKafkaRule(int count, boolean controlledShutdown, int partitions, String... topics) { ... }
The EmbeddedKafkaBroker class has a utility method that lets you consume for all the topics it created.
The following example shows how to use it:
Map<String, Object> consumerProps = KafkaTestUtils.consumerProps("testT", "false", embeddedKafka);
DefaultKafkaConsumerFactory<Integer, String> cf = new DefaultKafkaConsumerFactory<Integer, String>(
consumerProps);
Consumer<Integer, String> consumer = cf.createConsumer();
embeddedKafka.consumeFromAllEmbeddedTopics(consumer);
The KafkaTestUtils has some utility methods to fetch results from the consumer.
The following listing shows those method signatures:
/**
* Poll the consumer, expecting a single record for the specified topic.
* @param consumer the consumer.
* @param topic the topic.
* @return the record.
* @throws org.junit.ComparisonFailure if exactly one record is not received.
*/
public static <K, V> ConsumerRecord<K, V> getSingleRecord(Consumer<K, V> consumer, String topic) { ... }
/**
* Poll the consumer for records.
* @param consumer the consumer.
* @return the records.
*/
public static <K, V> ConsumerRecords<K, V> getRecords(Consumer<K, V> consumer) { ... }
The following example shows how to use KafkaTestUtils:
...
template.sendDefault(0, 2, "bar");
ConsumerRecord<Integer, String> received = KafkaTestUtils.getSingleRecord(consumer, "topic");
...
When the embedded Kafka and embedded Zookeeper server are started by the EmbeddedKafkaBroker, a system property named spring.embedded.kafka.brokers is set to the address of the Kafka brokers and a system property named spring.embedded.zookeeper.connect is set to the address of Zookeeper.
Convenient constants (EmbeddedKafkaBroker.SPRING_EMBEDDED_KAFKA_BROKERS and EmbeddedKafkaBroker.SPRING_EMBEDDED_ZOOKEEPER_CONNECT) are provided for this property.
Instead of default spring.embedded.kafka.brokers system property, the address of the Kafka brokers can be exposed to any arbitrary and convenient property.
For this purpose a spring.embedded.kafka.brokers.property (EmbeddedKafkaBroker.BROKER_LIST_PROPERTY) system property can be set before starting an embedded Kafka.
For example, with Spring Boot a spring.kafka.bootstrap-servers configuration property is expected to be set for auto-configuring Kafka client, respectively.
So, before running tests with an embedded Kafka on random ports, we can set spring.embedded.kafka.brokers.property=spring.kafka.bootstrap-servers as a system property - and the EmbeddedKafkaBroker will use it to expose its broker addresses.
This is now the default value for this property (starting with version 3.0.10).
With the EmbeddedKafkaBroker.brokerProperties(Map<String, String>), you can provide additional properties for the Kafka servers.
See Kafka Config for more information about possible broker properties.
4.4.3. Configuring Topics
The following example configuration creates topics called cat and hat with five partitions, a topic called thing1 with 10 partitions, and a topic called thing2 with 15 partitions:
public class MyTests {
@ClassRule
private static EmbeddedKafkaRule embeddedKafka = new EmbeddedKafkaRule(1, false, 5, "cat", "hat");
@Test
public void test() {
embeddedKafkaRule.getEmbeddedKafka()
.addTopics(new NewTopic("thing1", 10, (short) 1), new NewTopic("thing2", 15, (short) 1));
...
}
}
By default, addTopics will throw an exception when problems arise (such as adding a topic that already exists).
Version 2.6 added a new version of that method that returns a Map<String, Exception>; the key is the topic name and the value is null for success, or an Exception for a failure.
4.4.4. Using the Same Broker(s) for Multiple Test Classes
You can use the same broker for multiple test classes with something similar to the following:
public final class EmbeddedKafkaHolder {
private static EmbeddedKafkaBroker embeddedKafka = new EmbeddedKafkaBroker(1, false)
.brokerListProperty("spring.kafka.bootstrap-servers");
private static boolean started;
public static EmbeddedKafkaBroker getEmbeddedKafka() {
if (!started) {
try {
embeddedKafka.afterPropertiesSet();
}
catch (Exception e) {
throw new KafkaException("Embedded broker failed to start", e);
}
started = true;
}
return embeddedKafka;
}
private EmbeddedKafkaHolder() {
super();
}
}
This assumes a Spring Boot environment and the embedded broker replaces the bootstrap servers property.
Then, in each test class, you can use something similar to the following:
static {
EmbeddedKafkaHolder.getEmbeddedKafka().addTopics("topic1", "topic2");
}
private static final EmbeddedKafkaBroker broker = EmbeddedKafkaHolder.getEmbeddedKafka();
If you are not using Spring Boot, you can obtain the bootstrap servers using broker.getBrokersAsString().
The preceding example provides no mechanism for shutting down the broker(s) when all tests are complete.
This could be a problem if, say, you run your tests in a Gradle daemon.
You should not use this technique in such a situation, or you should use something to call destroy() on the EmbeddedKafkaBroker when your tests are complete.
|
Starting with version 3.0, the framework exposes a GlobalEmbeddedKafkaTestExecutionListener for the JUnit Platform; it is disabled by default.
This requires JUnit Platform 1.8 or greater.
The purpose of this listener is to start one global EmbeddedKafkaBroker for the whole test plan and stop it at the end of the plan.
To enable this listener, and therefore have a single global embedded Kafka cluster for all the tests in the project, the spring.kafka.global.embedded.enabled property must be set to true via system properties or JUnit Platform configuration.
In addition, these properties can be provided:
-
spring.kafka.embedded.count- the number of Kafka brokers to manage; -
spring.kafka.embedded.ports- ports (comma-separated value) for every Kafka broker to start,0if random port is a preferred; the number of values must be equal to thecountmentioned above; -
spring.kafka.embedded.topics- topics (comma-separated value) to create in the started Kafka cluster; -
spring.kafka.embedded.partitions- number of partitions to provision for the created topics; -
spring.kafka.embedded.broker.properties.location- the location of the file for additional Kafka broker configuration properties; the value of this property must follow the Spring resource abstraction pattern.
Essentially these properties mimic some of the @EmbeddedKafka attributes.
See more information about configuration properties and how to provide them in the JUnit 5 User Guide.
For example, a spring.embedded.kafka.brokers.property=my.bootstrap-servers entry can be added into a junit-platform.properties file in the testing classpath.
Starting with version 3.0.10, the broker automatically sets this to spring.kafka.bootstrap-servers, by default, for testing with Spring Boot applications.
| It is recommended to not combine a global embedded Kafka and per-test class in a single test suite. Both of them share the same system properties, so it is very likely going to lead to unexpected behavior. |
spring-kafka-test has transitive dependencies on junit-jupiter-api and junit-platform-launcher (the latter to support the global embedded broker).
If you wish to use the embedded broker and are NOT using JUnit, you may wish to exclude these dependencies.
|
4.4.5. @EmbeddedKafka Annotation
We generally recommend that you use the rule as a @ClassRule to avoid starting and stopping the broker between tests (and use a different topic for each test).
Starting with version 2.0, if you use Spring’s test application context caching, you can also declare a EmbeddedKafkaBroker bean, so a single broker can be used across multiple test classes.
For convenience, we provide a test class-level annotation called @EmbeddedKafka to register the EmbeddedKafkaBroker bean.
The following example shows how to use it:
@RunWith(SpringRunner.class)
@DirtiesContext
@EmbeddedKafka(partitions = 1,
topics = {
KafkaStreamsTests.STREAMING_TOPIC1,
KafkaStreamsTests.STREAMING_TOPIC2 })
public class KafkaStreamsTests {
@Autowired
private EmbeddedKafkaBroker embeddedKafka;
@Test
public void someTest() {
Map<String, Object> consumerProps = KafkaTestUtils.consumerProps("testGroup", "true", this.embeddedKafka);
consumerProps.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
ConsumerFactory<Integer, String> cf = new DefaultKafkaConsumerFactory<>(consumerProps);
Consumer<Integer, String> consumer = cf.createConsumer();
this.embeddedKafka.consumeFromAnEmbeddedTopic(consumer, KafkaStreamsTests.STREAMING_TOPIC2);
ConsumerRecords<Integer, String> replies = KafkaTestUtils.getRecords(consumer);
assertThat(replies.count()).isGreaterThanOrEqualTo(1);
}
@Configuration
@EnableKafkaStreams
public static class KafkaStreamsConfiguration {
@Value("${" + EmbeddedKafkaBroker.SPRING_EMBEDDED_KAFKA_BROKERS + "}")
private String brokerAddresses;
@Bean(name = KafkaStreamsDefaultConfiguration.DEFAULT_STREAMS_CONFIG_BEAN_NAME)
public KafkaStreamsConfiguration kStreamsConfigs() {
Map<String, Object> props = new HashMap<>();
props.put(StreamsConfig.APPLICATION_ID_CONFIG, "testStreams");
props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, this.brokerAddresses);
return new KafkaStreamsConfiguration(props);
}
}
}
Starting with version 2.2.4, you can also use the @EmbeddedKafka annotation to specify the Kafka ports property.
The following example sets the topics, brokerProperties, and brokerPropertiesLocation attributes of @EmbeddedKafka support property placeholder resolutions:
@TestPropertySource(locations = "classpath:/test.properties")
@EmbeddedKafka(topics = { "any-topic", "${kafka.topics.another-topic}" },
brokerProperties = { "log.dir=${kafka.broker.logs-dir}",
"listeners=PLAINTEXT://localhost:${kafka.broker.port}",
"auto.create.topics.enable=${kafka.broker.topics-enable:true}" },
brokerPropertiesLocation = "classpath:/broker.properties")
In the preceding example, the property placeholders ${kafka.topics.another-topic}, ${kafka.broker.logs-dir}, and ${kafka.broker.port} are resolved from the Spring Environment.
In addition, the broker properties are loaded from the broker.properties classpath resource specified by the brokerPropertiesLocation.
Property placeholders are resolved for the brokerPropertiesLocation URL and for any property placeholders found in the resource.
Properties defined by brokerProperties override properties found in brokerPropertiesLocation.
You can use the @EmbeddedKafka annotation with JUnit 4 or JUnit 5.
4.4.6. @EmbeddedKafka Annotation with JUnit5
Starting with version 2.3, there are two ways to use the @EmbeddedKafka annotation with JUnit5.
When used with the @SpringJunitConfig annotation, the embedded broker is added to the test application context.
You can auto wire the broker into your test, at the class or method level, to get the broker address list.
When not using the spring test context, the EmbdeddedKafkaCondition creates a broker; the condition includes a parameter resolver so you can access the broker in your test method…
@EmbeddedKafka
public class EmbeddedKafkaConditionTests {
@Test
public void test(EmbeddedKafkaBroker broker) {
String brokerList = broker.getBrokersAsString();
...
}
}
A stand-alone (not Spring test context) broker will be created if the class annotated with @EmbeddedBroker is not also annotated (or meta annotated) with ExtendedWith(SpringExtension.class).
@SpringJunitConfig and @SpringBootTest are so meta annotated and the context-based broker will be used when either of those annotations are also present.
| When there is a Spring test application context available, the topics and broker properties can contain property placeholders, which will be resolved as long as the property is defined somewhere. If there is no Spring context available, these placeholders won’t be resolved. |
4.4.7. Embedded Broker in @SpringBootTest Annotations
Spring Initializr now automatically adds the spring-kafka-test dependency in test scope to the project configuration.
|
If your application uses the Kafka binder in |
There are several ways to use an embedded broker in a Spring Boot application test.
They include:
JUnit4 Class Rule
The following example shows how to use a JUnit4 class rule to create an embedded broker:
@RunWith(SpringRunner.class)
@SpringBootTest
public class MyApplicationTests {
@ClassRule
public static EmbeddedKafkaRule broker = new EmbeddedKafkaRule(1,
false, "someTopic")
.brokerListProperty("spring.kafka.bootstrap-servers");
}
@Autowired
private KafkaTemplate<String, String> template;
@Test
public void test() {
...
}
}
Notice that, since this is a Spring Boot application, we override the broker list property to set Boot’s property.
@EmbeddedKafka Annotation or EmbeddedKafkaBroker Bean
The following example shows how to use an @EmbeddedKafka Annotation to create an embedded broker:
@RunWith(SpringRunner.class)
@EmbeddedKafka(topics = "someTopic",
bootstrapServersProperty = "spring.kafka.bootstrap-servers") // this is now the default
public class MyApplicationTests {
@Autowired
private KafkaTemplate<String, String> template;
@Test
public void test() {
...
}
}
The bootstrapServersProperty is automatically set to spring.kafka.bootstrap-servers, by default, starting with version 3.0.10.
|
4.4.8. Hamcrest Matchers
The o.s.kafka.test.hamcrest.KafkaMatchers provides the following matchers:
/**
* @param key the key
* @param <K> the type.
* @return a Matcher that matches the key in a consumer record.
*/
public static <K> Matcher<ConsumerRecord<K, ?>> hasKey(K key) { ... }
/**
* @param value the value.
* @param <V> the type.
* @return a Matcher that matches the value in a consumer record.
*/
public static <V> Matcher<ConsumerRecord<?, V>> hasValue(V value) { ... }
/**
* @param partition the partition.
* @return a Matcher that matches the partition in a consumer record.
*/
public static Matcher<ConsumerRecord<?, ?>> hasPartition(int partition) { ... }
/**
* Matcher testing the timestamp of a {@link ConsumerRecord} assuming the topic has been set with
* {@link org.apache.kafka.common.record.TimestampType#CREATE_TIME CreateTime}.
*
* @param ts timestamp of the consumer record.
* @return a Matcher that matches the timestamp in a consumer record.
*/
public static Matcher<ConsumerRecord<?, ?>> hasTimestamp(long ts) {
return hasTimestamp(TimestampType.CREATE_TIME, ts);
}
/**
* Matcher testing the timestamp of a {@link ConsumerRecord}
* @param type timestamp type of the record
* @param ts timestamp of the consumer record.
* @return a Matcher that matches the timestamp in a consumer record.
*/
public static Matcher<ConsumerRecord<?, ?>> hasTimestamp(TimestampType type, long ts) {
return new ConsumerRecordTimestampMatcher(type, ts);
}
4.4.9. AssertJ Conditions
You can use the following AssertJ conditions:
/**
* @param key the key
* @param <K> the type.
* @return a Condition that matches the key in a consumer record.
*/
public static <K> Condition<ConsumerRecord<K, ?>> key(K key) { ... }
/**
* @param value the value.
* @param <V> the type.
* @return a Condition that matches the value in a consumer record.
*/
public static <V> Condition<ConsumerRecord<?, V>> value(V value) { ... }
/**
* @param key the key.
* @param value the value.
* @param <K> the key type.
* @param <V> the value type.
* @return a Condition that matches the key in a consumer record.
* @since 2.2.12
*/
public static <K, V> Condition<ConsumerRecord<K, V>> keyValue(K key, V value) { ... }
/**
* @param partition the partition.
* @return a Condition that matches the partition in a consumer record.
*/
public static Condition<ConsumerRecord<?, ?>> partition(int partition) { ... }
/**
* @param value the timestamp.
* @return a Condition that matches the timestamp value in a consumer record.
*/
public static Condition<ConsumerRecord<?, ?>> timestamp(long value) {
return new ConsumerRecordTimestampCondition(TimestampType.CREATE_TIME, value);
}
/**
* @param type the type of timestamp
* @param value the timestamp.
* @return a Condition that matches the timestamp value in a consumer record.
*/
public static Condition<ConsumerRecord<?, ?>> timestamp(TimestampType type, long value) {
return new ConsumerRecordTimestampCondition(type, value);
}
4.4.10. Example
The following example brings together most of the topics covered in this chapter:
public class KafkaTemplateTests {
private static final String TEMPLATE_TOPIC = "templateTopic";
@ClassRule
public static EmbeddedKafkaRule embeddedKafka = new EmbeddedKafkaRule(1, true, TEMPLATE_TOPIC);
@Test
public void testTemplate() throws Exception {
Map<String, Object> consumerProps = KafkaTestUtils.consumerProps("testT", "false",
embeddedKafka.getEmbeddedKafka());
DefaultKafkaConsumerFactory<Integer, String> cf =
new DefaultKafkaConsumerFactory<Integer, String>(consumerProps);
ContainerProperties containerProperties = new ContainerProperties(TEMPLATE_TOPIC);
KafkaMessageListenerContainer<Integer, String> container =
new KafkaMessageListenerContainer<>(cf, containerProperties);
final BlockingQueue<ConsumerRecord<Integer, String>> records = new LinkedBlockingQueue<>();
container.setupMessageListener(new MessageListener<Integer, String>() {
@Override
public void onMessage(ConsumerRecord<Integer, String> record) {
System.out.println(record);
records.add(record);
}
});
container.setBeanName("templateTests");
container.start();
ContainerTestUtils.waitForAssignment(container,
embeddedKafka.getEmbeddedKafka().getPartitionsPerTopic());
Map<String, Object> producerProps =
KafkaTestUtils.producerProps(embeddedKafka.getEmbeddedKafka());
ProducerFactory<Integer, String> pf =
new DefaultKafkaProducerFactory<Integer, String>(producerProps);
KafkaTemplate<Integer, String> template = new KafkaTemplate<>(pf);
template.setDefaultTopic(TEMPLATE_TOPIC);
template.sendDefault("foo");
assertThat(records.poll(10, TimeUnit.SECONDS), hasValue("foo"));
template.sendDefault(0, 2, "bar");
ConsumerRecord<Integer, String> received = records.poll(10, TimeUnit.SECONDS);
assertThat(received, hasKey(2));
assertThat(received, hasPartition(0));
assertThat(received, hasValue("bar"));
template.send(TEMPLATE_TOPIC, 0, 2, "baz");
received = records.poll(10, TimeUnit.SECONDS);
assertThat(received, hasKey(2));
assertThat(received, hasPartition(0));
assertThat(received, hasValue("baz"));
}
}
The preceding example uses the Hamcrest matchers.
With AssertJ, the final part looks like the following code:
assertThat(records.poll(10, TimeUnit.SECONDS)).has(value("foo"));
template.sendDefault(0, 2, "bar");
ConsumerRecord<Integer, String> received = records.poll(10, TimeUnit.SECONDS);
// using individual assertions
assertThat(received).has(key(2));
assertThat(received).has(value("bar"));
assertThat(received).has(partition(0));
template.send(TEMPLATE_TOPIC, 0, 2, "baz");
received = records.poll(10, TimeUnit.SECONDS);
// using allOf()
assertThat(received).has(allOf(keyValue(2, "baz"), partition(0)));
4.4.11. Mock Consumer and Producer
The kafka-clients library provides MockConsumer and MockProducer classes for testing purposes.
If you wish to use these classes in some of your tests with listener containers or KafkaTemplate respectively, starting with version 3.0.7, the framework now provides MockConsumerFactory and MockProducerFactory implementations.
These factories can be used in the listener container and template instead of the default factories, which require a running (or embedded) broker.
Here is an example of a simple implementation returning a single consumer:
@Bean
ConsumerFactory<String, String> consumerFactory() {
MockConsumer<String, String> consumer = new MockConsumer<>(OffsetResetStrategy.EARLIEST);
TopicPartition topicPartition0 = new TopicPartition("topic", 0);
List<TopicPartition> topicPartitions = Arrays.asList(topicPartition0);
Map<TopicPartition, Long> beginningOffsets = topicPartitions.stream().collect(Collectors
.toMap(Function.identity(), tp -> 0L));
consumer.updateBeginningOffsets(beginningOffsets);
consumer.schedulePollTask(() -> {
consumer.addRecord(
new ConsumerRecord<>("topic", 0, 0L, 0L, TimestampType.NO_TIMESTAMP_TYPE, 0, 0, null, "test1",
new RecordHeaders(), Optional.empty()));
consumer.addRecord(
new ConsumerRecord<>("topic", 0, 1L, 0L, TimestampType.NO_TIMESTAMP_TYPE, 0, 0, null, "test2",
new RecordHeaders(), Optional.empty()));
});
return new MockConsumerFactory(() -> consumer);
}
If you wish to test with concurrency, the Supplier lambda in the factory’s constructor would need create a new instance each time.
With the MockProducerFactory, there are two constructors; one to create a simple factory, and one to create factory that supports transactions.
Here are examples:
@Bean
ProducerFactory<String, String> nonTransFactory() {
return new MockProducerFactory<>(() ->
new MockProducer<>(true, new StringSerializer(), new StringSerializer()));
}
@Bean
ProducerFactory<String, String> transFactory() {
MockProducer<String, String> mockProducer =
new MockProducer<>(true, new StringSerializer(), new StringSerializer());
mockProducer.initTransactions();
return new MockProducerFactory<String, String>((tx, id) -> mockProducer, "defaultTxId");
}
Notice in the second case, the lambda is a BiFunction<Boolean, String> where the first parameter is true if the caller wants a transactional producer; the optional second parameter contains the transactional id.
This can be the default (as provided in the constructor), or can be overridden by the KafkaTransactionManager (or KafkaTemplate for local transactions), if so configured.
The transactional id is provided in case you wish to use a different MockProducer based on this value.
If you are using producers in a multi-threaded environment, the BiFunction should return multiple producers (perhaps thread-bound using a ThreadLocal).
Transactional MockProducer s must be initialized for transactions by calling initTransaction().
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