Item Reader and Writer Implementations
In this section, we will introduce you to readers and writers that have not already been discussed in the previous sections.
Decorators
In some cases, a user needs specialized behavior to be appended to a pre-existing
ItemReader. Spring Batch offers some out of the box decorators that can add
additional behavior to to your ItemReader and ItemWriter implementations.
Spring Batch includes the following decorators:
SynchronizedItemStreamReader
When using an ItemReader that is not thread safe, Spring Batch offers the
SynchronizedItemStreamReader decorator, which can be used to make the ItemReader
thread safe. Spring Batch provides a SynchronizedItemStreamReaderBuilder to construct
an instance of the SynchronizedItemStreamReader.
For example, the FlatFileItemReader is not thread-safe and cannot be used in
a multi-threaded step. This reader can be decorated with a SynchronizedItemStreamReader
in order to use it safely in a multi-threaded step. Here is an example of how to decorate
such a reader:
@Bean
public SynchronizedItemStreamReader<Person> itemReader() {
FlatFileItemReader<Person> flatFileItemReader = new FlatFileItemReaderBuilder<Person>()
// set reader properties
.build();
return new SynchronizedItemStreamReaderBuilder<Person>()
.delegate(flatFileItemReader)
.build();
}SingleItemPeekableItemReader
Spring Batch includes a decorator that adds a peek method to an ItemReader. This peek
method lets the user peek one item ahead. Repeated calls to the peek returns the same
item, and this is the next item returned from the read method. Spring Batch provides a
SingleItemPeekableItemReaderBuilder to construct an instance of the
SingleItemPeekableItemReader.
| SingleItemPeekableItemReader’s peek method is not thread-safe, because it would not be possible to honor the peek in multiple threads. Only one of the threads that peeked would get that item in the next call to read. |
SynchronizedItemStreamWriter
When using an ItemWriter that is not thread safe, Spring Batch offers the
SynchronizedItemStreamWriter decorator, which can be used to make the ItemWriter
thread safe. Spring Batch provides a SynchronizedItemStreamWriterBuilder to construct
an instance of the SynchronizedItemStreamWriter.
For example, the FlatFileItemWriter is not thread-safe and cannot be used in
a multi-threaded step. This writer can be decorated with a SynchronizedItemStreamWriter
in order to use it safely in a multi-threaded step. Here is an example of how to decorate
such a writer:
@Bean
public SynchronizedItemStreamWriter<Person> itemWriter() {
FlatFileItemWriter<Person> flatFileItemWriter = new FlatFileItemWriterBuilder<Person>()
// set writer properties
.build();
return new SynchronizedItemStreamWriterBuilder<Person>()
.delegate(flatFileItemWriter)
.build();
}MultiResourceItemWriter
The MultiResourceItemWriter wraps a ResourceAwareItemWriterItemStream and creates a new
output resource when the count of items written in the current resource exceeds the
itemCountLimitPerResource. Spring Batch provides a MultiResourceItemWriterBuilder to
construct an instance of the MultiResourceItemWriter.
ClassifierCompositeItemWriter
The ClassifierCompositeItemWriter calls one of a collection of ItemWriter
implementations for each item, based on a router pattern implemented through the provided
Classifier. The implementation is thread-safe if all delegates are thread-safe. Spring
Batch provides a ClassifierCompositeItemWriterBuilder to construct an instance of the
ClassifierCompositeItemWriter.
ClassifierCompositeItemProcessor
The ClassifierCompositeItemProcessor is an ItemProcessor that calls one of a
collection of ItemProcessor implementations, based on a router pattern implemented
through the provided Classifier. Spring Batch provides a
ClassifierCompositeItemProcessorBuilder to construct an instance of the
ClassifierCompositeItemProcessor.
Messaging Readers And Writers
Spring Batch offers the following readers and writers for commonly used messaging systems:
AmqpItemReader
The AmqpItemReader is an ItemReader that uses an AmqpTemplate to receive or convert
messages from an exchange. Spring Batch provides a AmqpItemReaderBuilder to construct
an instance of the AmqpItemReader.
AmqpItemWriter
The AmqpItemWriter is an ItemWriter that uses an AmqpTemplate to send messages to
an AMQP exchange. Messages are sent to the nameless exchange if the name not specified in
the provided AmqpTemplate. Spring Batch provides an AmqpItemWriterBuilder to
construct an instance of the AmqpItemWriter.
JmsItemReader
The JmsItemReader is an ItemReader for JMS that uses a JmsTemplate. The template
should have a default destination, which is used to provide items for the read()
method. Spring Batch provides a JmsItemReaderBuilder to construct an instance of the
JmsItemReader.
JmsItemWriter
The JmsItemWriter is an ItemWriter for JMS that uses a JmsTemplate. The template
should have a default destination, which is used to send items in write(List). Spring
Batch provides a JmsItemWriterBuilder to construct an instance of the JmsItemWriter.
KafkaItemReader
The KafkaItemReader is an ItemReader for an Apache Kafka topic. It can be configured
to read messages from multiple partitions of the same topic. It stores message offsets
in the execution context to support restart capabilities. Spring Batch provides a
KafkaItemReaderBuilder to construct an instance of the KafkaItemReader.
Database Readers
Spring Batch offers the following database readers:
Neo4jItemReader
The Neo4jItemReader is an ItemReader that reads objects from the graph database Neo4j
by using a paging technique. Spring Batch provides a Neo4jItemReaderBuilder to
construct an instance of the Neo4jItemReader.
Database Writers
Spring Batch offers the following database writers:
Neo4jItemWriter
The Neo4jItemWriter is an ItemWriter implementation that writes to a Neo4j database.
Spring Batch provides a Neo4jItemWriterBuilder to construct an instance of the
Neo4jItemWriter.
MongoItemWriter
The MongoItemWriter is an ItemWriter implementation that writes to a MongoDB store
using an implementation of Spring Data’s MongoOperations. Spring Batch provides a
MongoItemWriterBuilder to construct an instance of the MongoItemWriter.
RepositoryItemWriter
The RepositoryItemWriter is an ItemWriter wrapper for a CrudRepository from Spring
Data. Spring Batch provides a RepositoryItemWriterBuilder to construct an instance of
the RepositoryItemWriter.
Specialized Readers
Spring Batch offers the following specialized readers:
LdifReader
The LdifReader reads LDIF (LDAP Data Interchange Format) records from a Resource,
parses them, and returns a LdapAttribute object for each read executed. Spring Batch
provides a LdifReaderBuilder to construct an instance of the LdifReader.
MappingLdifReader
The MappingLdifReader reads LDIF (LDAP Data Interchange Format) records from a
Resource, parses them then maps each LDIF record to a POJO (Plain Old Java Object).
Each read returns a POJO. Spring Batch provides a MappingLdifReaderBuilder to construct
an instance of the MappingLdifReader.
AvroItemReader
The AvroItemReader reads serialized Avro data from a Resource.
Each read returns an instance of the type specified by a Java class or Avro Schema.
The reader may be optionally configured for input that embeds an Avro schema or not.
Spring Batch provides an AvroItemReaderBuilder to construct an instance of the AvroItemReader.
Specialized Writers
Spring Batch offers the following specialized writers: