Core Features
1. SpringApplication
The SpringApplication class provides a convenient way to bootstrap a Spring application that is started from a main() method.
In many situations, you can delegate to the static SpringApplication.run method, as shown in the following example:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args)
}
When your application starts, you should see something similar to the following output:
. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v3.2.12) 2024-11-21T07:54:31.952Z INFO 109723 --- [ main] o.s.b.d.f.logexample.MyApplication : Starting MyApplication using Java 17.0.13 with PID 109723 (/opt/apps/myapp.jar started by myuser in /opt/apps/) 2024-11-21T07:54:31.973Z INFO 109723 --- [ main] o.s.b.d.f.logexample.MyApplication : No active profile set, falling back to 1 default profile: "default" 2024-11-21T07:54:35.091Z INFO 109723 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port 8080 (http) 2024-11-21T07:54:35.118Z INFO 109723 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2024-11-21T07:54:35.118Z INFO 109723 --- [ main] o.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/10.1.33] 2024-11-21T07:54:35.256Z INFO 109723 --- [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2024-11-21T07:54:35.260Z INFO 109723 --- [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 3064 ms 2024-11-21T07:54:36.449Z INFO 109723 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port 8080 (http) with context path '' 2024-11-21T07:54:36.470Z INFO 109723 --- [ main] o.s.b.d.f.logexample.MyApplication : Started MyApplication in 5.778 seconds (process running for 6.606)
By default, INFO logging messages are shown, including some relevant startup details, such as the user that launched the application.
If you need a log level other than INFO, you can set it, as described in Log Levels.
The application version is determined using the implementation version from the main application class’s package.
Startup information logging can be turned off by setting spring.main.log-startup-info to false.
This will also turn off logging of the application’s active profiles.
To add additional logging during startup, you can override logStartupInfo(boolean) in a subclass of SpringApplication.
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1.1. Startup Failure
If your application fails to start, registered FailureAnalyzers get a chance to provide a dedicated error message and a concrete action to fix the problem.
For instance, if you start a web application on port 8080 and that port is already in use, you should see something similar to the following message:
*************************** APPLICATION FAILED TO START *************************** Description: Embedded servlet container failed to start. Port 8080 was already in use. Action: Identify and stop the process that is listening on port 8080 or configure this application to listen on another port.
Spring Boot provides numerous FailureAnalyzer implementations, and you can add your own.
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If no failure analyzers are able to handle the exception, you can still display the full conditions report to better understand what went wrong.
To do so, you need to enable the debug property or enable DEBUG logging for org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener.
For instance, if you are running your application by using java -jar, you can enable the debug property as follows:
$ java -jar myproject-0.0.1-SNAPSHOT.jar --debug1.2. Lazy Initialization
SpringApplication allows an application to be initialized lazily.
When lazy initialization is enabled, beans are created as they are needed rather than during application startup.
As a result, enabling lazy initialization can reduce the time that it takes your application to start.
In a web application, enabling lazy initialization will result in many web-related beans not being initialized until an HTTP request is received.
A downside of lazy initialization is that it can delay the discovery of a problem with the application. If a misconfigured bean is initialized lazily, a failure will no longer occur during startup and the problem will only become apparent when the bean is initialized. Care must also be taken to ensure that the JVM has sufficient memory to accommodate all of the application’s beans and not just those that are initialized during startup. For these reasons, lazy initialization is not enabled by default and it is recommended that fine-tuning of the JVM’s heap size is done before enabling lazy initialization.
Lazy initialization can be enabled programmatically using the lazyInitialization method on SpringApplicationBuilder or the setLazyInitialization method on SpringApplication.
Alternatively, it can be enabled using the spring.main.lazy-initialization property as shown in the following example:
spring.main.lazy-initialization=truespring:
main:
lazy-initialization: true
If you want to disable lazy initialization for certain beans while using lazy initialization for the rest of the application, you can explicitly set their lazy attribute to false using the @Lazy(false) annotation.
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1.3. Customizing the Banner
The banner that is printed on start up can be changed by adding a banner.txt file to your classpath or by setting the spring.banner.location property to the location of such a file.
If the file has an encoding other than UTF-8, you can set spring.banner.charset.
Inside your banner.txt file, you can use any key available in the Environment as well as any of the following placeholders:
| Variable | Description |
|---|---|
|
The version number of your application, as declared in |
|
The version number of your application, as declared in |
|
The Spring Boot version that you are using.
For example |
|
The Spring Boot version that you are using, formatted for display (surrounded with brackets and prefixed with |
|
Where |
|
The title of your application, as declared in |
The SpringApplication.setBanner(…) method can be used if you want to generate a banner programmatically.
Use the org.springframework.boot.Banner interface and implement your own printBanner() method.
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You can also use the spring.main.banner-mode property to determine if the banner has to be printed on System.out (console), sent to the configured logger (log), or not produced at all (off).
The printed banner is registered as a singleton bean under the following name: springBootBanner.
|
The To use the |
1.4. Customizing SpringApplication
If the SpringApplication defaults are not to your taste, you can instead create a local instance and customize it.
For example, to turn off the banner, you could write:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApplication.class);
application.setBannerMode(Banner.Mode.OFF);
application.run(args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args) {
setBannerMode(Banner.Mode.OFF)
}
}
The constructor arguments passed to SpringApplication are configuration sources for Spring beans.
In most cases, these are references to @Configuration classes, but they could also be direct references @Component classes.
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It is also possible to configure the SpringApplication by using an application.properties file.
See Externalized Configuration for details.
For a complete list of the configuration options, see the SpringApplication Javadoc.
1.5. Fluent Builder API
If you need to build an ApplicationContext hierarchy (multiple contexts with a parent/child relationship) or if you prefer using a “fluent” builder API, you can use the SpringApplicationBuilder.
The SpringApplicationBuilder lets you chain together multiple method calls and includes parent and child methods that let you create a hierarchy, as shown in the following example:
new SpringApplicationBuilder().sources(Parent.class)
.child(Application.class)
.bannerMode(Banner.Mode.OFF)
.run(args);
SpringApplicationBuilder()
.sources(Parent::class.java)
.child(Application::class.java)
.bannerMode(Banner.Mode.OFF)
.run(*args)
There are some restrictions when creating an ApplicationContext hierarchy.
For example, Web components must be contained within the child context, and the same Environment is used for both parent and child contexts.
See the SpringApplicationBuilder Javadoc for full details.
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1.6. Application Availability
When deployed on platforms, applications can provide information about their availability to the platform using infrastructure such as Kubernetes Probes. Spring Boot includes out-of-the box support for the commonly used “liveness” and “readiness” availability states. If you are using Spring Boot’s “actuator” support then these states are exposed as health endpoint groups.
In addition, you can also obtain availability states by injecting the ApplicationAvailability interface into your own beans.
1.6.1. Liveness State
The “Liveness” state of an application tells whether its internal state allows it to work correctly, or recover by itself if it is currently failing. A broken “Liveness” state means that the application is in a state that it cannot recover from, and the infrastructure should restart the application.
| In general, the "Liveness" state should not be based on external checks, such as Health checks. If it did, a failing external system (a database, a Web API, an external cache) would trigger massive restarts and cascading failures across the platform. |
The internal state of Spring Boot applications is mostly represented by the Spring ApplicationContext.
If the application context has started successfully, Spring Boot assumes that the application is in a valid state.
An application is considered live as soon as the context has been refreshed, see Spring Boot application lifecycle and related Application Events.
1.6.2. Readiness State
The “Readiness” state of an application tells whether the application is ready to handle traffic.
A failing “Readiness” state tells the platform that it should not route traffic to the application for now.
This typically happens during startup, while CommandLineRunner and ApplicationRunner components are being processed, or at any time if the application decides that it is too busy for additional traffic.
An application is considered ready as soon as application and command-line runners have been called, see Spring Boot application lifecycle and related Application Events.
Tasks expected to run during startup should be executed by CommandLineRunner and ApplicationRunner components instead of using Spring component lifecycle callbacks such as @PostConstruct.
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1.6.3. Managing the Application Availability State
Application components can retrieve the current availability state at any time, by injecting the ApplicationAvailability interface and calling methods on it.
More often, applications will want to listen to state updates or update the state of the application.
For example, we can export the "Readiness" state of the application to a file so that a Kubernetes "exec Probe" can look at this file:
@Component
public class MyReadinessStateExporter {
@EventListener
public void onStateChange(AvailabilityChangeEvent<ReadinessState> event) {
switch (event.getState()) {
case ACCEPTING_TRAFFIC -> {
// create file /tmp/healthy
}
case REFUSING_TRAFFIC -> {
// remove file /tmp/healthy
}
}
}
}
@Component
class MyReadinessStateExporter {
@EventListener
fun onStateChange(event: AvailabilityChangeEvent<ReadinessState?>) {
when (event.state) {
ReadinessState.ACCEPTING_TRAFFIC -> {
// create file /tmp/healthy
}
ReadinessState.REFUSING_TRAFFIC -> {
// remove file /tmp/healthy
}
else -> {
// ...
}
}
}
}
We can also update the state of the application, when the application breaks and cannot recover:
@Component
public class MyLocalCacheVerifier {
private final ApplicationEventPublisher eventPublisher;
public MyLocalCacheVerifier(ApplicationEventPublisher eventPublisher) {
this.eventPublisher = eventPublisher;
}
public void checkLocalCache() {
try {
// ...
}
catch (CacheCompletelyBrokenException ex) {
AvailabilityChangeEvent.publish(this.eventPublisher, ex, LivenessState.BROKEN);
}
}
}
@Component
class MyLocalCacheVerifier(private val eventPublisher: ApplicationEventPublisher) {
fun checkLocalCache() {
try {
// ...
} catch (ex: CacheCompletelyBrokenException) {
AvailabilityChangeEvent.publish(eventPublisher, ex, LivenessState.BROKEN)
}
}
}
Spring Boot provides Kubernetes HTTP probes for "Liveness" and "Readiness" with Actuator Health Endpoints. You can get more guidance about deploying Spring Boot applications on Kubernetes in the dedicated section.
1.7. Application Events and Listeners
In addition to the usual Spring Framework events, such as ContextRefreshedEvent, a SpringApplication sends some additional application events.
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Some events are actually triggered before the If you want those listeners to be registered automatically, regardless of the way the application is created, you can add a org.springframework.context.ApplicationListener=com.example.project.MyListener |
Application events are sent in the following order, as your application runs:
-
An
ApplicationStartingEventis sent at the start of a run but before any processing, except for the registration of listeners and initializers. -
An
ApplicationEnvironmentPreparedEventis sent when theEnvironmentto be used in the context is known but before the context is created. -
An
ApplicationContextInitializedEventis sent when theApplicationContextis prepared and ApplicationContextInitializers have been called but before any bean definitions are loaded. -
An
ApplicationPreparedEventis sent just before the refresh is started but after bean definitions have been loaded. -
An
ApplicationStartedEventis sent after the context has been refreshed but before any application and command-line runners have been called. -
An
AvailabilityChangeEventis sent right after withLivenessState.CORRECTto indicate that the application is considered as live. -
An
ApplicationReadyEventis sent after any application and command-line runners have been called. -
An
AvailabilityChangeEventis sent right after withReadinessState.ACCEPTING_TRAFFICto indicate that the application is ready to service requests. -
An
ApplicationFailedEventis sent if there is an exception on startup.
The above list only includes SpringApplicationEvents that are tied to a SpringApplication.
In addition to these, the following events are also published after ApplicationPreparedEvent and before ApplicationStartedEvent:
-
A
WebServerInitializedEventis sent after theWebServeris ready.ServletWebServerInitializedEventandReactiveWebServerInitializedEventare the servlet and reactive variants respectively. -
A
ContextRefreshedEventis sent when anApplicationContextis refreshed.
| You often need not use application events, but it can be handy to know that they exist. Internally, Spring Boot uses events to handle a variety of tasks. |
| Event listeners should not run potentially lengthy tasks as they execute in the same thread by default. Consider using application and command-line runners instead. |
Application events are sent by using Spring Framework’s event publishing mechanism.
Part of this mechanism ensures that an event published to the listeners in a child context is also published to the listeners in any ancestor contexts.
As a result of this, if your application uses a hierarchy of SpringApplication instances, a listener may receive multiple instances of the same type of application event.
To allow your listener to distinguish between an event for its context and an event for a descendant context, it should request that its application context is injected and then compare the injected context with the context of the event.
The context can be injected by implementing ApplicationContextAware or, if the listener is a bean, by using @Autowired.
1.8. Web Environment
A SpringApplication attempts to create the right type of ApplicationContext on your behalf.
The algorithm used to determine a WebApplicationType is the following:
-
If Spring MVC is present, an
AnnotationConfigServletWebServerApplicationContextis used -
If Spring MVC is not present and Spring WebFlux is present, an
AnnotationConfigReactiveWebServerApplicationContextis used -
Otherwise,
AnnotationConfigApplicationContextis used
This means that if you are using Spring MVC and the new WebClient from Spring WebFlux in the same application, Spring MVC will be used by default.
You can override that easily by calling setWebApplicationType(WebApplicationType).
It is also possible to take complete control of the ApplicationContext type that is used by calling setApplicationContextFactory(…).
It is often desirable to call setWebApplicationType(WebApplicationType.NONE) when using SpringApplication within a JUnit test.
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1.9. Accessing Application Arguments
If you need to access the application arguments that were passed to SpringApplication.run(…), you can inject a org.springframework.boot.ApplicationArguments bean.
The ApplicationArguments interface provides access to both the raw String[] arguments as well as parsed option and non-option arguments, as shown in the following example:
@Component
public class MyBean {
public MyBean(ApplicationArguments args) {
boolean debug = args.containsOption("debug");
List<String> files = args.getNonOptionArgs();
if (debug) {
System.out.println(files);
}
// if run with "--debug logfile.txt" prints ["logfile.txt"]
}
}
@Component
class MyBean(args: ApplicationArguments) {
init {
val debug = args.containsOption("debug")
val files = args.nonOptionArgs
if (debug) {
println(files)
}
// if run with "--debug logfile.txt" prints ["logfile.txt"]
}
}
Spring Boot also registers a CommandLinePropertySource with the Spring Environment.
This lets you also inject single application arguments by using the @Value annotation.
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1.10. Using the ApplicationRunner or CommandLineRunner
If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces.
Both interfaces work in the same way and offer a single run method, which is called just before SpringApplication.run(…) completes.
| This contract is well suited for tasks that should run after application startup but before it starts accepting traffic. |
The CommandLineRunner interfaces provides access to application arguments as a string array, whereas the ApplicationRunner uses the ApplicationArguments interface discussed earlier.
The following example shows a CommandLineRunner with a run method:
@Component
public class MyCommandLineRunner implements CommandLineRunner {
@Override
public void run(String... args) {
// Do something...
}
}
@Component
class MyCommandLineRunner : CommandLineRunner {
override fun run(vararg args: String) {
// Do something...
}
}
If several CommandLineRunner or ApplicationRunner beans are defined that must be called in a specific order, you can additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation.
1.11. Application Exit
Each SpringApplication registers a shutdown hook with the JVM to ensure that the ApplicationContext closes gracefully on exit.
All the standard Spring lifecycle callbacks (such as the DisposableBean interface or the @PreDestroy annotation) can be used.
In addition, beans may implement the org.springframework.boot.ExitCodeGenerator interface if they wish to return a specific exit code when SpringApplication.exit() is called.
This exit code can then be passed to System.exit() to return it as a status code, as shown in the following example:
@SpringBootApplication
public class MyApplication {
@Bean
public ExitCodeGenerator exitCodeGenerator() {
return () -> 42;
}
public static void main(String[] args) {
System.exit(SpringApplication.exit(SpringApplication.run(MyApplication.class, args)));
}
}
@SpringBootApplication
class MyApplication {
@Bean
fun exitCodeGenerator() = ExitCodeGenerator { 42 }
}
fun main(args: Array<String>) {
exitProcess(SpringApplication.exit(
runApplication<MyApplication>(*args)))
}
Also, the ExitCodeGenerator interface may be implemented by exceptions.
When such an exception is encountered, Spring Boot returns the exit code provided by the implemented getExitCode() method.
If there is more than one ExitCodeGenerator, the first non-zero exit code that is generated is used.
To control the order in which the generators are called, additionally implement the org.springframework.core.Ordered interface or use the org.springframework.core.annotation.Order annotation.
1.12. Admin Features
It is possible to enable admin-related features for the application by specifying the spring.application.admin.enabled property.
This exposes the SpringApplicationAdminMXBean on the platform MBeanServer.
You could use this feature to administer your Spring Boot application remotely.
This feature could also be useful for any service wrapper implementation.
If you want to know on which HTTP port the application is running, get the property with a key of local.server.port.
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1.13. Application Startup tracking
During the application startup, the SpringApplication and the ApplicationContext perform many tasks related to the application lifecycle,
the beans lifecycle or even processing application events.
With ApplicationStartup, Spring Framework allows you to track the application startup sequence with StartupStep objects.
This data can be collected for profiling purposes, or just to have a better understanding of an application startup process.
You can choose an ApplicationStartup implementation when setting up the SpringApplication instance.
For example, to use the BufferingApplicationStartup, you could write:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApplication.class);
application.setApplicationStartup(new BufferingApplicationStartup(2048));
application.run(args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args) {
applicationStartup = BufferingApplicationStartup(2048)
}
}
The first available implementation, FlightRecorderApplicationStartup is provided by Spring Framework.
It adds Spring-specific startup events to a Java Flight Recorder session and is meant for profiling applications and correlating their Spring context lifecycle with JVM events (such as allocations, GCs, class loading…).
Once configured, you can record data by running the application with the Flight Recorder enabled:
$ java -XX:StartFlightRecording:filename=recording.jfr,duration=10s -jar demo.jarSpring Boot ships with the BufferingApplicationStartup variant; this implementation is meant for buffering the startup steps and draining them into an external metrics system.
Applications can ask for the bean of type BufferingApplicationStartup in any component.
Spring Boot can also be configured to expose a startup endpoint that provides this information as a JSON document.
1.14. Virtual threads
If you’re running on Java 21 or up, you can enable virtual threads by setting the property spring.threads.virtual.enabled to true.
Before turning on this option for your application, you should consider reading the official Java virtual threads documentation.
In some cases, applications can experience lower throughput because of "Pinned Virtual Threads"; this page also explains how to detect such cases with JDK Flight Recorder or the jcmd CLI.
| If virtual threads are enabled, properties which configure thread pools don’t have an effect anymore. That’s because virtual threads are scheduled on a JVM wide platform thread pool and not on dedicated thread pools. |
One side effect of virtual threads is that they are daemon threads.
A JVM will exit if all of its threads are daemon threads.
This behavior can be a problem when you rely on @Scheduled beans, for example, to keep your application alive.
If you use virtual threads, the scheduler thread is a virtual thread and therefore a daemon thread and won’t keep the JVM alive.
This not only affects scheduling and can be the case with other technologies too.
To keep the JVM running in all cases, it is recommended to set the property spring.main.keep-alive to true.
This ensures that the JVM is kept alive, even if all threads are virtual threads.
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2. Externalized Configuration
Spring Boot lets you externalize your configuration so that you can work with the same application code in different environments. You can use a variety of external configuration sources including Java properties files, YAML files, environment variables, and command-line arguments.
Property values can be injected directly into your beans by using the @Value annotation, accessed through Spring’s Environment abstraction, or be bound to structured objects through @ConfigurationProperties.
Spring Boot uses a very particular PropertySource order that is designed to allow sensible overriding of values.
Later property sources can override the values defined in earlier ones.
Sources are considered in the following order:
-
Default properties (specified by setting
SpringApplication.setDefaultProperties). -
@PropertySourceannotations on your@Configurationclasses. Please note that such property sources are not added to theEnvironmentuntil the application context is being refreshed. This is too late to configure certain properties such aslogging.*andspring.main.*which are read before refresh begins. -
Config data (such as
application.propertiesfiles). -
A
RandomValuePropertySourcethat has properties only inrandom.*. -
OS environment variables.
-
Java System properties (
System.getProperties()). -
JNDI attributes from
java:comp/env. -
ServletContextinit parameters. -
ServletConfiginit parameters. -
Properties from
SPRING_APPLICATION_JSON(inline JSON embedded in an environment variable or system property). -
Command line arguments.
-
propertiesattribute on your tests. Available on@SpringBootTestand the test annotations for testing a particular slice of your application. -
@DynamicPropertySourceannotations in your tests. -
@TestPropertySourceannotations on your tests. -
Devtools global settings properties in the
$HOME/.config/spring-bootdirectory when devtools is active.
Config data files are considered in the following order:
-
Application properties packaged inside your jar (
application.propertiesand YAML variants). -
Profile-specific application properties packaged inside your jar (
application-{profile}.propertiesand YAML variants). -
Application properties outside of your packaged jar (
application.propertiesand YAML variants). -
Profile-specific application properties outside of your packaged jar (
application-{profile}.propertiesand YAML variants).
It is recommended to stick with one format for your entire application.
If you have configuration files with both .properties and YAML format in the same location, .properties takes precedence.
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If you use environment variables rather than system properties, most operating systems disallow period-separated key names, but you can use underscores instead (for example, SPRING_CONFIG_NAME instead of spring.config.name).
See Binding From Environment Variables for details.
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If your application runs in a servlet container or application server, then JNDI properties (in java:comp/env) or servlet context initialization parameters can be used instead of, or as well as, environment variables or system properties.
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To provide a concrete example, suppose you develop a @Component that uses a name property, as shown in the following example:
@Component
public class MyBean {
@Value("${name}")
private String name;
// ...
}
@Component
class MyBean {
@Value("\${name}")
private val name: String? = null
// ...
}
On your application classpath (for example, inside your jar) you can have an application.properties file that provides a sensible default property value for name.
When running in a new environment, an application.properties file can be provided outside of your jar that overrides the name.
For one-off testing, you can launch with a specific command line switch (for example, java -jar app.jar --name="Spring").
The env and configprops endpoints can be useful in determining why a property has a particular value.
You can use these two endpoints to diagnose unexpected property values.
See the "Production ready features" section for details.
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2.1. Accessing Command Line Properties
By default, SpringApplication converts any command line option arguments (that is, arguments starting with --, such as --server.port=9000) to a property and adds them to the Spring Environment.
As mentioned previously, command line properties always take precedence over file-based property sources.
If you do not want command line properties to be added to the Environment, you can disable them by using SpringApplication.setAddCommandLineProperties(false).
2.2. JSON Application Properties
Environment variables and system properties often have restrictions that mean some property names cannot be used. To help with this, Spring Boot allows you to encode a block of properties into a single JSON structure.
When your application starts, any spring.application.json or SPRING_APPLICATION_JSON properties will be parsed and added to the Environment.
For example, the SPRING_APPLICATION_JSON property can be supplied on the command line in a UN*X shell as an environment variable:
$ SPRING_APPLICATION_JSON='{"my":{"name":"test"}}' java -jar myapp.jarIn the preceding example, you end up with my.name=test in the Spring Environment.
The same JSON can also be provided as a system property:
$ java -Dspring.application.json='{"my":{"name":"test"}}' -jar myapp.jarOr you could supply the JSON by using a command line argument:
$ java -jar myapp.jar --spring.application.json='{"my":{"name":"test"}}'If you are deploying to a classic Application Server, you could also use a JNDI variable named java:comp/env/spring.application.json.
Although null values from the JSON will be added to the resulting property source, the PropertySourcesPropertyResolver treats null properties as missing values.
This means that the JSON cannot override properties from lower order property sources with a null value.
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2.3. External Application Properties
Spring Boot will automatically find and load application.properties and application.yaml files from the following locations when your application starts:
-
From the classpath
-
The classpath root
-
The classpath
/configpackage
-
-
From the current directory
-
The current directory
-
The
config/subdirectory in the current directory -
Immediate child directories of the
config/subdirectory
-
The list is ordered by precedence (with values from lower items overriding earlier ones).
Documents from the loaded files are added as PropertySources to the Spring Environment.
If you do not like application as the configuration file name, you can switch to another file name by specifying a spring.config.name environment property.
For example, to look for myproject.properties and myproject.yaml files you can run your application as follows:
$ java -jar myproject.jar --spring.config.name=myprojectYou can also refer to an explicit location by using the spring.config.location environment property.
This property accepts a comma-separated list of one or more locations to check.
The following example shows how to specify two distinct files:
$ java -jar myproject.jar --spring.config.location=\
optional:classpath:/default.properties,\
optional:classpath:/override.properties
Use the prefix optional: if the locations are optional and you do not mind if they do not exist.
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spring.config.name, spring.config.location, and spring.config.additional-location are used very early to determine which files have to be loaded.
They must be defined as an environment property (typically an OS environment variable, a system property, or a command-line argument).
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If spring.config.location contains directories (as opposed to files), they should end in /.
At runtime they will be appended with the names generated from spring.config.name before being loaded.
Files specified in spring.config.location are imported directly.
Both directory and file location values are also expanded to check for profile-specific files.
For example, if you have a spring.config.location of classpath:myconfig.properties, you will also find appropriate classpath:myconfig-<profile>.properties files are loaded.
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In most situations, each spring.config.location item you add will reference a single file or directory.
Locations are processed in the order that they are defined and later ones can override the values of earlier ones.
If you have a complex location setup, and you use profile-specific configuration files, you may need to provide further hints so that Spring Boot knows how they should be grouped.
A location group is a collection of locations that are all considered at the same level.
For example, you might want to group all classpath locations, then all external locations.
Items within a location group should be separated with ;.
See the example in the “Profile Specific Files” section for more details.
Locations configured by using spring.config.location replace the default locations.
For example, if spring.config.location is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/, the complete set of locations considered is:
-
optional:classpath:custom-config/ -
optional:file:./custom-config/
If you prefer to add additional locations, rather than replacing them, you can use spring.config.additional-location.
Properties loaded from additional locations can override those in the default locations.
For example, if spring.config.additional-location is configured with the value optional:classpath:/custom-config/,optional:file:./custom-config/, the complete set of locations considered is:
-
optional:classpath:/;optional:classpath:/config/ -
optional:file:./;optional:file:./config/;optional:file:./config/*/ -
optional:classpath:custom-config/ -
optional:file:./custom-config/
This search ordering lets you specify default values in one configuration file and then selectively override those values in another.
You can provide default values for your application in application.properties (or whatever other basename you choose with spring.config.name) in one of the default locations.
These default values can then be overridden at runtime with a different file located in one of the custom locations.
2.3.1. Optional Locations
By default, when a specified config data location does not exist, Spring Boot will throw a ConfigDataLocationNotFoundException and your application will not start.
If you want to specify a location, but you do not mind if it does not always exist, you can use the optional: prefix.
You can use this prefix with the spring.config.location and spring.config.additional-location properties, as well as with spring.config.import declarations.
For example, a spring.config.import value of optional:file:./myconfig.properties allows your application to start, even if the myconfig.properties file is missing.
If you want to ignore all ConfigDataLocationNotFoundExceptions and always continue to start your application, you can use the spring.config.on-not-found property.
Set the value to ignore using SpringApplication.setDefaultProperties(…) or with a system/environment variable.
2.3.2. Wildcard Locations
If a config file location includes the * character for the last path segment, it is considered a wildcard location.
Wildcards are expanded when the config is loaded so that immediate subdirectories are also checked.
Wildcard locations are particularly useful in an environment such as Kubernetes when there are multiple sources of config properties.
For example, if you have some Redis configuration and some MySQL configuration, you might want to keep those two pieces of configuration separate, while requiring that both those are present in an application.properties file.
This might result in two separate application.properties files mounted at different locations such as /config/redis/application.properties and /config/mysql/application.properties.
In such a case, having a wildcard location of config/*/, will result in both files being processed.
By default, Spring Boot includes config/*/ in the default search locations.
It means that all subdirectories of the /config directory outside of your jar will be searched.
You can use wildcard locations yourself with the spring.config.location and spring.config.additional-location properties.
A wildcard location must contain only one * and end with */ for search locations that are directories or */<filename> for search locations that are files.
Locations with wildcards are sorted alphabetically based on the absolute path of the file names.
|
Wildcard locations only work with external directories.
You cannot use a wildcard in a classpath: location.
|
2.3.3. Profile Specific Files
As well as application property files, Spring Boot will also attempt to load profile-specific files using the naming convention application-{profile}.
For example, if your application activates a profile named prod and uses YAML files, then both application.yaml and application-prod.yaml will be considered.
Profile-specific properties are loaded from the same locations as standard application.properties, with profile-specific files always overriding the non-specific ones.
If several profiles are specified, a last-wins strategy applies.
For example, if profiles prod,live are specified by the spring.profiles.active property, values in application-prod.properties can be overridden by those in application-live.properties.
|
The last-wins strategy applies at the location group level.
A For example, continuing our /cfg application-live.properties /ext application-live.properties application-prod.properties When we have a
When we have
|
The Environment has a set of default profiles (by default, [default]) that are used if no active profiles are set.
In other words, if no profiles are explicitly activated, then properties from application-default are considered.
| Properties files are only ever loaded once. If you have already directly imported a profile specific property files then it will not be imported a second time. |
2.3.4. Importing Additional Data
Application properties may import further config data from other locations using the spring.config.import property.
Imports are processed as they are discovered, and are treated as additional documents inserted immediately below the one that declares the import.
For example, you might have the following in your classpath application.properties file:
spring.application.name=myapp
spring.config.import=optional:file:./dev.propertiesspring:
application:
name: "myapp"
config:
import: "optional:file:./dev.properties"This will trigger the import of a dev.properties file in current directory (if such a file exists).
Values from the imported dev.properties will take precedence over the file that triggered the import.
In the above example, the dev.properties could redefine spring.application.name to a different value.
An import will only be imported once no matter how many times it is declared. The order an import is defined inside a single document within the properties/yaml file does not matter. For instance, the two examples below produce the same result:
spring.config.import=my.properties
my.property=valuespring:
config:
import: "my.properties"
my:
property: "value"my.property=value
spring.config.import=my.propertiesmy:
property: "value"
spring:
config:
import: "my.properties"In both of the above examples, the values from the my.properties file will take precedence over the file that triggered its import.
Several locations can be specified under a single spring.config.import key.
Locations will be processed in the order that they are defined, with later imports taking precedence.
When appropriate, Profile-specific variants are also considered for import.
The example above would import both my.properties as well as any my-<profile>.properties variants.
|
|
Spring Boot includes pluggable API that allows various different location addresses to be supported. By default you can import Java Properties, YAML and “configuration trees”. Third-party jars can offer support for additional technologies (there is no requirement for files to be local). For example, you can imagine config data being from external stores such as Consul, Apache ZooKeeper or Netflix Archaius. If you want to support your own locations, see the |
2.3.5. Importing Extensionless Files
Some cloud platforms cannot add a file extension to volume mounted files. To import these extensionless files, you need to give Spring Boot a hint so that it knows how to load them. You can do this by putting an extension hint in square brackets.
For example, suppose you have a /etc/config/myconfig file that you wish to import as yaml.
You can import it from your application.properties using the following:
spring.config.import=file:/etc/config/myconfig[.yaml]spring:
config:
import: "file:/etc/config/myconfig[.yaml]"2.3.6. Using Configuration Trees
When running applications on a cloud platform (such as Kubernetes) you often need to read config values that the platform supplies. It is not uncommon to use environment variables for such purposes, but this can have drawbacks, especially if the value is supposed to be kept secret.
As an alternative to environment variables, many cloud platforms now allow you to map configuration into mounted data volumes.
For example, Kubernetes can volume mount both ConfigMaps and Secrets.
There are two common volume mount patterns that can be used:
-
A single file contains a complete set of properties (usually written as YAML).
-
Multiple files are written to a directory tree, with the filename becoming the ‘key’ and the contents becoming the ‘value’.
For the first case, you can import the YAML or Properties file directly using spring.config.import as described above.
For the second case, you need to use the configtree: prefix so that Spring Boot knows it needs to expose all the files as properties.
As an example, let’s imagine that Kubernetes has mounted the following volume:
etc/
config/
myapp/
username
password
The contents of the username file would be a config value, and the contents of password would be a secret.
To import these properties, you can add the following to your application.properties or application.yaml file:
spring.config.import=optional:configtree:/etc/config/spring:
config:
import: "optional:configtree:/etc/config/"You can then access or inject myapp.username and myapp.password properties from the Environment in the usual way.
The names of the folders and files under the config tree form the property name.
In the above example, to access the properties as username and password, you can set spring.config.import to optional:configtree:/etc/config/myapp.
|
Filenames with dot notation are also correctly mapped.
For example, in the above example, a file named myapp.username in /etc/config would result in a myapp.username property in the Environment.
|
Configuration tree values can be bound to both string String and byte[] types depending on the contents expected.
|
If you have multiple config trees to import from the same parent folder you can use a wildcard shortcut.
Any configtree: location that ends with /*/ will import all immediate children as config trees.
As with a non-wildcard import, the names of the folders and files under each config tree form the property name.
For example, given the following volume:
etc/
config/
dbconfig/
db/
username
password
mqconfig/
mq/
username
password
You can use configtree:/etc/config/*/ as the import location:
spring.config.import=optional:configtree:/etc/config/*/spring:
config:
import: "optional:configtree:/etc/config/*/"This will add db.username, db.password, mq.username and mq.password properties.
| Directories loaded using a wildcard are sorted alphabetically. If you need a different order, then you should list each location as a separate import |
Configuration trees can also be used for Docker secrets.
When a Docker swarm service is granted access to a secret, the secret gets mounted into the container.
For example, if a secret named db.password is mounted at location /run/secrets/, you can make db.password available to the Spring environment using the following:
spring.config.import=optional:configtree:/run/secrets/spring:
config:
import: "optional:configtree:/run/secrets/"2.3.7. Property Placeholders
The values in application.properties and application.yaml are filtered through the existing Environment when they are used, so you can refer back to previously defined values (for example, from System properties or environment variables).
The standard ${name} property-placeholder syntax can be used anywhere within a value.
Property placeholders can also specify a default value using a : to separate the default value from the property name, for example ${name:default}.
The use of placeholders with and without defaults is shown in the following example:
app.name=MyApp
app.description=${app.name} is a Spring Boot application written by ${username:Unknown}app:
name: "MyApp"
description: "${app.name} is a Spring Boot application written by ${username:Unknown}"Assuming that the username property has not been set elsewhere, app.description will have the value MyApp is a Spring Boot application written by Unknown.
|
You should always refer to property names in the placeholder using their canonical form (kebab-case using only lowercase letters).
This will allow Spring Boot to use the same logic as it does when relaxed binding For example, |
| You can also use this technique to create “short” variants of existing Spring Boot properties. See the howto.html how-to for details. |
2.3.8. Working With Multi-Document Files
Spring Boot allows you to split a single physical file into multiple logical documents which are each added independently. Documents are processed in order, from top to bottom. Later documents can override the properties defined in earlier ones.
For application.yaml files, the standard YAML multi-document syntax is used.
Three consecutive hyphens represent the end of one document, and the start of the next.
For example, the following file has two logical documents:
spring:
application:
name: "MyApp"
---
spring:
application:
name: "MyCloudApp"
config:
activate:
on-cloud-platform: "kubernetes"For application.properties files a special #--- or !--- comment is used to mark the document splits:
spring.application.name=MyApp
#---
spring.application.name=MyCloudApp
spring.config.activate.on-cloud-platform=kubernetes| Property file separators must not have any leading whitespace and must have exactly three hyphen characters. The lines immediately before and after the separator must not be same comment prefix. |
Multi-document property files are often used in conjunction with activation properties such as spring.config.activate.on-profile.
See the next section for details.
|
Multi-document property files cannot be loaded by using the @PropertySource or @TestPropertySource annotations.
|
2.3.9. Activation Properties
It is sometimes useful to only activate a given set of properties when certain conditions are met. For example, you might have properties that are only relevant when a specific profile is active.
You can conditionally activate a properties document using spring.config.activate.*.
The following activation properties are available:
| Property | Note |
|---|---|
|
A profile expression that must match for the document to be active. |
|
The |
For example, the following specifies that the second document is only active when running on Kubernetes, and only when either the “prod” or “staging” profiles are active:
myprop=always-set
#---
spring.config.activate.on-cloud-platform=kubernetes
spring.config.activate.on-profile=prod | staging
myotherprop=sometimes-setmyprop:
"always-set"
---
spring:
config:
activate:
on-cloud-platform: "kubernetes"
on-profile: "prod | staging"
myotherprop: "sometimes-set"2.4. Encrypting Properties
Spring Boot does not provide any built-in support for encrypting property values, however, it does provide the hook points necessary to modify values contained in the Spring Environment.
The EnvironmentPostProcessor interface allows you to manipulate the Environment before the application starts.
See howto.html for details.
If you need a secure way to store credentials and passwords, the Spring Cloud Vault project provides support for storing externalized configuration in HashiCorp Vault.
2.5. Working With YAML
YAML is a superset of JSON and, as such, is a convenient format for specifying hierarchical configuration data.
The SpringApplication class automatically supports YAML as an alternative to properties whenever you have the SnakeYAML library on your classpath.
If you use “Starters”, SnakeYAML is automatically provided by spring-boot-starter.
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2.5.1. Mapping YAML to Properties
YAML documents need to be converted from their hierarchical format to a flat structure that can be used with the Spring Environment.
For example, consider the following YAML document:
environments:
dev:
url: "https://dev.example.com"
name: "Developer Setup"
prod:
url: "https://another.example.com"
name: "My Cool App"In order to access these properties from the Environment, they would be flattened as follows:
environments.dev.url=https://dev.example.com
environments.dev.name=Developer Setup
environments.prod.url=https://another.example.com
environments.prod.name=My Cool AppLikewise, YAML lists also need to be flattened.
They are represented as property keys with [index] dereferencers.
For example, consider the following YAML:
my:
servers:
- "dev.example.com"
- "another.example.com"The preceding example would be transformed into these properties:
my.servers[0]=dev.example.com
my.servers[1]=another.example.com
Properties that use the [index] notation can be bound to Java List or Set objects using Spring Boot’s Binder class.
For more details see the “Type-safe Configuration Properties” section below.
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YAML files cannot be loaded by using the @PropertySource or @TestPropertySource annotations.
So, in the case that you need to load values that way, you need to use a properties file.
|
2.5.2. Directly Loading YAML
Spring Framework provides two convenient classes that can be used to load YAML documents.
The YamlPropertiesFactoryBean loads YAML as Properties and the YamlMapFactoryBean loads YAML as a Map.
You can also use the YamlPropertySourceLoader class if you want to load YAML as a Spring PropertySource.
2.6. Configuring Random Values
The RandomValuePropertySource is useful for injecting random values (for example, into secrets or test cases).
It can produce integers, longs, uuids, or strings, as shown in the following example:
my.secret=${random.value}
my.number=${random.int}
my.bignumber=${random.long}
my.uuid=${random.uuid}
my.number-less-than-ten=${random.int(10)}
my.number-in-range=${random.int[1024,65536]}my:
secret: "${random.value}"
number: "${random.int}"
bignumber: "${random.long}"
uuid: "${random.uuid}"
number-less-than-ten: "${random.int(10)}"
number-in-range: "${random.int[1024,65536]}"The random.int* syntax is OPEN value (,max) CLOSE where the OPEN,CLOSE are any character and value,max are integers.
If max is provided, then value is the minimum value and max is the maximum value (exclusive).
2.7. Configuring System Environment Properties
Spring Boot supports setting a prefix for environment properties.
This is useful if the system environment is shared by multiple Spring Boot applications with different configuration requirements.
The prefix for system environment properties can be set directly on SpringApplication.
For example, if you set the prefix to input, a property such as remote.timeout will also be resolved as input.remote.timeout in the system environment.
2.8. Type-safe Configuration Properties
Using the @Value("${property}") annotation to inject configuration properties can sometimes be cumbersome, especially if you are working with multiple properties or your data is hierarchical in nature.
Spring Boot provides an alternative method of working with properties that lets strongly typed beans govern and validate the configuration of your application.
2.8.1. JavaBean Properties Binding
It is possible to bind a bean declaring standard JavaBean properties as shown in the following example:
@ConfigurationProperties("my.service")
public class MyProperties {
private boolean enabled;
private InetAddress remoteAddress;
private final Security security = new Security();
public static class Security {
private String username;
private String password;
private List<String> roles = new ArrayList<>(Collections.singleton("USER"));
}
}
@ConfigurationProperties("my.service")
class MyProperties {
var isEnabled = false
var remoteAddress: InetAddress? = null
val security = Security()
class Security {
var username: String? = null
var password: String? = null
var roles: List<String> = ArrayList(setOf("USER"))
}
}
The preceding POJO defines the following properties:
-
my.service.enabled, with a value offalseby default. -
my.service.remote-address, with a type that can be coerced fromString. -
my.service.security.username, with a nested "security" object whose name is determined by the name of the property. In particular, the type is not used at all there and could have beenSecurityProperties. -
my.service.security.password. -
my.service.security.roles, with a collection ofStringthat defaults toUSER.
The properties that map to @ConfigurationProperties classes available in Spring Boot, which are configured through properties files, YAML files, environment variables, and other mechanisms, are public API but the accessors (getters/setters) of the class itself are not meant to be used directly.
|
|
Such arrangement relies on a default empty constructor and getters and setters are usually mandatory, since binding is through standard Java Beans property descriptors, just like in Spring MVC. A setter may be omitted in the following cases:
Some people use Project Lombok to add getters and setters automatically. Make sure that Lombok does not generate any particular constructor for such a type, as it is used automatically by the container to instantiate the object. Finally, only standard Java Bean properties are considered and binding on static properties is not supported. |
2.8.2. Constructor Binding
The example in the previous section can be rewritten in an immutable fashion as shown in the following example:
@ConfigurationProperties("my.service")
public class MyProperties {
public MyProperties(boolean enabled, InetAddress remoteAddress, Security security) {
this.enabled = enabled;
this.remoteAddress = remoteAddress;
this.security = security;
}
public static class Security {
public Security(String username, String password, @DefaultValue("USER") List<String> roles) {
this.username = username;
this.password = password;
this.roles = roles;
}
}
}
@ConfigurationProperties("my.service")
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
val security: Security) {
class Security(val username: String, val password: String,
@param:DefaultValue("USER") val roles: List<String>)
}
In this setup, the presence of a single parameterized constructor implies that constructor binding should be used.
This means that the binder will find a constructor with the parameters that you wish to have bound.
If your class has multiple constructors, the @ConstructorBinding annotation can be used to specify which constructor to use for constructor binding.
To opt out of constructor binding for a class with a single parameterized constructor, the constructor must be annotated with @Autowired or made private.
Constructor binding can be used with records.
Unless your record has multiple constructors, there is no need to use @ConstructorBinding.
Nested members of a constructor bound class (such as Security in the example above) will also be bound through their constructor.
Default values can be specified using @DefaultValue on constructor parameters and record components.
The conversion service will be applied to coerce the annotation’s String value to the target type of a missing property.
Referring to the previous example, if no properties are bound to Security, the MyProperties instance will contain a null value for security.
To make it contain a non-null instance of Security even when no properties are bound to it (when using Kotlin, this will require the username and password parameters of Security to be declared as nullable as they do not have default values), use an empty @DefaultValue annotation:
public MyProperties(boolean enabled, InetAddress remoteAddress, @DefaultValue Security security) {
this.enabled = enabled;
this.remoteAddress = remoteAddress;
this.security = security;
}
class MyProperties(val enabled: Boolean, val remoteAddress: InetAddress,
@DefaultValue val security: Security) {
class Security(val username: String?, val password: String?,
@param:DefaultValue("USER") val roles: List<String>)
}
To use constructor binding the class must be enabled using @EnableConfigurationProperties or configuration property scanning.
You cannot use constructor binding with beans that are created by the regular Spring mechanisms (for example @Component beans, beans created by using @Bean methods or beans loaded by using @Import)
|
To use constructor binding the class must be compiled with -parameters.
This will happen automatically if you use Spring Boot’s Gradle plugin or if you use Maven and spring-boot-starter-parent.
|
The use of java.util.Optional with @ConfigurationProperties is not recommended as it is primarily intended for use as a return type.
As such, it is not well-suited to configuration property injection.
For consistency with properties of other types, if you do declare an Optional property and it has no value, null rather than an empty Optional will be bound.
|
To use a reserved keyword in the name of a property, such as my.service.import, use the @Name annotation on the constructor parameter.
|
2.8.3. Enabling @ConfigurationProperties-annotated Types
Spring Boot provides infrastructure to bind @ConfigurationProperties types and register them as beans.
You can either enable configuration properties on a class-by-class basis or enable configuration property scanning that works in a similar manner to component scanning.
Sometimes, classes annotated with @ConfigurationProperties might not be suitable for scanning, for example, if you’re developing your own auto-configuration or you want to enable them conditionally.
In these cases, specify the list of types to process using the @EnableConfigurationProperties annotation.
This can be done on any @Configuration class, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties.class)
public class MyConfiguration {
}
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(SomeProperties::class)
class MyConfiguration
@ConfigurationProperties("some.properties")
public class SomeProperties {
}
@ConfigurationProperties("some.properties")
class SomeProperties
To use configuration property scanning, add the @ConfigurationPropertiesScan annotation to your application.
Typically, it is added to the main application class that is annotated with @SpringBootApplication but it can be added to any @Configuration class.
By default, scanning will occur from the package of the class that declares the annotation.
If you want to define specific packages to scan, you can do so as shown in the following example:
@SpringBootApplication
@ConfigurationPropertiesScan({ "com.example.app", "com.example.another" })
public class MyApplication {
}
@SpringBootApplication
@ConfigurationPropertiesScan("com.example.app", "com.example.another")
class MyApplication
|
When the Assuming that it is in the |
We recommend that @ConfigurationProperties only deal with the environment and, in particular, does not inject other beans from the context.
For corner cases, setter injection can be used or any of the *Aware interfaces provided by the framework (such as EnvironmentAware if you need access to the Environment).
If you still want to inject other beans using the constructor, the configuration properties bean must be annotated with @Component and use JavaBean-based property binding.
2.8.4. Using @ConfigurationProperties-annotated Types
This style of configuration works particularly well with the SpringApplication external YAML configuration, as shown in the following example:
my:
service:
remote-address: 192.168.1.1
security:
username: "admin"
roles:
- "USER"
- "ADMIN"To work with @ConfigurationProperties beans, you can inject them in the same way as any other bean, as shown in the following example:
@Service
public class MyService {
private final MyProperties properties;
public MyService(MyProperties properties) {
this.properties = properties;
}
public void openConnection() {
Server server = new Server(this.properties.getRemoteAddress());
server.start();
// ...
}
// ...
}
@Service
class MyService(val properties: MyProperties) {
fun openConnection() {
val server = Server(properties.remoteAddress)
server.start()
// ...
}
// ...
}
Using @ConfigurationProperties also lets you generate metadata files that can be used by IDEs to offer auto-completion for your own keys.
See the appendix for details.
|
2.8.5. Third-party Configuration
As well as using @ConfigurationProperties to annotate a class, you can also use it on public @Bean methods.
Doing so can be particularly useful when you want to bind properties to third-party components that are outside of your control.
To configure a bean from the Environment properties, add @ConfigurationProperties to its bean registration, as shown in the following example:
@Configuration(proxyBeanMethods = false)
public class ThirdPartyConfiguration {
@Bean
@ConfigurationProperties(prefix = "another")
public AnotherComponent anotherComponent() {
return new AnotherComponent();
}
}
@Configuration(proxyBeanMethods = false)
class ThirdPartyConfiguration {
@Bean
@ConfigurationProperties(prefix = "another")
fun anotherComponent(): AnotherComponent = AnotherComponent()
}
Any JavaBean property defined with the another prefix is mapped onto that AnotherComponent bean in manner similar to the preceding SomeProperties example.
2.8.6. Relaxed Binding
Spring Boot uses some relaxed rules for binding Environment properties to @ConfigurationProperties beans, so there does not need to be an exact match between the Environment property name and the bean property name.
Common examples where this is useful include dash-separated environment properties (for example, context-path binds to contextPath), and capitalized environment properties (for example, PORT binds to port).
As an example, consider the following @ConfigurationProperties class:
@ConfigurationProperties(prefix = "my.main-project.person")
public class MyPersonProperties {
private String firstName;
public String getFirstName() {
return this.firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
}
@ConfigurationProperties(prefix = "my.main-project.person")
class MyPersonProperties {
var firstName: String? = null
}
With the preceding code, the following properties names can all be used:
| Property | Note |
|---|---|
|
Kebab case, which is recommended for use in |
|
Standard camel case syntax. |
|
Underscore notation, which is an alternative format for use in |
|
Upper case format, which is recommended when using system environment variables. |
The prefix value for the annotation must be in kebab case (lowercase and separated by -, such as my.main-project.person).
|
| Property Source | Simple | List |
|---|---|---|
Properties Files |
Camel case, kebab case, or underscore notation |
Standard list syntax using |
YAML Files |
Camel case, kebab case, or underscore notation |
Standard YAML list syntax or comma-separated values |
Environment Variables |
Upper case format with underscore as the delimiter (see Binding From Environment Variables). |
Numeric values surrounded by underscores (see Binding From Environment Variables) |
System properties |
Camel case, kebab case, or underscore notation |
Standard list syntax using |
We recommend that, when possible, properties are stored in lower-case kebab format, such as my.person.first-name=Rod.
|
Binding Maps
When binding to Map properties you may need to use a special bracket notation so that the original key value is preserved.
If the key is not surrounded by [], any characters that are not alpha-numeric, - or . are removed.
For example, consider binding the following properties to a Map<String,String>:
my.map.[/key1]=value1
my.map.[/key2]=value2
my.map./key3=value3my:
map:
"[/key1]": "value1"
"[/key2]": "value2"
"/key3": "value3"| For YAML files, the brackets need to be surrounded by quotes for the keys to be parsed properly. |
The properties above will bind to a Map with /key1, /key2 and key3 as the keys in the map.
The slash has been removed from key3 because it was not surrounded by square brackets.
When binding to scalar values, keys with . in them do not need to be surrounded by [].
Scalar values include enums and all types in the java.lang package except for Object.
Binding a.b=c to Map<String, String> will preserve the . in the key and return a Map with the entry {"a.b"="c"}.
For any other types you need to use the bracket notation if your key contains a ..
For example, binding a.b=c to Map<String, Object> will return a Map with the entry {"a"={"b"="c"}} whereas [a.b]=c will return a Map with the entry {"a.b"="c"}.
Binding From Environment Variables
Most operating systems impose strict rules around the names that can be used for environment variables.
For example, Linux shell variables can contain only letters (a to z or A to Z), numbers (0 to 9) or the underscore character (_).
By convention, Unix shell variables will also have their names in UPPERCASE.
Spring Boot’s relaxed binding rules are, as much as possible, designed to be compatible with these naming restrictions.
To convert a property name in the canonical-form to an environment variable name you can follow these rules:
-
Replace dots (
.) with underscores (_). -
Remove any dashes (
-). -
Convert to uppercase.
For example, the configuration property spring.main.log-startup-info would be an environment variable named SPRING_MAIN_LOGSTARTUPINFO.
Environment variables can also be used when binding to object lists.
To bind to a List, the element number should be surrounded with underscores in the variable name.
For example, the configuration property my.service[0].other would use an environment variable named MY_SERVICE_0_OTHER.
Support for binding from environment variables is applied to the systemEnvironment property source and to any additional property source whose name ends with -systemEnvironment.
Binding Maps From Environment Variables
When Spring Boot binds an environment variable to a property class, it lowercases the environment variable name before binding.
Most of the time this detail isn’t important, except when binding to Map properties.
The keys in the Map are always in lowercase, as seen in the following example:
@ConfigurationProperties(prefix = "my.props")
public class MyMapsProperties {
private final Map<String, String> values = new HashMap<>();
public Map<String, String> getValues() {
return this.values;
}
}
@ConfigurationProperties(prefix = "my.props")
class MyMapsProperties {
val values: Map<String, String> = HashMap()
}
When setting MY_PROPS_VALUES_KEY=value, the values Map contains a {"key"="value"} entry.
Only the environment variable name is lower-cased, not the value.
When setting MY_PROPS_VALUES_KEY=VALUE, the values Map contains a {"key"="VALUE"} entry.
2.8.7. Merging Complex Types
When lists are configured in more than one place, overriding works by replacing the entire list.
For example, assume a MyPojo object with name and description attributes that are null by default.
The following example exposes a list of MyPojo objects from MyProperties:
@ConfigurationProperties("my")
public class MyProperties {
private final List<MyPojo> list = new ArrayList<>();
public List<MyPojo> getList() {
return this.list;
}
}
@ConfigurationProperties("my")
class MyProperties {
val list: List<MyPojo> = ArrayList()
}
Consider the following configuration:
my.list[0].name=my name
my.list[0].description=my description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another namemy:
list:
- name: "my name"
description: "my description"
---
spring:
config:
activate:
on-profile: "dev"
my:
list:
- name: "my another name"If the dev profile is not active, MyProperties.list contains one MyPojo entry, as previously defined.
If the dev profile is enabled, however, the list still contains only one entry (with a name of my another name and a description of null).
This configuration does not add a second MyPojo instance to the list, and it does not merge the items.
When a List is specified in multiple profiles, the one with the highest priority (and only that one) is used.
Consider the following example:
my.list[0].name=my name
my.list[0].description=my description
my.list[1].name=another name
my.list[1].description=another description
#---
spring.config.activate.on-profile=dev
my.list[0].name=my another namemy:
list:
- name: "my name"
description: "my description"
- name: "another name"
description: "another description"
---
spring:
config:
activate:
on-profile: "dev"
my:
list:
- name: "my another name"In the preceding example, if the dev profile is active, MyProperties.list contains one MyPojo entry (with a name of my another name and a description of null).
For YAML, both comma-separated lists and YAML lists can be used for completely overriding the contents of the list.
For Map properties, you can bind with property values drawn from multiple sources.
However, for the same property in multiple sources, the one with the highest priority is used.
The following example exposes a Map<String, MyPojo> from MyProperties:
@ConfigurationProperties("my")
public class MyProperties {
private final Map<String, MyPojo> map = new LinkedHashMap<>();
public Map<String, MyPojo> getMap() {
return this.map;
}
}
@ConfigurationProperties("my")
class MyProperties {
val map: Map<String, MyPojo> = LinkedHashMap()
}
Consider the following configuration:
my.map.key1.name=my name 1
my.map.key1.description=my description 1
#---
spring.config.activate.on-profile=dev
my.map.key1.name=dev name 1
my.map.key2.name=dev name 2
my.map.key2.description=dev description 2my:
map:
key1:
name: "my name 1"
description: "my description 1"
---
spring:
config:
activate:
on-profile: "dev"
my:
map:
key1:
name: "dev name 1"
key2:
name: "dev name 2"
description: "dev description 2"If the dev profile is not active, MyProperties.map contains one entry with key key1 (with a name of my name 1 and a description of my description 1).
If the dev profile is enabled, however, map contains two entries with keys key1 (with a name of dev name 1 and a description of my description 1) and key2 (with a name of dev name 2 and a description of dev description 2).
| The preceding merging rules apply to properties from all property sources, and not just files. |
2.8.8. Properties Conversion
Spring Boot attempts to coerce the external application properties to the right type when it binds to the @ConfigurationProperties beans.
If you need custom type conversion, you can provide a ConversionService bean (with a bean named conversionService) or custom property editors (through a CustomEditorConfigurer bean) or custom Converters (with bean definitions annotated as @ConfigurationPropertiesBinding).
As this bean is requested very early during the application lifecycle, make sure to limit the dependencies that your ConversionService is using.
Typically, any dependency that you require may not be fully initialized at creation time.
You may want to rename your custom ConversionService if it is not required for configuration keys coercion and only rely on custom converters qualified with @ConfigurationPropertiesBinding.
|
Converting Durations
Spring Boot has dedicated support for expressing durations.
If you expose a java.time.Duration property, the following formats in application properties are available:
-
A regular
longrepresentation (using milliseconds as the default unit unless a@DurationUnithas been specified) -
The standard ISO-8601 format used by
java.time.Duration -
A more readable format where the value and the unit are coupled (
10smeans 10 seconds)
Consider the following example:
@ConfigurationProperties("my")
public class MyProperties {
@DurationUnit(ChronoUnit.SECONDS)
private Duration sessionTimeout = Duration.ofSeconds(30);
private Duration readTimeout = Duration.ofMillis(1000);
}
@ConfigurationProperties("my")
class MyProperties {
@DurationUnit(ChronoUnit.SECONDS)
var sessionTimeout = Duration.ofSeconds(30)
var readTimeout = Duration.ofMillis(1000)
}
To specify a session timeout of 30 seconds, 30, PT30S and 30s are all equivalent.
A read timeout of 500ms can be specified in any of the following form: 500, PT0.5S and 500ms.
You can also use any of the supported units. These are:
-
nsfor nanoseconds -
usfor microseconds -
msfor milliseconds -
sfor seconds -
mfor minutes -
hfor hours -
dfor days
The default unit is milliseconds and can be overridden using @DurationUnit as illustrated in the sample above.
If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:
@ConfigurationProperties("my")
public class MyProperties {
public MyProperties(@DurationUnit(ChronoUnit.SECONDS) @DefaultValue("30s") Duration sessionTimeout,
@DefaultValue("1000ms") Duration readTimeout) {
this.sessionTimeout = sessionTimeout;
this.readTimeout = readTimeout;
}
}
@ConfigurationProperties("my")
class MyProperties(@param:DurationUnit(ChronoUnit.SECONDS) @param:DefaultValue("30s") val sessionTimeout: Duration,
@param:DefaultValue("1000ms") val readTimeout: Duration)
If you are upgrading a Long property, make sure to define the unit (using @DurationUnit) if it is not milliseconds.
Doing so gives a transparent upgrade path while supporting a much richer format.
|
Converting Periods
In addition to durations, Spring Boot can also work with java.time.Period type.
The following formats can be used in application properties:
-
An regular
intrepresentation (using days as the default unit unless a@PeriodUnithas been specified) -
The standard ISO-8601 format used by
java.time.Period -
A simpler format where the value and the unit pairs are coupled (
1y3dmeans 1 year and 3 days)
The following units are supported with the simple format:
-
yfor years -
mfor months -
wfor weeks -
dfor days
The java.time.Period type never actually stores the number of weeks, it is a shortcut that means “7 days”.
|
Converting Data Sizes
Spring Framework has a DataSize value type that expresses a size in bytes.
If you expose a DataSize property, the following formats in application properties are available:
-
A regular
longrepresentation (using bytes as the default unit unless a@DataSizeUnithas been specified) -
A more readable format where the value and the unit are coupled (
10MBmeans 10 megabytes)
Consider the following example:
@ConfigurationProperties("my")
public class MyProperties {
@DataSizeUnit(DataUnit.MEGABYTES)
private DataSize bufferSize = DataSize.ofMegabytes(2);
private DataSize sizeThreshold = DataSize.ofBytes(512);
}
@ConfigurationProperties("my")
class MyProperties {
@DataSizeUnit(DataUnit.MEGABYTES)
var bufferSize = DataSize.ofMegabytes(2)
var sizeThreshold = DataSize.ofBytes(512)
}
To specify a buffer size of 10 megabytes, 10 and 10MB are equivalent.
A size threshold of 256 bytes can be specified as 256 or 256B.
You can also use any of the supported units. These are:
-
Bfor bytes -
KBfor kilobytes -
MBfor megabytes -
GBfor gigabytes -
TBfor terabytes
The default unit is bytes and can be overridden using @DataSizeUnit as illustrated in the sample above.
If you prefer to use constructor binding, the same properties can be exposed, as shown in the following example:
@ConfigurationProperties("my")
public class MyProperties {
public MyProperties(@DataSizeUnit(DataUnit.MEGABYTES) @DefaultValue("2MB") DataSize bufferSize,
@DefaultValue("512B") DataSize sizeThreshold) {
this.bufferSize = bufferSize;
this.sizeThreshold = sizeThreshold;
}
}
@ConfigurationProperties("my")
class MyProperties(@param:DataSizeUnit(DataUnit.MEGABYTES) @param:DefaultValue("2MB") val bufferSize: DataSize,
@param:DefaultValue("512B") val sizeThreshold: DataSize)
If you are upgrading a Long property, make sure to define the unit (using @DataSizeUnit) if it is not bytes.
Doing so gives a transparent upgrade path while supporting a much richer format.
|
2.8.9. @ConfigurationProperties Validation
Spring Boot attempts to validate @ConfigurationProperties classes whenever they are annotated with Spring’s @Validated annotation.
You can use JSR-303 jakarta.validation constraint annotations directly on your configuration class.
To do so, ensure that a compliant JSR-303 implementation is on your classpath and then add constraint annotations to your fields, as shown in the following example:
@ConfigurationProperties("my.service")
@Validated
public class MyProperties {
@NotNull
private InetAddress remoteAddress;
}
@ConfigurationProperties("my.service")
@Validated
class MyProperties {
var remoteAddress: @NotNull InetAddress? = null
}
You can also trigger validation by annotating the @Bean method that creates the configuration properties with @Validated.
|
To ensure that validation is always triggered for nested properties, even when no properties are found, the associated field must be annotated with @Valid.
The following example builds on the preceding MyProperties example:
@ConfigurationProperties("my.service")
@Validated
public class MyProperties {
@NotNull
private InetAddress remoteAddress;
@Valid
private final Security security = new Security();
public static class Security {
@NotEmpty
private String username;
}
}
@ConfigurationProperties("my.service")
@Validated
class MyProperties {
var remoteAddress: @NotNull InetAddress? = null
@Valid
val security = Security()
class Security {
@NotEmpty
var username: String? = null
}
}
You can also add a custom Spring Validator by creating a bean definition called configurationPropertiesValidator.
The @Bean method should be declared static.
The configuration properties validator is created very early in the application’s lifecycle, and declaring the @Bean method as static lets the bean be created without having to instantiate the @Configuration class.
Doing so avoids any problems that may be caused by early instantiation.
The spring-boot-actuator module includes an endpoint that exposes all @ConfigurationProperties beans.
Point your web browser to /actuator/configprops or use the equivalent JMX endpoint.
See the "Production ready features" section for details.
|
2.8.10. @ConfigurationProperties vs. @Value
The @Value annotation is a core container feature, and it does not provide the same features as type-safe configuration properties.
The following table summarizes the features that are supported by @ConfigurationProperties and @Value:
| Feature | @ConfigurationProperties |
@Value |
|---|---|---|
Yes |
Limited (see note below) |
|
Yes |
No |
|
|
No |
Yes |
|
If you do want to use For example, |
If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with @ConfigurationProperties.
Doing so will provide you with structured, type-safe object that you can inject into your own beans.
SpEL expressions from application property files are not processed at time of parsing these files and populating the environment.
However, it is possible to write a SpEL expression in @Value.
If the value of a property from an application property file is a SpEL expression, it will be evaluated when consumed through @Value.
3. Profiles
Spring Profiles provide a way to segregate parts of your application configuration and make it be available only in certain environments.
Any @Component, @Configuration or @ConfigurationProperties can be marked with @Profile to limit when it is loaded, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@Profile("production")
public class ProductionConfiguration {
// ...
}
@Configuration(proxyBeanMethods = false)
@Profile("production")
class ProductionConfiguration {
// ...
}
If @ConfigurationProperties beans are registered through @EnableConfigurationProperties instead of automatic scanning, the @Profile annotation needs to be specified on the @Configuration class that has the @EnableConfigurationProperties annotation.
In the case where @ConfigurationProperties are scanned, @Profile can be specified on the @ConfigurationProperties class itself.
|
You can use a spring.profiles.active Environment property to specify which profiles are active.
You can specify the property in any of the ways described earlier in this chapter.
For example, you could include it in your application.properties, as shown in the following example:
spring.profiles.active=dev,hsqldbspring:
profiles:
active: "dev,hsqldb"You could also specify it on the command line by using the following switch: --spring.profiles.active=dev,hsqldb.
If no profile is active, a default profile is enabled.
The name of the default profile is default and it can be tuned using the spring.profiles.default Environment property, as shown in the following example:
spring.profiles.default=nonespring:
profiles:
default: "none"spring.profiles.active and spring.profiles.default can only be used in non-profile-specific documents.
This means they cannot be included in profile specific files or documents activated by spring.config.activate.on-profile.
For example, the second document configuration is invalid:
# this document is valid
spring.profiles.active=prod
#---
# this document is invalid
spring.config.activate.on-profile=prod
spring.profiles.active=metrics# this document is valid
spring:
profiles:
active: "prod"
---
# this document is invalid
spring:
config:
activate:
on-profile: "prod"
profiles:
active: "metrics"3.1. Adding Active Profiles
The spring.profiles.active property follows the same ordering rules as other properties: The highest PropertySource wins.
This means that you can specify active profiles in application.properties and then replace them by using the command line switch.
Sometimes, it is useful to have properties that add to the active profiles rather than replace them.
The spring.profiles.include property can be used to add active profiles on top of those activated by the spring.profiles.active property.
The SpringApplication entry point also has a Java API for setting additional profiles.
See the setAdditionalProfiles() method in SpringApplication.
For example, when an application with the following properties is run, the common and local profiles will be activated even when it runs using the --spring.profiles.active switch:
spring.profiles.include[0]=common
spring.profiles.include[1]=localspring:
profiles:
include:
- "common"
- "local"
Similar to spring.profiles.active, spring.profiles.include can only be used in non-profile-specific documents.
This means it cannot be included in profile specific files or documents activated by spring.config.activate.on-profile.
|
Profile groups, which are described in the next section can also be used to add active profiles if a given profile is active.
3.2. Profile Groups
Occasionally the profiles that you define and use in your application are too fine-grained and become cumbersome to use.
For example, you might have proddb and prodmq profiles that you use to enable database and messaging features independently.
To help with this, Spring Boot lets you define profile groups. A profile group allows you to define a logical name for a related group of profiles.
For example, we can create a production group that consists of our proddb and prodmq profiles.
spring.profiles.group.production[0]=proddb
spring.profiles.group.production[1]=prodmqspring:
profiles:
group:
production:
- "proddb"
- "prodmq"Our application can now be started using --spring.profiles.active=production to activate the production, proddb and prodmq profiles in one hit.
Similar to spring.profiles.active and spring.profiles.include, spring.profiles.group can only be used in non-profile-specific documents.
This means it cannot be included in profile specific files or documents activated by spring.config.activate.on-profile.
|
3.3. Programmatically Setting Profiles
You can programmatically set active profiles by calling SpringApplication.setAdditionalProfiles(…) before your application runs.
It is also possible to activate profiles by using Spring’s ConfigurableEnvironment interface.
3.4. Profile-specific Configuration Files
Profile-specific variants of both application.properties (or application.yaml) and files referenced through @ConfigurationProperties are considered as files and loaded.
See "Profile Specific Files" for details.
4. Logging
Spring Boot uses Commons Logging for all internal logging but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging, Log4j2, and Logback. In each case, loggers are pre-configured to use console output with optional file output also available.
By default, if you use the “Starters”, Logback is used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J, or SLF4J all work correctly.
| There are a lot of logging frameworks available for Java. Do not worry if the above list seems confusing. Generally, you do not need to change your logging dependencies and the Spring Boot defaults work just fine. |
| When you deploy your application to a servlet container or application server, logging performed with the Java Util Logging API is not routed into your application’s logs. This prevents logging performed by the container or other applications that have been deployed to it from appearing in your application’s logs. |
4.1. Log Format
The default log output from Spring Boot resembles the following example:
2024-11-21T07:54:17.816Z INFO 109369 --- [myapp] [ main] o.s.b.d.f.logexample.MyApplication : Starting MyApplication using Java 17.0.13 with PID 109369 (/opt/apps/myapp.jar started by myuser in /opt/apps/) 2024-11-21T07:54:17.836Z INFO 109369 --- [myapp] [ main] o.s.b.d.f.logexample.MyApplication : No active profile set, falling back to 1 default profile: "default" 2024-11-21T07:54:22.108Z INFO 109369 --- [myapp] [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port 8080 (http) 2024-11-21T07:54:22.155Z INFO 109369 --- [myapp] [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2024-11-21T07:54:22.155Z INFO 109369 --- [myapp] [ main] o.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/10.1.33] 2024-11-21T07:54:22.402Z INFO 109369 --- [myapp] [ main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2024-11-21T07:54:22.424Z INFO 109369 --- [myapp] [ main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 4342 ms 2024-11-21T07:54:24.813Z INFO 109369 --- [myapp] [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port 8080 (http) with context path '' 2024-11-21T07:54:24.865Z INFO 109369 --- [myapp] [ main] o.s.b.d.f.logexample.MyApplication : Started MyApplication in 8.97 seconds (process running for 10.255)
The following items are output:
-
Date and Time: Millisecond precision and easily sortable.
-
Log Level:
ERROR,WARN,INFO,DEBUG, orTRACE. -
Process ID.
-
A
---separator to distinguish the start of actual log messages. -
Application name: Enclosed in square brackets (logged by default only if
spring.application.nameis set) -
Thread name: Enclosed in square brackets (may be truncated for console output).
-
Correlation ID: If tracing is enabled (not shown in the sample above)
-
Logger name: This is usually the source class name (often abbreviated).
-
The log message.
Logback does not have a FATAL level.
It is mapped to ERROR.
|
If you have a spring.application.name property but don’t want it logged you can set logging.include-application-name to false.
|
4.2. Console Output
The default log configuration echoes messages to the console as they are written.
By default, ERROR-level, WARN-level, and INFO-level messages are logged.
You can also enable a “debug” mode by starting your application with a --debug flag.
$ java -jar myapp.jar --debug
You can also specify debug=true in your application.properties.
|
When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate, and Spring Boot) are configured to output more information.
Enabling the debug mode does not configure your application to log all messages with DEBUG level.
Alternatively, you can enable a “trace” mode by starting your application with a --trace flag (or trace=true in your application.properties).
Doing so enables trace logging for a selection of core loggers (embedded container, Hibernate schema generation, and the whole Spring portfolio).
4.2.1. Color-coded Output
If your terminal supports ANSI, color output is used to aid readability.
You can set spring.output.ansi.enabled to a supported value to override the auto-detection.
Color coding is configured by using the %clr conversion word.
In its simplest form, the converter colors the output according to the log level, as shown in the following example:
%clr(%5p)The following table describes the mapping of log levels to colors:
| Level | Color |
|---|---|
|
Red |
|
Red |
|
Yellow |
|
Green |
|
Green |
|
Green |
Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow, use the following setting:
%clr(%d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX}){yellow}The following colors and styles are supported:
-
blue -
cyan -
faint -
green -
magenta -
red -
yellow
4.3. File Output
By default, Spring Boot logs only to the console and does not write log files.
If you want to write log files in addition to the console output, you need to set a logging.file.name or logging.file.path property (for example, in your application.properties).
If both properties are set, logging.file.path is ignored and only logging.file.name is used.
The following table shows how the logging.* properties can be used together:
logging.file.name |
logging.file.path |
Description |
|---|---|---|
(none) |
(none) |
Console only logging. |
Specific file (for example, |
(none) |
Writes to the location specified by |
(none) |
Specific directory (for example, |
Writes |
Specific file |
Specific directory |
Writes to the location specified by |
Log files rotate when they reach 10 MB and, as with console output, ERROR-level, WARN-level, and INFO-level messages are logged by default.
Logging properties are independent of the actual logging infrastructure.
As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.
|
4.4. File Rotation
If you are using the Logback, it is possible to fine-tune log rotation settings using your application.properties or application.yaml file.
For all other logging system, you will need to configure rotation settings directly yourself (for example, if you use Log4j2 then you could add a log4j2.xml or log4j2-spring.xml file).
The following rotation policy properties are supported:
| Name | Description |
|---|---|
|
The filename pattern used to create log archives. |
|
If log archive cleanup should occur when the application starts. |
|
The maximum size of log file before it is archived. |
|
The maximum amount of size log archives can take before being deleted. |
|
The maximum number of archive log files to keep (defaults to 7). |
4.5. Log Levels
All the supported logging systems can have the logger levels set in the Spring Environment (for example, in application.properties) by using logging.level.<logger-name>=<level> where level is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, or OFF.
The root logger can be configured by using logging.level.root.
The following example shows potential logging settings in application.properties:
logging.level.root=warn
logging.level.org.springframework.web=debug
logging.level.org.hibernate=errorlogging:
level:
root: "warn"
org.springframework.web: "debug"
org.hibernate: "error"It is also possible to set logging levels using environment variables.
For example, LOGGING_LEVEL_ORG_SPRINGFRAMEWORK_WEB=DEBUG will set org.springframework.web to DEBUG.
The above approach will only work for package level logging.
Since relaxed binding always converts environment variables to lowercase, it is not possible to configure logging for an individual class in this way.
If you need to configure logging for a class, you can use the SPRING_APPLICATION_JSON variable.
|
4.6. Log Groups
It is often useful to be able to group related loggers together so that they can all be configured at the same time. For example, you might commonly change the logging levels for all Tomcat related loggers, but you can not easily remember top level packages.
To help with this, Spring Boot allows you to define logging groups in your Spring Environment.
For example, here is how you could define a “tomcat” group by adding it to your application.properties:
logging.group.tomcat=org.apache.catalina,org.apache.coyote,org.apache.tomcatlogging:
group:
tomcat: "org.apache.catalina,org.apache.coyote,org.apache.tomcat"Once defined, you can change the level for all the loggers in the group with a single line:
logging.level.tomcat=tracelogging:
level:
tomcat: "trace"Spring Boot includes the following pre-defined logging groups that can be used out-of-the-box:
| Name | Loggers |
|---|---|
web |
|
sql |
|
4.7. Using a Log Shutdown Hook
In order to release logging resources when your application terminates, a shutdown hook that will trigger log system cleanup when the JVM exits is provided.
This shutdown hook is registered automatically unless your application is deployed as a war file.
If your application has complex context hierarchies the shutdown hook may not meet your needs.
If it does not, disable the shutdown hook and investigate the options provided directly by the underlying logging system.
For example, Logback offers context selectors which allow each Logger to be created in its own context.
You can use the logging.register-shutdown-hook property to disable the shutdown hook.
Setting it to false will disable the registration.
You can set the property in your application.properties or application.yaml file:
logging.register-shutdown-hook=falselogging:
register-shutdown-hook: false4.8. Custom Log Configuration
The various logging systems can be activated by including the appropriate libraries on the classpath and can be further customized by providing a suitable configuration file in the root of the classpath or in a location specified by the following Spring Environment property: logging.config.
You can force Spring Boot to use a particular logging system by using the org.springframework.boot.logging.LoggingSystem system property.
The value should be the fully qualified class name of a LoggingSystem implementation.
You can also disable Spring Boot’s logging configuration entirely by using a value of none.
Since logging is initialized before the ApplicationContext is created, it is not possible to control logging from @PropertySources in Spring @Configuration files.
The only way to change the logging system or disable it entirely is through System properties.
|
Depending on your logging system, the following files are loaded:
| Logging System | Customization |
|---|---|
Logback |
|
Log4j2 |
|
JDK (Java Util Logging) |
|
When possible, we recommend that you use the -spring variants for your logging configuration (for example, logback-spring.xml rather than logback.xml).
If you use standard configuration locations, Spring cannot completely control log initialization.
|
| There are known classloading issues with Java Util Logging that cause problems when running from an 'executable jar'. We recommend that you avoid it when running from an 'executable jar' if at all possible. |
To help with the customization, some other properties are transferred from the Spring Environment to System properties.
This allows the properties to be consumed by logging system configuration. For example, setting logging.file.name in application.properties or LOGGING_FILE_NAME as an environment variable will result in the LOG_FILE System property being set.
The properties that are transferred are described in the following table:
| Spring Environment | System Property | Comments |
|---|---|---|
|
|
The conversion word used when logging exceptions. |
|
|
If defined, it is used in the default log configuration. |
|
|
If defined, it is used in the default log configuration. |
|
|
The log pattern to use on the console (stdout). |
|
|
Appender pattern for log date format. |
|
|
The charset to use for console logging. |
|
|
The log level threshold to use for console logging. |
|
|
The log pattern to use in a file (if |
|
|
The charset to use for file logging (if |
|
|
The log level threshold to use for file logging. |
|
|
The format to use when rendering the log level (default |
|
|
The current process ID (discovered if possible and when not already defined as an OS environment variable). |
If you use Logback, the following properties are also transferred:
| Spring Environment | System Property | Comments |
|---|---|---|
|
|
Pattern for rolled-over log file names (default |
|
|
Whether to clean the archive log files on startup. |
|
|
Maximum log file size. |
|
|
Total size of log backups to be kept. |
|
|
Maximum number of archive log files to keep. |
All the supported logging systems can consult System properties when parsing their configuration files.
See the default configurations in spring-boot.jar for examples:
|
If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework.
Notably, if you use Logback, you should use |
|
You can add MDC and other ad-hoc content to log lines by overriding only the 2019-08-30 12:30:04.031 user:someone INFO 22174 --- [ nio-8080-exec-0] demo.Controller Handling authenticated request |
4.9. Logback Extensions
Spring Boot includes a number of extensions to Logback that can help with advanced configuration.
You can use these extensions in your logback-spring.xml configuration file.
Because the standard logback.xml configuration file is loaded too early, you cannot use extensions in it.
You need to either use logback-spring.xml or define a logging.config property.
|
| The extensions cannot be used with Logback’s configuration scanning. If you attempt to do so, making changes to the configuration file results in an error similar to one of the following being logged: |
ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProperty], current ElementPath is [[configuration][springProperty]] ERROR in ch.qos.logback.core.joran.spi.Interpreter@4:71 - no applicable action for [springProfile], current ElementPath is [[configuration][springProfile]]
4.9.1. Profile-specific Configuration
The <springProfile> tag lets you optionally include or exclude sections of configuration based on the active Spring profiles.
Profile sections are supported anywhere within the <configuration> element.
Use the name attribute to specify which profile accepts the configuration.
The <springProfile> tag can contain a profile name (for example staging) or a profile expression.
A profile expression allows for more complicated profile logic to be expressed, for example production & (eu-central | eu-west).
Check the Spring Framework reference guide for more details.
The following listing shows three sample profiles:
<springProfile name="staging">
<!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>
<springProfile name="dev | staging">
<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>
<springProfile name="!production">
<!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>4.9.2. Environment Properties
The <springProperty> tag lets you expose properties from the Spring Environment for use within Logback.
Doing so can be useful if you want to access values from your application.properties file in your Logback configuration.
The tag works in a similar way to Logback’s standard <property> tag.
However, rather than specifying a direct value, you specify the source of the property (from the Environment).
If you need to store the property somewhere other than in local scope, you can use the scope attribute.
If you need a fallback value (in case the property is not set in the Environment), you can use the defaultValue attribute.
The following example shows how to expose properties for use within Logback:
<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
defaultValue="localhost"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
<remoteHost>${fluentHost}</remoteHost>
...
</appender>
The source must be specified in kebab case (such as my.property-name).
However, properties can be added to the Environment by using the relaxed rules.
|
4.10. Log4j2 Extensions
Spring Boot includes a number of extensions to Log4j2 that can help with advanced configuration.
You can use these extensions in any log4j2-spring.xml configuration file.
Because the standard log4j2.xml configuration file is loaded too early, you cannot use extensions in it.
You need to either use log4j2-spring.xml or define a logging.config property.
|
The extensions supersede the Spring Boot support provided by Log4J.
You should make sure not to include the org.apache.logging.log4j:log4j-spring-boot module in your build.
|
4.10.1. Profile-specific Configuration
The <SpringProfile> tag lets you optionally include or exclude sections of configuration based on the active Spring profiles.
Profile sections are supported anywhere within the <Configuration> element.
Use the name attribute to specify which profile accepts the configuration.
The <SpringProfile> tag can contain a profile name (for example staging) or a profile expression.
A profile expression allows for more complicated profile logic to be expressed, for example production & (eu-central | eu-west).
Check the Spring Framework reference guide for more details.
The following listing shows three sample profiles:
<SpringProfile name="staging">
<!-- configuration to be enabled when the "staging" profile is active -->
</SpringProfile>
<SpringProfile name="dev | staging">
<!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</SpringProfile>
<SpringProfile name="!production">
<!-- configuration to be enabled when the "production" profile is not active -->
</SpringProfile>4.10.2. Environment Properties Lookup
If you want to refer to properties from your Spring Environment within your Log4j2 configuration you can use spring: prefixed lookups.
Doing so can be useful if you want to access values from your application.properties file in your Log4j2 configuration.
The following example shows how to set a Log4j2 property named applicationName that reads spring.application.name from the Spring Environment:
<Properties>
<Property name="applicationName">${spring:spring.application.name}</Property>
</Properties>
The lookup key should be specified in kebab case (such as my.property-name).
|
4.10.3. Log4j2 System Properties
Log4j2 supports a number of System Properties that can be used to configure various items.
For example, the log4j2.skipJansi system property can be used to configure if the ConsoleAppender will try to use a Jansi output stream on Windows.
All system properties that are loaded after the Log4j2 initialization can be obtained from the Spring Environment.
For example, you could add log4j2.skipJansi=false to your application.properties file to have the ConsoleAppender use Jansi on Windows.
The Spring Environment is only considered when system properties and OS environment variables do not contain the value being loaded.
|
System properties that are loaded during early Log4j2 initialization cannot reference the Spring Environment.
For example, the property Log4j2 uses to allow the default Log4j2 implementation to be chosen is used before the Spring Environment is available.
|
5. Internationalization
Spring Boot supports localized messages so that your application can cater to users of different language preferences.
By default, Spring Boot looks for the presence of a messages resource bundle at the root of the classpath.
The auto-configuration applies when the default properties file for the configured resource bundle is available (messages.properties by default).
If your resource bundle contains only language-specific properties files, you are required to add the default.
If no properties file is found that matches any of the configured base names, there will be no auto-configured MessageSource.
|
The basename of the resource bundle as well as several other attributes can be configured using the spring.messages namespace, as shown in the following example:
spring.messages.basename=messages,config.i18n.messages
spring.messages.fallback-to-system-locale=falsespring:
messages:
basename: "messages,config.i18n.messages"
fallback-to-system-locale: false
spring.messages.basename supports comma-separated list of locations, either a package qualifier or a resource resolved from the classpath root.
|
See MessageSourceProperties for more supported options.
6. Aspect-Oriented Programming
Spring Boot provides auto-configuration for aspect-oriented programming (AOP). You can learn more about AOP with Spring in the Spring Framework reference documentation.
By default, Spring Boot’s auto-configuration configures Spring AOP to use CGLib proxies.
To use JDK proxies instead, set spring.aop.proxy-target-class to false.
If AspectJ is on the classpath, Spring Boot’s auto-configuration will automatically enable AspectJ auto proxy such that @EnableAspectJAutoProxy is not required.
7. JSON
Spring Boot provides integration with three JSON mapping libraries:
-
Gson
-
Jackson
-
JSON-B
Jackson is the preferred and default library.
7.1. Jackson
Auto-configuration for Jackson is provided and Jackson is part of spring-boot-starter-json.
When Jackson is on the classpath an ObjectMapper bean is automatically configured.
Several configuration properties are provided for customizing the configuration of the ObjectMapper.
7.1.1. Custom Serializers and Deserializers
If you use Jackson to serialize and deserialize JSON data, you might want to write your own JsonSerializer and JsonDeserializer classes.
Custom serializers are usually registered with Jackson through a module, but Spring Boot provides an alternative @JsonComponent annotation that makes it easier to directly register Spring Beans.
You can use the @JsonComponent annotation directly on JsonSerializer, JsonDeserializer or KeyDeserializer implementations.
You can also use it on classes that contain serializers/deserializers as inner classes, as shown in the following example:
@JsonComponent
public class MyJsonComponent {
public static class Serializer extends JsonSerializer<MyObject> {
@Override
public void serialize(MyObject value, JsonGenerator jgen, SerializerProvider serializers) throws IOException {
jgen.writeStartObject();
jgen.writeStringField("name", value.getName());
jgen.writeNumberField("age", value.getAge());
jgen.writeEndObject();
}
}
public static class Deserializer extends JsonDeserializer<MyObject> {
@Override
public MyObject deserialize(JsonParser jsonParser, DeserializationContext ctxt) throws IOException {
ObjectCodec codec = jsonParser.getCodec();
JsonNode tree = codec.readTree(jsonParser);
String name = tree.get("name").textValue();
int age = tree.get("age").intValue();
return new MyObject(name, age);
}
}
}
@JsonComponent
class MyJsonComponent {
class Serializer : JsonSerializer<MyObject>() {
@Throws(IOException::class)
override fun serialize(value: MyObject, jgen: JsonGenerator, serializers: SerializerProvider) {
jgen.writeStartObject()
jgen.writeStringField("name", value.name)
jgen.writeNumberField("age", value.age)
jgen.writeEndObject()
}
}
class Deserializer : JsonDeserializer<MyObject>() {
@Throws(IOException::class, JsonProcessingException::class)
override fun deserialize(jsonParser: JsonParser, ctxt: DeserializationContext): MyObject {
val codec = jsonParser.codec
val tree = codec.readTree<JsonNode>(jsonParser)
val name = tree["name"].textValue()
val age = tree["age"].intValue()
return MyObject(name, age)
}
}
}
All @JsonComponent beans in the ApplicationContext are automatically registered with Jackson.
Because @JsonComponent is meta-annotated with @Component, the usual component-scanning rules apply.
Spring Boot also provides JsonObjectSerializer and JsonObjectDeserializer base classes that provide useful alternatives to the standard Jackson versions when serializing objects.
See JsonObjectSerializer and JsonObjectDeserializer in the Javadoc for details.
The example above can be rewritten to use JsonObjectSerializer/JsonObjectDeserializer as follows:
@JsonComponent
public class MyJsonComponent {
public static class Serializer extends JsonObjectSerializer<MyObject> {
@Override
protected void serializeObject(MyObject value, JsonGenerator jgen, SerializerProvider provider)
throws IOException {
jgen.writeStringField("name", value.getName());
jgen.writeNumberField("age", value.getAge());
}
}
public static class Deserializer extends JsonObjectDeserializer<MyObject> {
@Override
protected MyObject deserializeObject(JsonParser jsonParser, DeserializationContext context, ObjectCodec codec,
JsonNode tree) throws IOException {
String name = nullSafeValue(tree.get("name"), String.class);
int age = nullSafeValue(tree.get("age"), Integer.class);
return new MyObject(name, age);
}
}
}
`object`
@JsonComponent
class MyJsonComponent {
class Serializer : JsonObjectSerializer<MyObject>() {
@Throws(IOException::class)
override fun serializeObject(value: MyObject, jgen: JsonGenerator, provider: SerializerProvider) {
jgen.writeStringField("name", value.name)
jgen.writeNumberField("age", value.age)
}
}
class Deserializer : JsonObjectDeserializer<MyObject>() {
@Throws(IOException::class)
override fun deserializeObject(jsonParser: JsonParser, context: DeserializationContext,
codec: ObjectCodec, tree: JsonNode): MyObject {
val name = nullSafeValue(tree["name"], String::class.java)
val age = nullSafeValue(tree["age"], Int::class.java)
return MyObject(name, age)
}
}
}
7.1.2. Mixins
Jackson has support for mixins that can be used to mix additional annotations into those already declared on a target class.
Spring Boot’s Jackson auto-configuration will scan your application’s packages for classes annotated with @JsonMixin and register them with the auto-configured ObjectMapper.
The registration is performed by Spring Boot’s JsonMixinModule.
8. Task Execution and Scheduling
In the absence of an Executor bean in the context, Spring Boot auto-configures an AsyncTaskExecutor.
When virtual threads are enabled (using Java 21+ and spring.threads.virtual.enabled set to true) this will be a SimpleAsyncTaskExecutor that uses virtual threads.
Otherwise, it will be a ThreadPoolTaskExecutor with sensible defaults.
In either case, the auto-configured executor will be automatically used for:
-
asynchronous task execution (
@EnableAsync) -
Spring for GraphQL’s asynchronous handling of
Callablereturn values from controller methods -
Spring MVC’s asynchronous request processing
-
Spring WebFlux’s blocking execution support
|
If you have defined a custom The auto-configured |
When a ThreadPoolTaskExecutor is auto-configured, the thread pool uses 8 core threads that can grow and shrink according to the load.
Those default settings can be fine-tuned using the spring.task.execution namespace, as shown in the following example:
spring.task.execution.pool.max-size=16
spring.task.execution.pool.queue-capacity=100
spring.task.execution.pool.keep-alive=10sspring:
task:
execution:
pool:
max-size: 16
queue-capacity: 100
keep-alive: "10s"This changes the thread pool to use a bounded queue so that when the queue is full (100 tasks), the thread pool increases to maximum 16 threads. Shrinking of the pool is more aggressive as threads are reclaimed when they are idle for 10 seconds (rather than 60 seconds by default).
A scheduler can also be auto-configured if it needs to be associated with scheduled task execution (using @EnableScheduling for instance).
If virtual threads are enabled (using Java 21+ and spring.threads.virtual.enabled set to true) this will be a SimpleAsyncTaskScheduler that uses virtual threads.
This SimpleAsyncTaskScheduler will ignore any pooling related properties.
If virtual threads are not enabled, it will be a ThreadPoolTaskScheduler with sensible defaults.
The ThreadPoolTaskScheduler uses one thread by default and its settings can be fine-tuned using the spring.task.scheduling namespace, as shown in the following example:
spring.task.scheduling.thread-name-prefix=scheduling-
spring.task.scheduling.pool.size=2spring:
task:
scheduling:
thread-name-prefix: "scheduling-"
pool:
size: 2A ThreadPoolTaskExecutorBuilder bean, a SimpleAsyncTaskExecutorBuilder bean, a ThreadPoolTaskSchedulerBuilder bean and a SimpleAsyncTaskSchedulerBuilder are made available in the context if a custom executor or scheduler needs to be created.
The SimpleAsyncTaskExecutorBuilder and SimpleAsyncTaskSchedulerBuilder beans are auto-configured to use virtual threads if they are enabled (using Java 21+ and spring.threads.virtual.enabled set to true).
9. Testing
Spring Boot provides a number of utilities and annotations to help when testing your application.
Test support is provided by two modules: spring-boot-test contains core items, and spring-boot-test-autoconfigure supports auto-configuration for tests.
Most developers use the spring-boot-starter-test “Starter”, which imports both Spring Boot test modules as well as JUnit Jupiter, AssertJ, Hamcrest, and a number of other useful libraries.
|
If you have tests that use JUnit 4, JUnit 5’s vintage engine can be used to run them.
To use the vintage engine, add a dependency on |
hamcrest-core is excluded in favor of org.hamcrest:hamcrest that is part of spring-boot-starter-test.
9.1. Test Scope Dependencies
The spring-boot-starter-test “Starter” (in the test scope) contains the following provided libraries:
-
JUnit 5: The de-facto standard for unit testing Java applications.
-
Spring Test & Spring Boot Test: Utilities and integration test support for Spring Boot applications.
-
AssertJ: A fluent assertion library.
-
Hamcrest: A library of matcher objects (also known as constraints or predicates).
-
Mockito: A Java mocking framework.
-
JSONassert: An assertion library for JSON.
-
JsonPath: XPath for JSON.
-
Awaitility: A library for testing asynchronous systems.
We generally find these common libraries to be useful when writing tests. If these libraries do not suit your needs, you can add additional test dependencies of your own.
9.2. Testing Spring Applications
One of the major advantages of dependency injection is that it should make your code easier to unit test.
You can instantiate objects by using the new operator without even involving Spring.
You can also use mock objects instead of real dependencies.
Often, you need to move beyond unit testing and start integration testing (with a Spring ApplicationContext).
It is useful to be able to perform integration testing without requiring deployment of your application or needing to connect to other infrastructure.
The Spring Framework includes a dedicated test module for such integration testing.
You can declare a dependency directly to org.springframework:spring-test or use the spring-boot-starter-test “Starter” to pull it in transitively.
If you have not used the spring-test module before, you should start by reading the relevant section of the Spring Framework reference documentation.
9.3. Testing Spring Boot Applications
A Spring Boot application is a Spring ApplicationContext, so nothing very special has to be done to test it beyond what you would normally do with a vanilla Spring context.
External properties, logging, and other features of Spring Boot are installed in the context by default only if you use SpringApplication to create it.
|
Spring Boot provides a @SpringBootTest annotation, which can be used as an alternative to the standard spring-test @ContextConfiguration annotation when you need Spring Boot features.
The annotation works by creating the ApplicationContext used in your tests through SpringApplication.
In addition to @SpringBootTest a number of other annotations are also provided for testing more specific slices of an application.
If you are using JUnit 4, do not forget to also add @RunWith(SpringRunner.class) to your test, otherwise the annotations will be ignored.
If you are using JUnit 5, there is no need to add the equivalent @ExtendWith(SpringExtension.class) as @SpringBootTest and the other @…Test annotations are already annotated with it.
|
By default, @SpringBootTest will not start a server.
You can use the webEnvironment attribute of @SpringBootTest to further refine how your tests run:
-
MOCK(Default) : Loads a webApplicationContextand provides a mock web environment. Embedded servers are not started when using this annotation. If a web environment is not available on your classpath, this mode transparently falls back to creating a regular non-webApplicationContext. It can be used in conjunction with@AutoConfigureMockMvcor@AutoConfigureWebTestClientfor mock-based testing of your web application. -
RANDOM_PORT: Loads aWebServerApplicationContextand provides a real web environment. Embedded servers are started and listen on a random port. -
DEFINED_PORT: Loads aWebServerApplicationContextand provides a real web environment. Embedded servers are started and listen on a defined port (from yourapplication.properties) or on the default port of8080. -
NONE: Loads anApplicationContextby usingSpringApplicationbut does not provide any web environment (mock or otherwise).
If your test is @Transactional, it rolls back the transaction at the end of each test method by default.
However, as using this arrangement with either RANDOM_PORT or DEFINED_PORT implicitly provides a real servlet environment, the HTTP client and server run in separate threads and, thus, in separate transactions.
Any transaction initiated on the server does not roll back in this case.
|
@SpringBootTest with webEnvironment = WebEnvironment.RANDOM_PORT will also start the management server on a separate random port if your application uses a different port for the management server.
|
9.3.1. Detecting Web Application Type
If Spring MVC is available, a regular MVC-based application context is configured. If you have only Spring WebFlux, we will detect that and configure a WebFlux-based application context instead.
If both are present, Spring MVC takes precedence.
If you want to test a reactive web application in this scenario, you must set the spring.main.web-application-type property:
@SpringBootTest(properties = "spring.main.web-application-type=reactive")
class MyWebFluxTests {
// ...
}
@SpringBootTest(properties = ["spring.main.web-application-type=reactive"])
class MyWebFluxTests {
// ...
}
9.3.2. Detecting Test Configuration
If you are familiar with the Spring Test Framework, you may be used to using @ContextConfiguration(classes=…) in order to specify which Spring @Configuration to load.
Alternatively, you might have often used nested @Configuration classes within your test.
When testing Spring Boot applications, this is often not required.
Spring Boot’s @*Test annotations search for your primary configuration automatically whenever you do not explicitly define one.
The search algorithm works up from the package that contains the test until it finds a class annotated with @SpringBootApplication or @SpringBootConfiguration.
As long as you structured your code in a sensible way, your main configuration is usually found.
|
If you use a test annotation to test a more specific slice of your application, you should avoid adding configuration settings that are specific to a particular area on the main method’s application class. The underlying component scan configuration of |
If you want to customize the primary configuration, you can use a nested @TestConfiguration class.
Unlike a nested @Configuration class, which would be used instead of your application’s primary configuration, a nested @TestConfiguration class is used in addition to your application’s primary configuration.
| Spring’s test framework caches application contexts between tests. Therefore, as long as your tests share the same configuration (no matter how it is discovered), the potentially time-consuming process of loading the context happens only once. |
9.3.3. Using the Test Configuration Main Method
Typically the test configuration discovered by @SpringBootTest will be your main @SpringBootApplication.
In most well structured applications, this configuration class will also include the main method used to launch the application.
For example, the following is a very common code pattern for a typical Spring Boot application:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args)
}
In the example above, the main method doesn’t do anything other than delegate to SpringApplication.run.
It is, however, possible to have a more complex main method that applies customizations before calling SpringApplication.run.
For example, here is an application that changes the banner mode and sets additional profiles:
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication application = new SpringApplication(MyApplication.class);
application.setBannerMode(Banner.Mode.OFF);
application.setAdditionalProfiles("myprofile");
application.run(args);
}
}
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args) {
setBannerMode(Banner.Mode.OFF)
setAdditionalProfiles("myprofile")
}
}
Since customizations in the main method can affect the resulting ApplicationContext, it’s possible that you might also want to use the main method to create the ApplicationContext used in your tests.
By default, @SpringBootTest will not call your main method, and instead the class itself is used directly to create the ApplicationContext
If you want to change this behavior, you can change the useMainMethod attribute of @SpringBootTest to UseMainMethod.ALWAYS or UseMainMethod.WHEN_AVAILABLE.
When set to ALWAYS, the test will fail if no main method can be found.
When set to WHEN_AVAILABLE the main method will be used if it is available, otherwise the standard loading mechanism will be used.
For example, the following test will invoke the main method of MyApplication in order to create the ApplicationContext.
If the main method sets additional profiles then those will be active when the ApplicationContext starts.
@SpringBootTest(useMainMethod = UseMainMethod.ALWAYS)
class MyApplicationTests {
@Test
void exampleTest() {
// ...
}
}
@SpringBootTest(useMainMethod = UseMainMethod.ALWAYS)
class MyApplicationTests {
@Test
fun exampleTest() {
// ...
}
}
9.3.4. Excluding Test Configuration
If your application uses component scanning (for example, if you use @SpringBootApplication or @ComponentScan), you may find top-level configuration classes that you created only for specific tests accidentally get picked up everywhere.
As we have seen earlier, @TestConfiguration can be used on an inner class of a test to customize the primary configuration.
@TestConfiguration can also be used on a top-level class. Doing so indicates that the class should not be picked up by scanning.
You can then import the class explicitly where it is required, as shown in the following example:
@SpringBootTest
@Import(MyTestsConfiguration.class)
class MyTests {
@Test
void exampleTest() {
// ...
}
}
@SpringBootTest
@Import(MyTestsConfiguration::class)
class MyTests {
@Test
fun exampleTest() {
// ...
}
}
If you directly use @ComponentScan (that is, not through @SpringBootApplication) you need to register the TypeExcludeFilter with it.
See the Javadoc for details.
|
An imported @TestConfiguration is processed earlier than an inner-class @TestConfiguration and an imported @TestConfiguration will be processed before any configuration found through component scanning.
Generally speaking, this difference in ordering has no noticeable effect but it is something to be aware of if you’re relying on bean overriding.
|
9.3.5. Using Application Arguments
If your application expects arguments, you can
have @SpringBootTest inject them using the args attribute.
@SpringBootTest(args = "--app.test=one")
class MyApplicationArgumentTests {
@Test
void applicationArgumentsPopulated(@Autowired ApplicationArguments args) {
assertThat(args.getOptionNames()).containsOnly("app.test");
assertThat(args.getOptionValues("app.test")).containsOnly("one");
}
}
@SpringBootTest(args = ["--app.test=one"])
class MyApplicationArgumentTests {
@Test
fun applicationArgumentsPopulated(@Autowired args: ApplicationArguments) {
assertThat(args.optionNames).containsOnly("app.test")
assertThat(args.getOptionValues("app.test")).containsOnly("one")
}
}
9.3.6. Testing With a Mock Environment
By default, @SpringBootTest does not start the server but instead sets up a mock environment for testing web endpoints.
With Spring MVC, we can query our web endpoints using MockMvc or WebTestClient, as shown in the following example:
@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {
@Test
void testWithMockMvc(@Autowired MockMvc mvc) throws Exception {
mvc.perform(get("/")).andExpect(status().isOk()).andExpect(content().string("Hello World"));
}
// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
@Test
void testWithWebTestClient(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest
@AutoConfigureMockMvc
class MyMockMvcTests {
@Test
fun testWithMockMvc(@Autowired mvc: MockMvc) {
mvc.perform(MockMvcRequestBuilders.get("/")).andExpect(MockMvcResultMatchers.status().isOk)
.andExpect(MockMvcResultMatchers.content().string("Hello World"))
}
// If Spring WebFlux is on the classpath, you can drive MVC tests with a WebTestClient
@Test
fun testWithWebTestClient(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
If you want to focus only on the web layer and not start a complete ApplicationContext, consider using @WebMvcTest instead.
|
With Spring WebFlux endpoints, you can use WebTestClient as shown in the following example:
@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {
@Test
void exampleTest(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest
@AutoConfigureWebTestClient
class MyMockWebTestClientTests {
@Test
fun exampleTest(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
|
Testing within a mocked environment is usually faster than running with a full servlet container. However, since mocking occurs at the Spring MVC layer, code that relies on lower-level servlet container behavior cannot be directly tested with MockMvc. For example, Spring Boot’s error handling is based on the “error page” support provided by the servlet container. This means that, whilst you can test your MVC layer throws and handles exceptions as expected, you cannot directly test that a specific custom error page is rendered. If you need to test these lower-level concerns, you can start a fully running server as described in the next section. |
9.3.7. Testing With a Running Server
If you need to start a full running server, we recommend that you use random ports.
If you use @SpringBootTest(webEnvironment=WebEnvironment.RANDOM_PORT), an available port is picked at random each time your test runs.
The @LocalServerPort annotation can be used to inject the actual port used into your test.
For convenience, tests that need to make REST calls to the started server can additionally autowire a WebTestClient, which resolves relative links to the running server and comes with a dedicated API for verifying responses, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {
@Test
void exampleTest(@Autowired WebTestClient webClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Hello World");
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortWebTestClientTests {
@Test
fun exampleTest(@Autowired webClient: WebTestClient) {
webClient
.get().uri("/")
.exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Hello World")
}
}
WebTestClient can also used with a mock environment, removing the need for a running server, by annotating your test class with @AutoConfigureWebTestClient.
|
This setup requires spring-webflux on the classpath.
If you can not or will not add webflux, Spring Boot also provides a TestRestTemplate facility:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {
@Test
void exampleTest(@Autowired TestRestTemplate restTemplate) {
String body = restTemplate.getForObject("/", String.class);
assertThat(body).isEqualTo("Hello World");
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MyRandomPortTestRestTemplateTests {
@Test
fun exampleTest(@Autowired restTemplate: TestRestTemplate) {
val body = restTemplate.getForObject("/", String::class.java)
assertThat(body).isEqualTo("Hello World")
}
}
9.3.8. Customizing WebTestClient
To customize the WebTestClient bean, configure a WebTestClientBuilderCustomizer bean.
Any such beans are called with the WebTestClient.Builder that is used to create the WebTestClient.
9.3.9. Using JMX
As the test context framework caches context, JMX is disabled by default to prevent identical components to register on the same domain.
If such test needs access to an MBeanServer, consider marking it dirty as well:
@SpringBootTest(properties = "spring.jmx.enabled=true")
@DirtiesContext
class MyJmxTests {
@Autowired
private MBeanServer mBeanServer;
@Test
void exampleTest() {
assertThat(this.mBeanServer.getDomains()).contains("java.lang");
// ...
}
}
@SpringBootTest(properties = ["spring.jmx.enabled=true"])
@DirtiesContext
class MyJmxTests(@Autowired val mBeanServer: MBeanServer) {
@Test
fun exampleTest() {
assertThat(mBeanServer.domains).contains("java.lang")
// ...
}
}
9.3.10. Using Observations
If you annotate a sliced test with @AutoConfigureObservability, it auto-configures an ObservationRegistry.
9.3.11. Using Metrics
Regardless of your classpath, meter registries, except the in-memory backed, are not auto-configured when using @SpringBootTest.
If you need to export metrics to a different backend as part of an integration test, annotate it with @AutoConfigureObservability.
If you annotate a sliced test with @AutoConfigureObservability, it auto-configures an in-memory MeterRegistry.
Data exporting in sliced tests is not supported with the @AutoConfigureObservability annotation.
9.3.12. Using Tracing
Regardless of your classpath, tracing components which are reporting data are not auto-configured when using @SpringBootTest.
If you need those components as part of an integration test, annotate the test with @AutoConfigureObservability.
If you have created your own reporting components (e.g. a custom SpanExporter or SpanHandler) and you don’t want them to be active in tests, you can use the @ConditionalOnEnabledTracing annotation to disable them.
If you annotate a sliced test with @AutoConfigureObservability, it auto-configures a no-op Tracer.
Data exporting in sliced tests is not supported with the @AutoConfigureObservability annotation.
9.3.13. Mocking and Spying Beans
When running tests, it is sometimes necessary to mock certain components within your application context. For example, you may have a facade over some remote service that is unavailable during development. Mocking can also be useful when you want to simulate failures that might be hard to trigger in a real environment.
Spring Boot includes a @MockBean annotation that can be used to define a Mockito mock for a bean inside your ApplicationContext.
You can use the annotation to add new beans or replace a single existing bean definition.
The annotation can be used directly on test classes, on fields within your test, or on @Configuration classes and fields.
When used on a field, the instance of the created mock is also injected.
Mock beans are automatically reset after each test method.
|
If your test uses one of Spring Boot’s test annotations (such as Java
Kotlin
|
The following example replaces an existing RemoteService bean with a mock implementation:
@SpringBootTest
class MyTests {
@Autowired
private Reverser reverser;
@MockBean
private RemoteService remoteService;
@Test
void exampleTest() {
given(this.remoteService.getValue()).willReturn("spring");
String reverse = this.reverser.getReverseValue(); // Calls injected RemoteService
assertThat(reverse).isEqualTo("gnirps");
}
}
@SpringBootTest
class MyTests(@Autowired val reverser: Reverser, @MockBean val remoteService: RemoteService) {
@Test
fun exampleTest() {
given(remoteService.value).willReturn("spring")
val reverse = reverser.reverseValue // Calls injected RemoteService
assertThat(reverse).isEqualTo("gnirps")
}
}
@MockBean cannot be used to mock the behavior of a bean that is exercised during application context refresh.
By the time the test is executed, the application context refresh has completed and it is too late to configure the mocked behavior.
We recommend using a @Bean method to create and configure the mock in this situation.
|
Additionally, you can use @SpyBean to wrap any existing bean with a Mockito spy.
See the Javadoc for full details.
While Spring’s test framework caches application contexts between tests and reuses a context for tests sharing the same configuration, the use of @MockBean or @SpyBean influences the cache key, which will most likely increase the number of contexts.
|
If you are using @SpyBean to spy on a bean with @Cacheable methods that refer to parameters by name, your application must be compiled with -parameters.
This ensures that the parameter names are available to the caching infrastructure once the bean has been spied upon.
|
When you are using @SpyBean to spy on a bean that is proxied by Spring, you may need to remove Spring’s proxy in some situations, for example when setting expectations using given or when.
Use AopTestUtils.getTargetObject(yourProxiedSpy) to do so.
|
9.3.14. Auto-configured Tests
Spring Boot’s auto-configuration system works well for applications but can sometimes be a little too much for tests. It often helps to load only the parts of the configuration that are required to test a “slice” of your application. For example, you might want to test that Spring MVC controllers are mapping URLs correctly, and you do not want to involve database calls in those tests, or you might want to test JPA entities, and you are not interested in the web layer when those tests run.
The spring-boot-test-autoconfigure module includes a number of annotations that can be used to automatically configure such “slices”.
Each of them works in a similar way, providing a @…Test annotation that loads the ApplicationContext and one or more @AutoConfigure… annotations that can be used to customize auto-configuration settings.
Each slice restricts component scan to appropriate components and loads a very restricted set of auto-configuration classes.
If you need to exclude one of them, most @…Test annotations provide an excludeAutoConfiguration attribute.
Alternatively, you can use @ImportAutoConfiguration#exclude.
|
Including multiple “slices” by using several @…Test annotations in one test is not supported.
If you need multiple “slices”, pick one of the @…Test annotations and include the @AutoConfigure… annotations of the other “slices” by hand.
|
It is also possible to use the @AutoConfigure… annotations with the standard @SpringBootTest annotation.
You can use this combination if you are not interested in “slicing” your application but you want some of the auto-configured test beans.
|
9.3.15. Auto-configured JSON Tests
To test that object JSON serialization and deserialization is working as expected, you can use the @JsonTest annotation.
@JsonTest auto-configures the available supported JSON mapper, which can be one of the following libraries:
-
Jackson
ObjectMapper, any@JsonComponentbeans and any JacksonModules -
Gson -
Jsonb
A list of the auto-configurations that are enabled by @JsonTest can be found in the appendix.
|
If you need to configure elements of the auto-configuration, you can use the @AutoConfigureJsonTesters annotation.
Spring Boot includes AssertJ-based helpers that work with the JSONAssert and JsonPath libraries to check that JSON appears as expected.
The JacksonTester, GsonTester, JsonbTester, and BasicJsonTester classes can be used for Jackson, Gson, Jsonb, and Strings respectively.
Any helper fields on the test class can be @Autowired when using @JsonTest.
The following example shows a test class for Jackson:
@JsonTest
class MyJsonTests {
@Autowired
private JacksonTester<VehicleDetails> json;
@Test
void serialize() throws Exception {
VehicleDetails details = new VehicleDetails("Honda", "Civic");
// Assert against a `.json` file in the same package as the test
assertThat(this.json.write(details)).isEqualToJson("expected.json");
// Or use JSON path based assertions
assertThat(this.json.write(details)).hasJsonPathStringValue("@.make");
assertThat(this.json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda");
}
@Test
void deserialize() throws Exception {
String content = "{\"make\":\"Ford\",\"model\":\"Focus\"}";
assertThat(this.json.parse(content)).isEqualTo(new VehicleDetails("Ford", "Focus"));
assertThat(this.json.parseObject(content).getMake()).isEqualTo("Ford");
}
}
@JsonTest
class MyJsonTests(@Autowired val json: JacksonTester<VehicleDetails>) {
@Test
fun serialize() {
val details = VehicleDetails("Honda", "Civic")
// Assert against a `.json` file in the same package as the test
assertThat(json.write(details)).isEqualToJson("expected.json")
// Or use JSON path based assertions
assertThat(json.write(details)).hasJsonPathStringValue("@.make")
assertThat(json.write(details)).extractingJsonPathStringValue("@.make").isEqualTo("Honda")
}
@Test
fun deserialize() {
val content = "{\"make\":\"Ford\",\"model\":\"Focus\"}"
assertThat(json.parse(content)).isEqualTo(VehicleDetails("Ford", "Focus"))
assertThat(json.parseObject(content).make).isEqualTo("Ford")
}
}
JSON helper classes can also be used directly in standard unit tests.
To do so, call the initFields method of the helper in your @Before method if you do not use @JsonTest.
|
If you use Spring Boot’s AssertJ-based helpers to assert on a number value at a given JSON path, you might not be able to use isEqualTo depending on the type.
Instead, you can use AssertJ’s satisfies to assert that the value matches the given condition.
For instance, the following example asserts that the actual number is a float value close to 0.15 within an offset of 0.01.
@Test
void someTest() throws Exception {
SomeObject value = new SomeObject(0.152f);
assertThat(this.json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
.satisfies((number) -> assertThat(number.floatValue()).isCloseTo(0.15f, within(0.01f)));
}
@Test
fun someTest() {
val value = SomeObject(0.152f)
assertThat(json.write(value)).extractingJsonPathNumberValue("@.test.numberValue")
.satisfies(ThrowingConsumer { number ->
assertThat(number.toFloat()).isCloseTo(0.15f, within(0.01f))
})
}
9.3.16. Auto-configured Spring MVC Tests
To test whether Spring MVC controllers are working as expected, use the @WebMvcTest annotation.
@WebMvcTest auto-configures the Spring MVC infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, Filter, HandlerInterceptor, WebMvcConfigurer, WebMvcRegistrations, and HandlerMethodArgumentResolver.
Regular @Component and @ConfigurationProperties beans are not scanned when the @WebMvcTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configuration settings that are enabled by @WebMvcTest can be found in the appendix.
|
If you need to register extra components, such as the Jackson Module, you can import additional configuration classes by using @Import on your test.
|
Often, @WebMvcTest is limited to a single controller and is used in combination with @MockBean to provide mock implementations for required collaborators.
@WebMvcTest also auto-configures MockMvc.
Mock MVC offers a powerful way to quickly test MVC controllers without needing to start a full HTTP server.
You can also auto-configure MockMvc in a non-@WebMvcTest (such as @SpringBootTest) by annotating it with @AutoConfigureMockMvc.
The following example uses MockMvc:
|
@WebMvcTest(UserVehicleController.class)
class MyControllerTests {
@Autowired
private MockMvc mvc;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() throws Exception {
given(this.userVehicleService.getVehicleDetails("sboot"))
.willReturn(new VehicleDetails("Honda", "Civic"));
this.mvc.perform(get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
.andExpect(status().isOk())
.andExpect(content().string("Honda Civic"));
}
}
@WebMvcTest(UserVehicleController::class)
class MyControllerTests(@Autowired val mvc: MockMvc) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot"))
.willReturn(VehicleDetails("Honda", "Civic"))
mvc.perform(MockMvcRequestBuilders.get("/sboot/vehicle").accept(MediaType.TEXT_PLAIN))
.andExpect(MockMvcResultMatchers.status().isOk)
.andExpect(MockMvcResultMatchers.content().string("Honda Civic"))
}
}
If you need to configure elements of the auto-configuration (for example, when servlet filters should be applied) you can use attributes in the @AutoConfigureMockMvc annotation.
|
If you use HtmlUnit and Selenium, auto-configuration also provides an HtmlUnit WebClient bean and/or a Selenium WebDriver bean.
The following example uses HtmlUnit:
@WebMvcTest(UserVehicleController.class)
class MyHtmlUnitTests {
@Autowired
private WebClient webClient;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() throws Exception {
given(this.userVehicleService.getVehicleDetails("sboot")).willReturn(new VehicleDetails("Honda", "Civic"));
HtmlPage page = this.webClient.getPage("/sboot/vehicle.html");
assertThat(page.getBody().getTextContent()).isEqualTo("Honda Civic");
}
}
@WebMvcTest(UserVehicleController::class)
class MyHtmlUnitTests(@Autowired val webClient: WebClient) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot")).willReturn(VehicleDetails("Honda", "Civic"))
val page = webClient.getPage<HtmlPage>("/sboot/vehicle.html")
assertThat(page.body.textContent).isEqualTo("Honda Civic")
}
}
By default, Spring Boot puts WebDriver beans in a special “scope” to ensure that the driver exits after each test and that a new instance is injected.
If you do not want this behavior, you can add @Scope(ConfigurableBeanFactory.SCOPE_SINGLETON) to your WebDriver @Bean definition.
|
The webDriver scope created by Spring Boot will replace any user defined scope of the same name.
If you define your own webDriver scope you may find it stops working when you use @WebMvcTest.
|
If you have Spring Security on the classpath, @WebMvcTest will also scan WebSecurityConfigurer beans.
Instead of disabling security completely for such tests, you can use Spring Security’s test support.
More details on how to use Spring Security’s MockMvc support can be found in this howto.html how-to section.
| Sometimes writing Spring MVC tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server. |
9.3.17. Auto-configured Spring WebFlux Tests
To test that Spring WebFlux controllers are working as expected, you can use the @WebFluxTest annotation.
@WebFluxTest auto-configures the Spring WebFlux infrastructure and limits scanned beans to @Controller, @ControllerAdvice, @JsonComponent, Converter, GenericConverter, WebFilter, and WebFluxConfigurer.
Regular @Component and @ConfigurationProperties beans are not scanned when the @WebFluxTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @WebFluxTest can be found in the appendix.
|
If you need to register extra components, such as Jackson Module, you can import additional configuration classes using @Import on your test.
|
Often, @WebFluxTest is limited to a single controller and used in combination with the @MockBean annotation to provide mock implementations for required collaborators.
@WebFluxTest also auto-configures WebTestClient, which offers a powerful way to quickly test WebFlux controllers without needing to start a full HTTP server.
You can also auto-configure WebTestClient in a non-@WebFluxTest (such as @SpringBootTest) by annotating it with @AutoConfigureWebTestClient.
The following example shows a class that uses both @WebFluxTest and a WebTestClient:
|
@WebFluxTest(UserVehicleController.class)
class MyControllerTests {
@Autowired
private WebTestClient webClient;
@MockBean
private UserVehicleService userVehicleService;
@Test
void testExample() {
given(this.userVehicleService.getVehicleDetails("sboot"))
.willReturn(new VehicleDetails("Honda", "Civic"));
this.webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
.expectStatus().isOk()
.expectBody(String.class).isEqualTo("Honda Civic");
}
}
@WebFluxTest(UserVehicleController::class)
class MyControllerTests(@Autowired val webClient: WebTestClient) {
@MockBean
lateinit var userVehicleService: UserVehicleService
@Test
fun testExample() {
given(userVehicleService.getVehicleDetails("sboot"))
.willReturn(VehicleDetails("Honda", "Civic"))
webClient.get().uri("/sboot/vehicle").accept(MediaType.TEXT_PLAIN).exchange()
.expectStatus().isOk
.expectBody<String>().isEqualTo("Honda Civic")
}
}
This setup is only supported by WebFlux applications as using WebTestClient in a mocked web application only works with WebFlux at the moment.
|
@WebFluxTest cannot detect routes registered through the functional web framework.
For testing RouterFunction beans in the context, consider importing your RouterFunction yourself by using @Import or by using @SpringBootTest.
|
@WebFluxTest cannot detect custom security configuration registered as a @Bean of type SecurityWebFilterChain.
To include that in your test, you will need to import the configuration that registers the bean by using @Import or by using @SpringBootTest.
|
| Sometimes writing Spring WebFlux tests is not enough; Spring Boot can help you run full end-to-end tests with an actual server. |
9.3.18. Auto-configured Spring GraphQL Tests
Spring GraphQL offers a dedicated testing support module; you’ll need to add it to your project:
<dependencies>
<dependency>
<groupId>org.springframework.graphql</groupId>
<artifactId>spring-graphql-test</artifactId>
<scope>test</scope>
</dependency>
<!-- Unless already present in the compile scope -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
<scope>test</scope>
</dependency>
</dependencies>dependencies {
testImplementation("org.springframework.graphql:spring-graphql-test")
// Unless already present in the implementation configuration
testImplementation("org.springframework.boot:spring-boot-starter-webflux")
}This testing module ships the GraphQlTester.
The tester is heavily used in test, so be sure to become familiar with using it.
There are GraphQlTester variants and Spring Boot will auto-configure them depending on the type of tests:
-
the
ExecutionGraphQlServiceTesterperforms tests on the server side, without a client nor a transport -
the
HttpGraphQlTesterperforms tests with a client that connects to a server, with or without a live server
Spring Boot helps you to test your Spring GraphQL Controllers with the @GraphQlTest annotation.
@GraphQlTest auto-configures the Spring GraphQL infrastructure, without any transport nor server being involved.
This limits scanned beans to @Controller, RuntimeWiringConfigurer, JsonComponent, Converter, GenericConverter, DataFetcherExceptionResolver, Instrumentation and GraphQlSourceBuilderCustomizer.
Regular @Component and @ConfigurationProperties beans are not scanned when the @GraphQlTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @GraphQlTest can be found in the appendix.
|
Often, @GraphQlTest is limited to a set of controllers and used in combination with the @MockBean annotation to provide mock implementations for required collaborators.
@GraphQlTest(GreetingController.class)
class GreetingControllerTests {
@Autowired
private GraphQlTester graphQlTester;
@Test
void shouldGreetWithSpecificName() {
this.graphQlTester.document("{ greeting(name: \"Alice\") } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Alice!");
}
@Test
void shouldGreetWithDefaultName() {
this.graphQlTester.document("{ greeting } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Spring!");
}
}
@GraphQlTest(GreetingController::class)
internal class GreetingControllerTests {
@Autowired
lateinit var graphQlTester: GraphQlTester
@Test
fun shouldGreetWithSpecificName() {
graphQlTester.document("{ greeting(name: \"Alice\") } ").execute().path("greeting").entity(String::class.java)
.isEqualTo("Hello, Alice!")
}
@Test
fun shouldGreetWithDefaultName() {
graphQlTester.document("{ greeting } ").execute().path("greeting").entity(String::class.java)
.isEqualTo("Hello, Spring!")
}
}
@SpringBootTest tests are full integration tests and involve the entire application.
When using a random or defined port, a live server is configured and an HttpGraphQlTester bean is contributed automatically so you can use it to test your server.
When a MOCK environment is configured, you can also request an HttpGraphQlTester bean by annotating your test class with @AutoConfigureHttpGraphQlTester:
@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {
@Test
void shouldGreetWithSpecificName(@Autowired HttpGraphQlTester graphQlTester) {
HttpGraphQlTester authenticatedTester = graphQlTester.mutate()
.webTestClient((client) -> client.defaultHeaders((headers) -> headers.setBasicAuth("admin", "ilovespring")))
.build();
authenticatedTester.document("{ greeting(name: \"Alice\") } ")
.execute()
.path("greeting")
.entity(String.class)
.isEqualTo("Hello, Alice!");
}
}
@AutoConfigureHttpGraphQlTester
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)
class GraphQlIntegrationTests {
@Test
fun shouldGreetWithSpecificName(@Autowired graphQlTester: HttpGraphQlTester) {
val authenticatedTester = graphQlTester.mutate()
.webTestClient { client: WebTestClient.Builder ->
client.defaultHeaders { headers: HttpHeaders ->
headers.setBasicAuth("admin", "ilovespring")
}
}.build()
authenticatedTester.document("{ greeting(name: \"Alice\") } ").execute()
.path("greeting").entity(String::class.java).isEqualTo("Hello, Alice!")
}
}
9.3.19. Auto-configured Data Cassandra Tests
You can use @DataCassandraTest to test Cassandra applications.
By default, it configures a CassandraTemplate, scans for @Table classes, and configures Spring Data Cassandra repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataCassandraTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using Cassandra with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataCassandraTest can be found in the appendix.
|
The following example shows a typical setup for using Cassandra tests in Spring Boot:
@DataCassandraTest
class MyDataCassandraTests {
@Autowired
private SomeRepository repository;
}
@DataCassandraTest
class MyDataCassandraTests(@Autowired val repository: SomeRepository)
9.3.20. Auto-configured Data Couchbase Tests
You can use @DataCouchbaseTest to test Couchbase applications.
By default, it configures a CouchbaseTemplate or ReactiveCouchbaseTemplate, scans for @Document classes, and configures Spring Data Couchbase repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataCouchbaseTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using Couchbase with Spring Boot, see "data.html", earlier in this chapter.)
A list of the auto-configuration settings that are enabled by @DataCouchbaseTest can be found in the appendix.
|
The following example shows a typical setup for using Couchbase tests in Spring Boot:
@DataCouchbaseTest
class MyDataCouchbaseTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataCouchbaseTest
class MyDataCouchbaseTests(@Autowired val repository: SomeRepository) {
// ...
}
9.3.21. Auto-configured Data Elasticsearch Tests
You can use @DataElasticsearchTest to test Elasticsearch applications.
By default, it configures an ElasticsearchRestTemplate, scans for @Document classes, and configures Spring Data Elasticsearch repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataElasticsearchTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using Elasticsearch with Spring Boot, see "data.html", earlier in this chapter.)
A list of the auto-configuration settings that are enabled by @DataElasticsearchTest can be found in the appendix.
|
The following example shows a typical setup for using Elasticsearch tests in Spring Boot:
@DataElasticsearchTest
class MyDataElasticsearchTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataElasticsearchTest
class MyDataElasticsearchTests(@Autowired val repository: SomeRepository) {
// ...
}
9.3.22. Auto-configured Data JPA Tests
You can use the @DataJpaTest annotation to test JPA applications.
By default, it scans for @Entity classes and configures Spring Data JPA repositories.
If an embedded database is available on the classpath, it configures one as well.
SQL queries are logged by default by setting the spring.jpa.show-sql property to true.
This can be disabled using the showSql attribute of the annotation.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataJpaTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configuration settings that are enabled by @DataJpaTest can be found in the appendix.
|
By default, data JPA tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class as follows:
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {
// ...
}
@DataJpaTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyNonTransactionalTests {
// ...
}
Data JPA tests may also inject a TestEntityManager bean, which provides an alternative to the standard JPA EntityManager that is specifically designed for tests.
TestEntityManager can also be auto-configured to any of your Spring-based test class by adding @AutoConfigureTestEntityManager.
When doing so, make sure that your test is running in a transaction, for instance by adding @Transactional on your test class or method.
|
A JdbcTemplate is also available if you need that.
The following example shows the @DataJpaTest annotation in use:
@DataJpaTest
class MyRepositoryTests {
@Autowired
private TestEntityManager entityManager;
@Autowired
private UserRepository repository;
@Test
void testExample() {
this.entityManager.persist(new User("sboot", "1234"));
User user = this.repository.findByUsername("sboot");
assertThat(user.getUsername()).isEqualTo("sboot");
assertThat(user.getEmployeeNumber()).isEqualTo("1234");
}
}
@DataJpaTest
class MyRepositoryTests(@Autowired val entityManager: TestEntityManager, @Autowired val repository: UserRepository) {
@Test
fun testExample() {
entityManager.persist(User("sboot", "1234"))
val user = repository.findByUsername("sboot")
assertThat(user?.username).isEqualTo("sboot")
assertThat(user?.employeeNumber).isEqualTo("1234")
}
}
In-memory embedded databases generally work well for tests, since they are fast and do not require any installation.
If, however, you prefer to run tests against a real database you can use the @AutoConfigureTestDatabase annotation, as shown in the following example:
@DataJpaTest
@AutoConfigureTestDatabase(replace = Replace.NONE)
class MyRepositoryTests {
// ...
}
@DataJpaTest
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
class MyRepositoryTests {
// ...
}
9.3.23. Auto-configured JDBC Tests
@JdbcTest is similar to @DataJpaTest but is for tests that only require a DataSource and do not use Spring Data JDBC.
By default, it configures an in-memory embedded database and a JdbcTemplate.
Regular @Component and @ConfigurationProperties beans are not scanned when the @JdbcTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @JdbcTest can be found in the appendix.
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By default, JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests {
}
@JdbcTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyTransactionalTests
If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest.
(See "Auto-configured Data JPA Tests".)
9.3.24. Auto-configured Data JDBC Tests
@DataJdbcTest is similar to @JdbcTest but is for tests that use Spring Data JDBC repositories.
By default, it configures an in-memory embedded database, a JdbcTemplate, and Spring Data JDBC repositories.
Only AbstractJdbcConfiguration subclasses are scanned when the @DataJdbcTest annotation is used, regular @Component and @ConfigurationProperties beans are not scanned.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @DataJdbcTest can be found in the appendix.
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By default, Data JDBC tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.
If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest.
(See "Auto-configured Data JPA Tests".)
9.3.25. Auto-configured Data R2DBC Tests
@DataR2dbcTest is similar to @DataJdbcTest but is for tests that use Spring Data R2DBC repositories.
By default, it configures an in-memory embedded database, an R2dbcEntityTemplate, and Spring Data R2DBC repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataR2dbcTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @DataR2dbcTest can be found in the appendix.
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By default, Data R2DBC tests are not transactional.
If you prefer your test to run against a real database, you can use the @AutoConfigureTestDatabase annotation in the same way as for @DataJpaTest.
(See "Auto-configured Data JPA Tests".)
9.3.26. Auto-configured jOOQ Tests
You can use @JooqTest in a similar fashion as @JdbcTest but for jOOQ-related tests.
As jOOQ relies heavily on a Java-based schema that corresponds with the database schema, the existing DataSource is used.
If you want to replace it with an in-memory database, you can use @AutoConfigureTestDatabase to override those settings.
(For more about using jOOQ with Spring Boot, see "data.html".)
Regular @Component and @ConfigurationProperties beans are not scanned when the @JooqTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configurations that are enabled by @JooqTest can be found in the appendix.
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@JooqTest configures a DSLContext.
The following example shows the @JooqTest annotation in use:
@JooqTest
class MyJooqTests {
@Autowired
private DSLContext dslContext;
// ...
}
@JooqTest
class MyJooqTests(@Autowired val dslContext: DSLContext) {
// ...
}
JOOQ tests are transactional and roll back at the end of each test by default. If that is not what you want, you can disable transaction management for a test or for the whole test class as shown in the JDBC example.
9.3.27. Auto-configured Data MongoDB Tests
You can use @DataMongoTest to test MongoDB applications.
By default, it configures a MongoTemplate, scans for @Document classes, and configures Spring Data MongoDB repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataMongoTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using MongoDB with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataMongoTest can be found in the appendix.
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The following class shows the @DataMongoTest annotation in use:
@DataMongoTest
class MyDataMongoDbTests {
@Autowired
private MongoTemplate mongoTemplate;
// ...
}
@DataMongoTest
class MyDataMongoDbTests(@Autowired val mongoTemplate: MongoTemplate) {
// ...
}
9.3.28. Auto-configured Data Neo4j Tests
You can use @DataNeo4jTest to test Neo4j applications.
By default, it scans for @Node classes, and configures Spring Data Neo4j repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataNeo4jTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using Neo4J with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataNeo4jTest can be found in the appendix.
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The following example shows a typical setup for using Neo4J tests in Spring Boot:
@DataNeo4jTest
class MyDataNeo4jTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataNeo4jTest
class MyDataNeo4jTests(@Autowired val repository: SomeRepository) {
// ...
}
By default, Data Neo4j tests are transactional and roll back at the end of each test. See the relevant section in the Spring Framework Reference Documentation for more details. If that is not what you want, you can disable transaction management for a test or for the whole class, as follows:
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests {
}
@DataNeo4jTest
@Transactional(propagation = Propagation.NOT_SUPPORTED)
class MyDataNeo4jTests
Transactional tests are not supported with reactive access.
If you are using this style, you must configure @DataNeo4jTest tests as described above.
|
9.3.29. Auto-configured Data Redis Tests
You can use @DataRedisTest to test Redis applications.
By default, it scans for @RedisHash classes and configures Spring Data Redis repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataRedisTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using Redis with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataRedisTest can be found in the appendix.
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The following example shows the @DataRedisTest annotation in use:
@DataRedisTest
class MyDataRedisTests {
@Autowired
private SomeRepository repository;
// ...
}
@DataRedisTest
class MyDataRedisTests(@Autowired val repository: SomeRepository) {
// ...
}
9.3.30. Auto-configured Data LDAP Tests
You can use @DataLdapTest to test LDAP applications.
By default, it configures an in-memory embedded LDAP (if available), configures an LdapTemplate, scans for @Entry classes, and configures Spring Data LDAP repositories.
Regular @Component and @ConfigurationProperties beans are not scanned when the @DataLdapTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
(For more about using LDAP with Spring Boot, see "data.html".)
A list of the auto-configuration settings that are enabled by @DataLdapTest can be found in the appendix.
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The following example shows the @DataLdapTest annotation in use:
@DataLdapTest
class MyDataLdapTests {
@Autowired
private LdapTemplate ldapTemplate;
// ...
}
@DataLdapTest
class MyDataLdapTests(@Autowired val ldapTemplate: LdapTemplate) {
// ...
}
In-memory embedded LDAP generally works well for tests, since it is fast and does not require any developer installation. If, however, you prefer to run tests against a real LDAP server, you should exclude the embedded LDAP auto-configuration, as shown in the following example:
@DataLdapTest(excludeAutoConfiguration = EmbeddedLdapAutoConfiguration.class)
class MyDataLdapTests {
// ...
}
@DataLdapTest(excludeAutoConfiguration = [EmbeddedLdapAutoConfiguration::class])
class MyDataLdapTests {
// ...
}
9.3.31. Auto-configured REST Clients
You can use the @RestClientTest annotation to test REST clients.
By default, it auto-configures Jackson, GSON, and Jsonb support, configures a RestTemplateBuilder and a RestClient.Builder, and adds support for MockRestServiceServer.
Regular @Component and @ConfigurationProperties beans are not scanned when the @RestClientTest annotation is used.
@EnableConfigurationProperties can be used to include @ConfigurationProperties beans.
A list of the auto-configuration settings that are enabled by @RestClientTest can be found in the appendix.
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The specific beans that you want to test should be specified by using the value or components attribute of @RestClientTest.
When using a RestTemplateBuilder in the beans under test and RestTemplateBuilder.rootUri(String rootUri) has been called when building the RestTemplate, then the root URI should be omitted from the MockRestServiceServer expectations as shown in the following example:
@RestClientTest(RemoteVehicleDetailsService.class)
class MyRestTemplateServiceTests {
@Autowired
private RemoteVehicleDetailsService service;
@Autowired
private MockRestServiceServer server;
@Test
void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
this.server.expect(requestTo("/greet/details")).andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
String greeting = this.service.callRestService();
assertThat(greeting).isEqualTo("hello");
}
}
@RestClientTest(RemoteVehicleDetailsService::class)
class MyRestTemplateServiceTests(
@Autowired val service: RemoteVehicleDetailsService,
@Autowired val server: MockRestServiceServer) {
@Test
fun getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
server.expect(MockRestRequestMatchers.requestTo("/greet/details"))
.andRespond(MockRestResponseCreators.withSuccess("hello", MediaType.TEXT_PLAIN))
val greeting = service.callRestService()
assertThat(greeting).isEqualTo("hello")
}
}
When using a RestClient.Builder in the beans under test, or when using a RestTemplateBuilder without calling rootUri(String rootURI), the full URI must be used in the MockRestServiceServer expectations as shown in the following example:
@RestClientTest(RemoteVehicleDetailsService.class)
class MyRestClientServiceTests {
@Autowired
private RemoteVehicleDetailsService service;
@Autowired
private MockRestServiceServer server;
@Test
void getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
this.server.expect(requestTo("https://example.com/greet/details"))
.andRespond(withSuccess("hello", MediaType.TEXT_PLAIN));
String greeting = this.service.callRestService();
assertThat(greeting).isEqualTo("hello");
}
}
@RestClientTest(RemoteVehicleDetailsService::class)
class MyRestClientServiceTests(
@Autowired val service: RemoteVehicleDetailsService,
@Autowired val server: MockRestServiceServer) {
@Test
fun getVehicleDetailsWhenResultIsSuccessShouldReturnDetails() {
server.expect(MockRestRequestMatchers.requestTo("https://example.com/greet/details"))
.andRespond(MockRestResponseCreators.withSuccess("hello", MediaType.TEXT_PLAIN))
val greeting = service.callRestService()
assertThat(greeting).isEqualTo("hello")
}
}
9.3.32. Auto-configured Spring REST Docs Tests
You can use the @AutoConfigureRestDocs annotation to use Spring REST Docs in your tests with Mock MVC, REST Assured, or WebTestClient.
It removes the need for the JUnit extension in Spring REST Docs.
@AutoConfigureRestDocs can be used to override the default output directory (target/generated-snippets if you are using Maven or build/generated-snippets if you are using Gradle).
It can also be used to configure the host, scheme, and port that appears in any documented URIs.
Auto-configured Spring REST Docs Tests With Mock MVC
@AutoConfigureRestDocs customizes the MockMvc bean to use Spring REST Docs when testing servlet-based web applications.
You can inject it by using @Autowired and use it in your tests as you normally would when using Mock MVC and Spring REST Docs, as shown in the following example:
@WebMvcTest(UserController.class)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Autowired
private MockMvc mvc;
@Test
void listUsers() throws Exception {
this.mvc.perform(get("/users").accept(MediaType.TEXT_PLAIN))
.andExpect(status().isOk())
.andDo(document("list-users"));
}
}
@WebMvcTest(UserController::class)
@AutoConfigureRestDocs
class MyUserDocumentationTests(@Autowired val mvc: MockMvc) {
@Test
fun listUsers() {
mvc.perform(MockMvcRequestBuilders.get("/users").accept(MediaType.TEXT_PLAIN))
.andExpect(MockMvcResultMatchers.status().isOk)
.andDo(MockMvcRestDocumentation.document("list-users"))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, you can use a RestDocsMockMvcConfigurationCustomizer bean, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsMockMvcConfigurationCustomizer {
@Override
public void customize(MockMvcRestDocumentationConfigurer configurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsMockMvcConfigurationCustomizer {
override fun customize(configurer: MockMvcRestDocumentationConfigurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
}
}
If you want to make use of Spring REST Docs support for a parameterized output directory, you can create a RestDocumentationResultHandler bean.
The auto-configuration calls alwaysDo with this result handler, thereby causing each MockMvc call to automatically generate the default snippets.
The following example shows a RestDocumentationResultHandler being defined:
@TestConfiguration(proxyBeanMethods = false)
public class MyResultHandlerConfiguration {
@Bean
public RestDocumentationResultHandler restDocumentation() {
return MockMvcRestDocumentation.document("{method-name}");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyResultHandlerConfiguration {
@Bean
fun restDocumentation(): RestDocumentationResultHandler {
return MockMvcRestDocumentation.document("{method-name}")
}
}
Auto-configured Spring REST Docs Tests With WebTestClient
@AutoConfigureRestDocs can also be used with WebTestClient when testing reactive web applications.
You can inject it by using @Autowired and use it in your tests as you normally would when using @WebFluxTest and Spring REST Docs, as shown in the following example:
@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests {
@Autowired
private WebTestClient webTestClient;
@Test
void listUsers() {
this.webTestClient
.get().uri("/")
.exchange()
.expectStatus()
.isOk()
.expectBody()
.consumeWith(document("list-users"));
}
}
@WebFluxTest
@AutoConfigureRestDocs
class MyUsersDocumentationTests(@Autowired val webTestClient: WebTestClient) {
@Test
fun listUsers() {
webTestClient
.get().uri("/")
.exchange()
.expectStatus()
.isOk
.expectBody()
.consumeWith(WebTestClientRestDocumentation.document("list-users"))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, you can use a RestDocsWebTestClientConfigurationCustomizer bean, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsWebTestClientConfigurationCustomizer {
@Override
public void customize(WebTestClientRestDocumentationConfigurer configurer) {
configurer.snippets().withEncoding("UTF-8");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsWebTestClientConfigurationCustomizer {
override fun customize(configurer: WebTestClientRestDocumentationConfigurer) {
configurer.snippets().withEncoding("UTF-8")
}
}
If you want to make use of Spring REST Docs support for a parameterized output directory, you can use a WebTestClientBuilderCustomizer to configure a consumer for every entity exchange result.
The following example shows such a WebTestClientBuilderCustomizer being defined:
@TestConfiguration(proxyBeanMethods = false)
public class MyWebTestClientBuilderCustomizerConfiguration {
@Bean
public WebTestClientBuilderCustomizer restDocumentation() {
return (builder) -> builder.entityExchangeResultConsumer(document("{method-name}"));
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyWebTestClientBuilderCustomizerConfiguration {
@Bean
fun restDocumentation(): WebTestClientBuilderCustomizer {
return WebTestClientBuilderCustomizer { builder: WebTestClient.Builder ->
builder.entityExchangeResultConsumer(
WebTestClientRestDocumentation.document("{method-name}")
)
}
}
}
Auto-configured Spring REST Docs Tests With REST Assured
@AutoConfigureRestDocs makes a RequestSpecification bean, preconfigured to use Spring REST Docs, available to your tests.
You can inject it by using @Autowired and use it in your tests as you normally would when using REST Assured and Spring REST Docs, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Test
void listUsers(@Autowired RequestSpecification documentationSpec, @LocalServerPort int port) {
given(documentationSpec)
.filter(document("list-users"))
.when()
.port(port)
.get("/")
.then().assertThat()
.statusCode(is(200));
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@AutoConfigureRestDocs
class MyUserDocumentationTests {
@Test
fun listUsers(@Autowired documentationSpec: RequestSpecification?, @LocalServerPort port: Int) {
RestAssured.given(documentationSpec)
.filter(RestAssuredRestDocumentation.document("list-users"))
.`when`()
.port(port)["/"]
.then().assertThat()
.statusCode(Matchers.`is`(200))
}
}
If you require more control over Spring REST Docs configuration than offered by the attributes of @AutoConfigureRestDocs, a RestDocsRestAssuredConfigurationCustomizer bean can be used, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRestDocsConfiguration implements RestDocsRestAssuredConfigurationCustomizer {
@Override
public void customize(RestAssuredRestDocumentationConfigurer configurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown());
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRestDocsConfiguration : RestDocsRestAssuredConfigurationCustomizer {
override fun customize(configurer: RestAssuredRestDocumentationConfigurer) {
configurer.snippets().withTemplateFormat(TemplateFormats.markdown())
}
}
9.3.33. Auto-configured Spring Web Services Tests
Auto-configured Spring Web Services Client Tests
You can use @WebServiceClientTest to test applications that call web services using the Spring Web Services project.
By default, it configures a mock WebServiceServer bean and automatically customizes your WebServiceTemplateBuilder.
(For more about using Web Services with Spring Boot, see "io.html".)
A list of the auto-configuration settings that are enabled by @WebServiceClientTest can be found in the appendix.
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The following example shows the @WebServiceClientTest annotation in use:
@WebServiceClientTest(SomeWebService.class)
class MyWebServiceClientTests {
@Autowired
private MockWebServiceServer server;
@Autowired
private SomeWebService someWebService;
@Test
void mockServerCall() {
this.server
.expect(payload(new StringSource("<request/>")))
.andRespond(withPayload(new StringSource("<response><status>200</status></response>")));
assertThat(this.someWebService.test())
.extracting(Response::getStatus)
.isEqualTo(200);
}
}
@WebServiceClientTest(SomeWebService::class)
class MyWebServiceClientTests(@Autowired val server: MockWebServiceServer, @Autowired val someWebService: SomeWebService) {
@Test
fun mockServerCall() {
server
.expect(RequestMatchers.payload(StringSource("<request/>")))
.andRespond(ResponseCreators.withPayload(StringSource("<response><status>200</status></response>")))
assertThat(this.someWebService.test()).extracting(Response::status).isEqualTo(200)
}
}
Auto-configured Spring Web Services Server Tests
You can use @WebServiceServerTest to test applications that implement web services using the Spring Web Services project.
By default, it configures a MockWebServiceClient bean that can be used to call your web service endpoints.
(For more about using Web Services with Spring Boot, see "io.html".)
A list of the auto-configuration settings that are enabled by @WebServiceServerTest can be found in the appendix.
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The following example shows the @WebServiceServerTest annotation in use:
@WebServiceServerTest(ExampleEndpoint.class)
class MyWebServiceServerTests {
@Autowired
private MockWebServiceClient client;
@Test
void mockServerCall() {
this.client
.sendRequest(RequestCreators.withPayload(new StringSource("<ExampleRequest/>")))
.andExpect(ResponseMatchers.payload(new StringSource("<ExampleResponse>42</ExampleResponse>")));
}
}
@WebServiceServerTest(ExampleEndpoint::class)
class MyWebServiceServerTests(@Autowired val client: MockWebServiceClient) {
@Test
fun mockServerCall() {
client
.sendRequest(RequestCreators.withPayload(StringSource("<ExampleRequest/>")))
.andExpect(ResponseMatchers.payload(StringSource("<ExampleResponse>42</ExampleResponse>")))
}
}
9.3.34. Additional Auto-configuration and Slicing
Each slice provides one or more @AutoConfigure… annotations that namely defines the auto-configurations that should be included as part of a slice.
Additional auto-configurations can be added on a test-by-test basis by creating a custom @AutoConfigure… annotation or by adding @ImportAutoConfiguration to the test as shown in the following example:
@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration.class)
class MyJdbcTests {
}
@JdbcTest
@ImportAutoConfiguration(IntegrationAutoConfiguration::class)
class MyJdbcTests
Make sure to not use the regular @Import annotation to import auto-configurations as they are handled in a specific way by Spring Boot.
|
Alternatively, additional auto-configurations can be added for any use of a slice annotation by registering them in a file stored in META-INF/spring as shown in the following example:
com.example.IntegrationAutoConfiguration
In this example, the com.example.IntegrationAutoConfiguration is enabled on every test annotated with @JdbcTest.
You can use comments with # in this file.
|
A slice or @AutoConfigure… annotation can be customized this way as long as it is meta-annotated with @ImportAutoConfiguration.
|
9.3.35. User Configuration and Slicing
If you structure your code in a sensible way, your @SpringBootApplication class is used by default as the configuration of your tests.
It then becomes important not to litter the application’s main class with configuration settings that are specific to a particular area of its functionality.
Assume that you are using Spring Data MongoDB, you rely on the auto-configuration for it, and you have enabled auditing.
You could define your @SpringBootApplication as follows:
@SpringBootApplication
@EnableMongoAuditing
public class MyApplication {
// ...
}
@SpringBootApplication
@EnableMongoAuditing
class MyApplication {
// ...
}
Because this class is the source configuration for the test, any slice test actually tries to enable Mongo auditing, which is definitely not what you want to do.
A recommended approach is to move that area-specific configuration to a separate @Configuration class at the same level as your application, as shown in the following example:
@Configuration(proxyBeanMethods = false)
@EnableMongoAuditing
public class MyMongoConfiguration {
// ...
}
@Configuration(proxyBeanMethods = false)
@EnableMongoAuditing
class MyMongoConfiguration {
// ...
}
Depending on the complexity of your application, you may either have a single @Configuration class for your customizations or one class per domain area.
The latter approach lets you enable it in one of your tests, if necessary, with the @Import annotation.
See this how-to section for more details on when you might want to enable specific @Configuration classes for slice tests.
|
Test slices exclude @Configuration classes from scanning.
For example, for a @WebMvcTest, the following configuration will not include the given WebMvcConfigurer bean in the application context loaded by the test slice:
@Configuration(proxyBeanMethods = false)
public class MyWebConfiguration {
@Bean
public WebMvcConfigurer testConfigurer() {
return new WebMvcConfigurer() {
// ...
};
}
}
@Configuration(proxyBeanMethods = false)
class MyWebConfiguration {
@Bean
fun testConfigurer(): WebMvcConfigurer {
return object : WebMvcConfigurer {
// ...
}
}
}
The configuration below will, however, cause the custom WebMvcConfigurer to be loaded by the test slice.
@Component
public class MyWebMvcConfigurer implements WebMvcConfigurer {
// ...
}
@Component
class MyWebMvcConfigurer : WebMvcConfigurer {
// ...
}
Another source of confusion is classpath scanning. Assume that, while you structured your code in a sensible way, you need to scan an additional package. Your application may resemble the following code:
@SpringBootApplication
@ComponentScan({ "com.example.app", "com.example.another" })
public class MyApplication {
// ...
}
@SpringBootApplication
@ComponentScan("com.example.app", "com.example.another")
class MyApplication {
// ...
}
Doing so effectively overrides the default component scan directive with the side effect of scanning those two packages regardless of the slice that you chose.
For instance, a @DataJpaTest seems to suddenly scan components and user configurations of your application.
Again, moving the custom directive to a separate class is a good way to fix this issue.
If this is not an option for you, you can create a @SpringBootConfiguration somewhere in the hierarchy of your test so that it is used instead.
Alternatively, you can specify a source for your test, which disables the behavior of finding a default one.
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9.3.36. Using Spock to Test Spring Boot Applications
Spock 2.2 or later can be used to test a Spring Boot application.
To do so, add a dependency on a -groovy-4.0 version of Spock’s spock-spring module to your application’s build.
spock-spring integrates Spring’s test framework into Spock.
See the documentation for Spock’s Spring module for further details.
9.4. Testcontainers
The Testcontainers library provides a way to manage services running inside Docker containers. It integrates with JUnit, allowing you to write a test class that can start up a container before any of the tests run. Testcontainers is especially useful for writing integration tests that talk to a real backend service such as MySQL, MongoDB, Cassandra and others.
Testcontainers can be used in a Spring Boot test as follows:
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Container
static Neo4jContainer<?> neo4j = new Neo4jContainer<>("neo4j:5");
@Test
void myTest() {
// ...
}
}
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Test
fun myTest() {
// ...
}
companion object {
@Container
val neo4j = Neo4jContainer("neo4j:5")
}
}
This will start up a docker container running Neo4j (if Docker is running locally) before any of the tests are run. In most cases, you will need to configure the application to connect to the service running in the container.
9.4.1. Service Connections
A service connection is a connection to any remote service. Spring Boot’s auto-configuration can consume the details of a service connection and use them to establish a connection to a remote service. When doing so, the connection details take precedence over any connection-related configuration properties.
When using Testcontainers, connection details can be automatically created for a service running in a container by annotating the container field in the test class.
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Container
@ServiceConnection
static Neo4jContainer<?> neo4j = new Neo4jContainer<>("neo4j:5");
@Test
void myTest() {
// ...
}
}
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Test
fun myTest() {
// ...
}
companion object {
@Container
@ServiceConnection
val neo4j = Neo4jContainer("neo4j:5")
}
}
Thanks to @ServiceConnection, the above configuration allows Neo4j-related beans in the application to communicate with Neo4j running inside the Testcontainers-managed Docker container.
This is done by automatically defining a Neo4jConnectionDetails bean which is then used by the Neo4j auto-configuration, overriding any connection-related configuration properties.
You’ll need to add the spring-boot-testcontainers module as a test dependency in order to use service connections with Testcontainers.
|
Service connection annotations are processed by ContainerConnectionDetailsFactory classes registered with spring.factories.
A ContainerConnectionDetailsFactory can create a ConnectionDetails bean based on a specific Container subclass, or the Docker image name.
The following service connection factories are provided in the spring-boot-testcontainers jar:
| Connection Details | Matched on |
|---|---|
|
Containers named "symptoma/activemq" |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers named "otel/opentelemetry-collector-contrib" |
|
Containers named "otel/opentelemetry-collector-contrib" |
|
Containers of type |
|
Containers of type |
|
Containers of type |
|
Containers named "redis" |
|
Containers named "openzipkin/zipkin" |
|
By default all applicable connection details beans will be created for a given If you want to create only a subset of the applicable types, you can use the |
By default Container.getDockerImageName().getRepository() is used to obtain the name used to find connection details.
The repository portion of the Docker image name ignores any registry and the version.
This works as long as Spring Boot is able to get the instance of the Container, which is the case when using a static field like in the example above.
If you’re using a @Bean method, Spring Boot won’t call the bean method to get the Docker image name, because this would cause eager initialization issues.
Instead, the return type of the bean method is used to find out which connection detail should be used.
This works as long as you’re using typed containers, e.g. Neo4jContainer or RabbitMQContainer.
This stops working if you’re using GenericContainer, e.g. with Redis, as shown in the following example:
@TestConfiguration(proxyBeanMethods = false)
public class MyRedisConfiguration {
@Bean
@ServiceConnection(name = "redis")
public GenericContainer<?> redisContainer() {
return new GenericContainer<>("redis:7");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyRedisConfiguration {
@Bean
@ServiceConnection(name = "redis")
fun redisContainer(): GenericContainer<*> {
return GenericContainer("redis:7")
}
}
Spring Boot can’t tell from GenericContainer which container image is used, so the name attribute from @ServiceConnection must be used to provide that hint.
You can also can use the name attribute of @ServiceConnection to override which connection detail will be used, for example when using custom images.
If you are using the Docker image registry.mycompany.com/mirror/myredis, you’d use @ServiceConnection(name="redis") to ensure RedisConnectionDetails are created.
9.4.2. Dynamic Properties
A slightly more verbose but also more flexible alternative to service connections is @DynamicPropertySource.
A static @DynamicPropertySource method allows adding dynamic property values to the Spring Environment.
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Container
static Neo4jContainer<?> neo4j = new Neo4jContainer<>("neo4j:5");
@Test
void myTest() {
// ...
}
@DynamicPropertySource
static void neo4jProperties(DynamicPropertyRegistry registry) {
registry.add("spring.neo4j.uri", neo4j::getBoltUrl);
}
}
@Testcontainers
@SpringBootTest
class MyIntegrationTests {
@Test
fun myTest() {
// ...
}
companion object {
@Container
val neo4j = Neo4jContainer("neo4j:5")
@DynamicPropertySource
fun neo4jProperties(registry: DynamicPropertyRegistry) {
registry.add("spring.neo4j.uri") { neo4j.boltUrl }
}
}
}
The above configuration allows Neo4j-related beans in the application to communicate with Neo4j running inside the Testcontainers-managed Docker container.
9.5. Test Utilities
A few test utility classes that are generally useful when testing your application are packaged as part of spring-boot.
9.5.1. ConfigDataApplicationContextInitializer
ConfigDataApplicationContextInitializer is an ApplicationContextInitializer that you can apply to your tests to load Spring Boot application.properties files.
You can use it when you do not need the full set of features provided by @SpringBootTest, as shown in the following example:
@ContextConfiguration(classes = Config.class, initializers = ConfigDataApplicationContextInitializer.class)
class MyConfigFileTests {
// ...
}
@ContextConfiguration(classes = [Config::class], initializers = [ConfigDataApplicationContextInitializer::class])
class MyConfigFileTests {
// ...
}
Using ConfigDataApplicationContextInitializer alone does not provide support for @Value("${…}") injection.
Its only job is to ensure that application.properties files are loaded into Spring’s Environment.
For @Value support, you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest, which auto-configures one for you.
|
9.5.2. TestPropertyValues
TestPropertyValues lets you quickly add properties to a ConfigurableEnvironment or ConfigurableApplicationContext.
You can call it with key=value strings, as follows:
class MyEnvironmentTests {
@Test
void testPropertySources() {
MockEnvironment environment = new MockEnvironment();
TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment);
assertThat(environment.getProperty("name")).isEqualTo("Boot");
}
}
class MyEnvironmentTests {
@Test
fun testPropertySources() {
val environment = MockEnvironment()
TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment)
assertThat(environment.getProperty("name")).isEqualTo("Boot")
}
}
9.5.3. OutputCapture
OutputCapture is a JUnit Extension that you can use to capture System.out and System.err output.
To use it, add @ExtendWith(OutputCaptureExtension.class) and inject CapturedOutput as an argument to your test class constructor or test method as follows:
@ExtendWith(OutputCaptureExtension.class)
class MyOutputCaptureTests {
@Test
void testName(CapturedOutput output) {
System.out.println("Hello World!");
assertThat(output).contains("World");
}
}
@ExtendWith(OutputCaptureExtension::class)
class MyOutputCaptureTests {
@Test
fun testName(output: CapturedOutput?) {
println("Hello World!")
assertThat(output).contains("World")
}
}
9.5.4. TestRestTemplate
TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful in integration tests.
You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password).
In either case, the template is fault tolerant.
This means that it behaves in a test-friendly way by not throwing exceptions on 4xx and 5xx errors.
Instead, such errors can be detected through the returned ResponseEntity and its status code.
Spring Framework 5.0 provides a new WebTestClient that works for WebFlux integration tests and both WebFlux and MVC end-to-end testing.
It provides a fluent API for assertions, unlike TestRestTemplate.
|
It is recommended, but not mandatory, to use the Apache HTTP Client (version 5.1 or better).
If you have that on your classpath, the TestRestTemplate responds by configuring the client appropriately.
If you do use Apache’s HTTP client, some additional test-friendly features are enabled:
-
Redirects are not followed (so you can assert the response location).
-
Cookies are ignored (so the template is stateless).
TestRestTemplate can be instantiated directly in your integration tests, as shown in the following example:
class MyTests {
private final TestRestTemplate template = new TestRestTemplate();
@Test
void testRequest() {
ResponseEntity<String> headers = this.template.getForEntity("https://myhost.example.com/example", String.class);
assertThat(headers.getHeaders().getLocation()).hasHost("other.example.com");
}
}
class MyTests {
private val template = TestRestTemplate()
@Test
fun testRequest() {
val headers = template.getForEntity("https://myhost.example.com/example", String::class.java)
assertThat(headers.headers.location).hasHost("other.example.com")
}
}
Alternatively, if you use the @SpringBootTest annotation with WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can inject a fully configured TestRestTemplate and start using it.
If necessary, additional customizations can be applied through the RestTemplateBuilder bean.
Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests {
@Autowired
private TestRestTemplate template;
@Test
void testRequest() {
HttpHeaders headers = this.template.getForEntity("/example", String.class).getHeaders();
assertThat(headers.getLocation()).hasHost("other.example.com");
}
@TestConfiguration(proxyBeanMethods = false)
static class RestTemplateBuilderConfiguration {
@Bean
RestTemplateBuilder restTemplateBuilder() {
return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
.setReadTimeout(Duration.ofSeconds(1));
}
}
}
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests(@Autowired val template: TestRestTemplate) {
@Test
fun testRequest() {
val headers = template.getForEntity("/example", String::class.java).headers
assertThat(headers.location).hasHost("other.example.com")
}
@TestConfiguration(proxyBeanMethods = false)
internal class RestTemplateBuilderConfiguration {
@Bean
fun restTemplateBuilder(): RestTemplateBuilder {
return RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
.setReadTimeout(Duration.ofSeconds(1))
}
}
}
10. Docker Compose Support
Docker Compose is a popular technology that can be used to define and manage multiple containers for services that your application needs.
A compose.yml file is typically created next to your application which defines and configures service containers.
A typical workflow with Docker Compose is to run docker compose up, work on your application with it connecting to started services, then run docker compose down when you are finished.
The spring-boot-docker-compose module can be included in a project to provide support for working with containers using Docker Compose.
Add the module dependency to your build, as shown in the following listings for Maven and Gradle:
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-docker-compose</artifactId>
<optional>true</optional>
</dependency>
</dependencies>dependencies {
developmentOnly("org.springframework.boot:spring-boot-docker-compose")
}When this module is included as a dependency Spring Boot will do the following:
-
Search for a
compose.ymland other common compose filenames in your working directory -
Call
docker compose upwith the discoveredcompose.yml -
Create service connection beans for each supported container
-
Call
docker compose stopwhen the application is shutdown
If the Docker Compose services are already running when starting the application, Spring Boot will only create the service connection beans for each supported container.
It will not call docker compose up again and it will not call docker compose stop when the application is shutdown.
Repackaged archives do not contain Spring Boot’s Docker Compose by default.
If you want to use this support, you need to include it.
When using the Maven plugin, set the excludeDockerCompose property to false.
When using the Gradle plugin, configure the task’s classpath to include the developmentOnly configuration.
|
10.1. Prerequisites
You need to have the docker and docker compose (or docker-compose) CLI applications on your path.
The minimum supported Docker Compose version is 2.2.0.
10.2. Service Connections
A service connection is a connection to any remote service. Spring Boot’s auto-configuration can consume the details of a service connection and use them to establish a connection to a remote service. When doing so, the connection details take precedence over any connection-related configuration properties.
When using Spring Boot’s Docker Compose support, service connections are established to the port mapped by the container.
| Docker compose is usually used in such a way that the ports inside the container are mapped to ephemeral ports on your computer. For example, a Postgres server may run inside the container using port 5432 but be mapped to a totally different port locally. The service connection will always discover and use the locally mapped port. |
Service connections are established by using the image name of the container. The following service connections are currently supported:
| Connection Details | Matched on |
|---|---|
|
Containers named "symptoma/activemq" |
|
Containers named "cassandra" |
|
Containers named "elasticsearch" |
|
Containers named "gvenzl/oracle-free", "gvenzl/oracle-xe", "mariadb", "mssql/server", "mysql", or "postgres" |
|
Containers named "mongo" |
|
Containers named "neo4j" |
|
Containers named "otel/opentelemetry-collector-contrib" |
|
Containers named "otel/opentelemetry-collector-contrib" |
|
Containers named "apachepulsar/pulsar" |
|
Containers named "gvenzl/oracle-free", "gvenzl/oracle-xe", "mariadb", "mssql/server", "mysql", or "postgres" |
|
Containers named "rabbitmq" |
|
Containers named "redis" |
|
Containers named "openzipkin/zipkin". |
10.3. Custom Images
Sometimes you may need to use your own version of an image to provide a service. You can use any custom image as long as it behaves in the same way as the standard image. Specifically, any environment variables that the standard image supports must also be used in your custom image.
If your image uses a different name, you can use a label in your compose.yml file so that Spring Boot can provide a service connection.
Use a label named org.springframework.boot.service-connection to provide the service name.
For example:
services:
redis:
image: 'mycompany/mycustomredis:7.0'
ports:
- '6379'
labels:
org.springframework.boot.service-connection: redis10.4. Skipping Specific Containers
If you have a container image defined in your compose.yml that you don’t want connected to your application you can use a label to ignore it.
Any container with labeled with org.springframework.boot.ignore will be ignored by Spring Boot.
For example:
services:
redis:
image: 'redis:7.0'
ports:
- '6379'
labels:
org.springframework.boot.ignore: true10.5. Using a Specific Compose File
If your compose file is not in the same directory as your application, or if it’s named differently, you can use spring.docker.compose.file in your application.properties or application.yaml to point to a different file.
Properties can be defined as an exact path or a path that’s relative to your application.
For example:
spring.docker.compose.file=../my-compose.ymlspring:
docker:
compose:
file: "../my-compose.yml"10.6. Waiting for Container Readiness
Containers started by Docker Compose may take some time to become fully ready.
The recommended way of checking for readiness is to add a healthcheck section under the service definition in your compose.yml file.
Since it’s not uncommon for healthcheck configuration to be omitted from compose.yml files, Spring Boot also checks directly for service readiness.
By default, a container is considered ready when a TCP/IP connection can be established to its mapped port.
You can disable this on a per-container basis by adding a org.springframework.boot.readiness-check.tcp.disable label in your compose.yml file.
For example:
services:
redis:
image: 'redis:7.0'
ports:
- '6379'
labels:
org.springframework.boot.readiness-check.tcp.disable: trueYou can also change timeout values in your application.properties or application.yaml file:
spring.docker.compose.readiness.tcp.connect-timeout=10s
spring.docker.compose.readiness.tcp.read-timeout=5sspring:
docker:
compose:
readiness:
tcp:
connect-timeout: 10s
read-timeout: 5sThe overall timeout can be configured using spring.docker.compose.readiness.timeout.
10.7. Controlling the Docker Compose Lifecycle
By default Spring Boot calls docker compose up when your application starts and docker compose stop when it’s shut down.
If you prefer to have different lifecycle management you can use the spring.docker.compose.lifecycle-management property.
The following values are supported:
-
none- Do not start or stop Docker Compose -
start-only- Start Docker Compose when the application starts and leave it running -
start-and-stop- Start Docker Compose when the application starts and stop it when the JVM exits
In addition you can use the spring.docker.compose.start.command property to change whether docker compose up or docker compose start is used.
The spring.docker.compose.stop.command allows you to configure if docker compose down or docker compose stop is used.
The following example shows how lifecycle management can be configured:
spring.docker.compose.lifecycle-management=start-and-stop
spring.docker.compose.start.command=start
spring.docker.compose.stop.command=down
spring.docker.compose.stop.timeout=1mspring:
docker:
compose:
lifecycle-management: start-and-stop
start:
command: start
stop:
command: down
timeout: 1m10.8. Activating Docker Compose Profiles
Docker Compose profiles are similar to Spring profiles in that they let you adjust your Docker Compose configuration for specific environments.
If you want to activate a specific Docker Compose profile you can use the spring.docker.compose.profiles.active property in your application.properties or application.yaml file:
spring.docker.compose.profiles.active=myprofilespring:
docker:
compose:
profiles:
active: "myprofile"10.9. Using Docker Compose in Tests
By default, Spring Boot’s Docker Compose support is disabled when running tests.
To enable Docker Compose support in tests, set spring.docker.compose.skip.in-tests to false.
When using Gradle, you also need to change the configuration of the spring-boot-docker-compose dependency from developmentOnly to testAndDevelopmentOnly:
dependencies {
testAndDevelopmentOnly("org.springframework.boot:spring-boot-docker-compose")
}11. Testcontainers Support
As well as using Testcontainers for integration testing, it’s also possible to use them at development time. The next sections will provide more details about that.
11.1. Using Testcontainers at Development Time
This approach allows developers to quickly start containers for the services that the application depends on, removing the need to manually provision things like database servers. Using Testcontainers in this way provides functionality similar to Docker Compose, except that your container configuration is in Java rather than YAML.
To use Testcontainers at development time you need to launch your application using your “test” classpath rather than “main”. This will allow you to access all declared test dependencies and give you a natural place to write your test configuration.
To create a test launchable version of your application you should create an “Application” class in the src/test directory.
For example, if your main application is in src/main/java/com/example/MyApplication.java, you should create src/test/java/com/example/TestMyApplication.java
The TestMyApplication class can use the SpringApplication.from(…) method to launch the real application:
public class TestMyApplication {
public static void main(String[] args) {
SpringApplication.from(MyApplication::main).run(args);
}
}
fun main(args: Array<String>) {
fromApplication<MyApplication>().run(*args)
}
You’ll also need to define the Container instances that you want to start along with your application.
To do this, you need to make sure that the spring-boot-testcontainers module has been added as a test dependency.
Once that has been done, you can create a @TestConfiguration class that declares @Bean methods for the containers you want to start.
You can also annotate your @Bean methods with @ServiceConnection in order to create ConnectionDetails beans.
See the service connections section for details of the supported technologies.
A typical Testcontainers configuration would look like this:
@TestConfiguration(proxyBeanMethods = false)
public class MyContainersConfiguration {
@Bean
@ServiceConnection
public Neo4jContainer<?> neo4jContainer() {
return new Neo4jContainer<>("neo4j:5");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyContainersConfiguration {
@Bean
@ServiceConnection
fun neo4jContainer(): Neo4jContainer<*> {
return Neo4jContainer("neo4j:5")
}
}
The lifecycle of Container beans is automatically managed by Spring Boot.
Containers will be started and stopped automatically.
|
You can use the spring.testcontainers.beans.startup property to change how containers are started.
By default sequential startup is used, but you may also choose parallel if you wish to start multiple containers in parallel.
|
Once you have defined your test configuration, you can use the with(…) method to attach it to your test launcher:
public class TestMyApplication {
public static void main(String[] args) {
SpringApplication.from(MyApplication::main).with(MyContainersConfiguration.class).run(args);
}
}
fun main(args: Array<String>) {
fromApplication<MyApplication>().with(MyContainersConfiguration::class).run(*args)
}
You can now launch TestMyApplication as you would any regular Java main method application to start your application and the containers that it needs to run.
You can use the Maven goal spring-boot:test-run or the Gradle task bootTestRun to do this from the command line.
|
11.1.1. Contributing Dynamic Properties at Development Time
If you want to contribute dynamic properties at development time from your Container @Bean methods, you can do so by injecting a DynamicPropertyRegistry.
This works in a similar way to the @DynamicPropertySource annotation that you can use in your tests.
It allows you to add properties that will become available once your container has started.
A typical configuration would look like this:
@TestConfiguration(proxyBeanMethods = false)
public class MyContainersConfiguration {
@Bean
public MongoDBContainer mongoDbContainer(DynamicPropertyRegistry properties) {
MongoDBContainer container = new MongoDBContainer("mongo:5.0");
properties.add("spring.data.mongodb.host", container::getHost);
properties.add("spring.data.mongodb.port", container::getFirstMappedPort);
return container;
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyContainersConfiguration {
@Bean
fun monogDbContainer(properties: DynamicPropertyRegistry): MongoDBContainer {
var container = MongoDBContainer("mongo:5.0")
properties.add("spring.data.mongodb.host", container::getHost)
properties.add("spring.data.mongodb.port", container::getFirstMappedPort)
return container
}
}
Using a @ServiceConnection is recommended whenever possible, however, dynamic properties can be a useful fallback for technologies that don’t yet have @ServiceConnection support.
|
11.1.2. Importing Testcontainer Declaration Classes
A common pattern when using Testcontainers is to declare Container instances as static fields.
Often these fields are defined directly on the test class.
They can also be declared on a parent class or on an interface that the test implements.
For example, the following MyContainers interface declares mongo and neo4j containers:
public interface MyContainers {
@Container
@ServiceConnection
MongoDBContainer mongoContainer = new MongoDBContainer("mongo:5.0");
@Container
@ServiceConnection
Neo4jContainer<?> neo4jContainer = new Neo4jContainer<>("neo4j:5");
}
If you already have containers defined in this way, or you just prefer this style, you can import these declaration classes rather than defining your containers as @Bean methods.
To do so, add the @ImportTestcontainers annotation to your test configuration class:
@TestConfiguration(proxyBeanMethods = false)
@ImportTestcontainers(MyContainers.class)
public class MyContainersConfiguration {
}
@TestConfiguration(proxyBeanMethods = false)
@ImportTestcontainers(MyContainers::class)
class MyContainersConfiguration
If you don’t intend to use the service connections feature but want to use @DynamicPropertySource instead, remove the @ServiceConnection annotation from the Container fields.
You can also add @DynamicPropertySource annotated methods to your declaration class.
|
11.1.3. Using DevTools with Testcontainers at Development Time
When using devtools, you can annotate beans and bean methods with @RestartScope.
Such beans won’t be recreated when the devtools restart the application.
This is especially useful for Testcontainer Container beans, as they keep their state despite the application restart.
@TestConfiguration(proxyBeanMethods = false)
public class MyContainersConfiguration {
@Bean
@RestartScope
@ServiceConnection
public MongoDBContainer mongoDbContainer() {
return new MongoDBContainer("mongo:5.0");
}
}
@TestConfiguration(proxyBeanMethods = false)
class MyContainersConfiguration {
@Bean
@RestartScope
@ServiceConnection
fun monogDbContainer(): MongoDBContainer {
return MongoDBContainer("mongo:5.0")
}
}
If you’re using Gradle and want to use this feature, you need to change the configuration of the spring-boot-devtools dependency from developmentOnly to testAndDevelopmentOnly.
With the default scope of developmentOnly, the bootTestRun task will not pick up changes in your code, as the devtools are not active.
|
12. Creating Your Own Auto-configuration
If you work in a company that develops shared libraries, or if you work on an open-source or commercial library, you might want to develop your own auto-configuration. Auto-configuration classes can be bundled in external jars and still be picked up by Spring Boot.
Auto-configuration can be associated to a “starter” that provides the auto-configuration code as well as the typical libraries that you would use with it. We first cover what you need to know to build your own auto-configuration and then we move on to the typical steps required to create a custom starter.
12.1. Understanding Auto-configured Beans
Classes that implement auto-configuration are annotated with @AutoConfiguration.
This annotation itself is meta-annotated with @Configuration, making auto-configurations standard @Configuration classes.
Additional @Conditional annotations are used to constrain when the auto-configuration should apply.
Usually, auto-configuration classes use @ConditionalOnClass and @ConditionalOnMissingBean annotations.
This ensures that auto-configuration applies only when relevant classes are found and when you have not declared your own @Configuration.
You can browse the source code of spring-boot-autoconfigure to see the @AutoConfiguration classes that Spring provides (see the META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports file).
12.2. Locating Auto-configuration Candidates
Spring Boot checks for the presence of a META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports file within your published jar.
The file should list your configuration classes, with one class name per line, as shown in the following example:
com.mycorp.libx.autoconfigure.LibXAutoConfiguration com.mycorp.libx.autoconfigure.LibXWebAutoConfiguration
You can add comments to the imports file using the # character.
|
Auto-configurations must be loaded only by being named in the imports file.
Make sure that they are defined in a specific package space and that they are never the target of component scanning.
Furthermore, auto-configuration classes should not enable component scanning to find additional components.
Specific @Import annotations should be used instead.
|
If your configuration needs to be applied in a specific order, you can use the before, beforeName, after and afterName attributes on the @AutoConfiguration annotation or the dedicated @AutoConfigureBefore and @AutoConfigureAfter annotations.
For example, if you provide web-specific configuration, your class may need to be applied after WebMvcAutoConfiguration.
If you want to order certain auto-configurations that should not have any direct knowledge of each other, you can also use @AutoConfigureOrder.
That annotation has the same semantic as the regular @Order annotation but provides a dedicated order for auto-configuration classes.
As with standard @Configuration classes, the order in which auto-configuration classes are applied only affects the order in which their beans are defined.
The order in which those beans are subsequently created is unaffected and is determined by each bean’s dependencies and any @DependsOn relationships.
12.3. Condition Annotations
You almost always want to include one or more @Conditional annotations on your auto-configuration class.
The @ConditionalOnMissingBean annotation is one common example that is used to allow developers to override auto-configuration if they are not happy with your defaults.
Spring Boot includes a number of @Conditional annotations that you can reuse in your own code by annotating @Configuration classes or individual @Bean methods.
These annotations include:
12.3.1. Class Conditions
The @ConditionalOnClass and @ConditionalOnMissingClass annotations let @Configuration classes be included based on the presence or absence of specific classes.
Due to the fact that annotation metadata is parsed by using ASM, you can use the value attribute to refer to the real class, even though that class might not actually appear on the running application classpath.
You can also use the name attribute if you prefer to specify the class name by using a String value.
This mechanism does not apply the same way to @Bean methods where typically the return type is the target of the condition: before the condition on the method applies, the JVM will have loaded the class and potentially processed method references which will fail if the class is not present.
To handle this scenario, a separate @Configuration class can be used to isolate the condition, as shown in the following example:
@AutoConfiguration
// Some conditions ...
public class MyAutoConfiguration {
// Auto-configured beans ...
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(SomeService.class)
public static class SomeServiceConfiguration {
@Bean
@ConditionalOnMissingBean
public SomeService someService() {
return new SomeService();
}
}
}
@Configuration(proxyBeanMethods = false)
// Some conditions ...
class MyAutoConfiguration {
// Auto-configured beans ...
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(SomeService::class)
class SomeServiceConfiguration {
@Bean
@ConditionalOnMissingBean
fun someService(): SomeService {
return SomeService()
}
}
}
If you use @ConditionalOnClass or @ConditionalOnMissingClass as a part of a meta-annotation to compose your own composed annotations, you must use name as referring to the class in such a case is not handled.
|
12.3.2. Bean Conditions
The @ConditionalOnBean and @ConditionalOnMissingBean annotations let a bean be included based on the presence or absence of specific beans.
You can use the value attribute to specify beans by type or name to specify beans by name.
The search attribute lets you limit the ApplicationContext hierarchy that should be considered when searching for beans.
When placed on a @Bean method, the target type defaults to the return type of the method, as shown in the following example:
@AutoConfiguration
public class MyAutoConfiguration {
@Bean
@ConditionalOnMissingBean
public SomeService someService() {
return new SomeService();
}
}
@Configuration(proxyBeanMethods = false)
class MyAutoConfiguration {
@Bean
@ConditionalOnMissingBean
fun someService(): SomeService {
return SomeService()
}
}
In the preceding example, the someService bean is going to be created if no bean of type SomeService is already contained in the ApplicationContext.
You need to be very careful about the order in which bean definitions are added, as these conditions are evaluated based on what has been processed so far.
For this reason, we recommend using only @ConditionalOnBean and @ConditionalOnMissingBean annotations on auto-configuration classes (since these are guaranteed to load after any user-defined bean definitions have been added).
|
@ConditionalOnBean and @ConditionalOnMissingBean do not prevent @Configuration classes from being created.
The only difference between using these conditions at the class level and marking each contained @Bean method with the annotation is that the former prevents registration of the @Configuration class as a bean if the condition does not match.
|
When declaring a @Bean method, provide as much type information as possible in the method’s return type.
For example, if your bean’s concrete class implements an interface the bean method’s return type should be the concrete class and not the interface.
Providing as much type information as possible in @Bean methods is particularly important when using bean conditions as their evaluation can only rely upon to type information that is available in the method signature.
|
12.3.3. Property Conditions
The @ConditionalOnProperty annotation lets configuration be included based on a Spring Environment property.
Use the prefix and name attributes to specify the property that should be checked.
By default, any property that exists and is not equal to false is matched.
You can also create more advanced checks by using the havingValue and matchIfMissing attributes.
If multiple names are given in the name attribute, all of the properties have to pass the test for the condition to match.
12.3.4. Resource Conditions
The @ConditionalOnResource annotation lets configuration be included only when a specific resource is present.
Resources can be specified by using the usual Spring conventions, as shown in the following example: file:/home/user/test.dat.
12.3.5. Web Application Conditions
The @ConditionalOnWebApplication and @ConditionalOnNotWebApplication annotations let configuration be included depending on whether the application is a web application.
A servlet-based web application is any application that uses a Spring WebApplicationContext, defines a session scope, or has a ConfigurableWebEnvironment.
A reactive web application is any application that uses a ReactiveWebApplicationContext, or has a ConfigurableReactiveWebEnvironment.
The @ConditionalOnWarDeployment and @ConditionalOnNotWarDeployment annotations let configuration be included depending on whether the application is a traditional WAR application that is deployed to a servlet container.
This condition will not match for applications that are run with an embedded web server.
12.3.6. SpEL Expression Conditions
The @ConditionalOnExpression annotation lets configuration be included based on the result of a SpEL expression.
| Referencing a bean in the expression will cause that bean to be initialized very early in context refresh processing. As a result, the bean won’t be eligible for post-processing (such as configuration properties binding) and its state may be incomplete. |
12.4. Testing your Auto-configuration
An auto-configuration can be affected by many factors: user configuration (@Bean definition and Environment customization), condition evaluation (presence of a particular library), and others.
Concretely, each test should create a well defined ApplicationContext that represents a combination of those customizations.
ApplicationContextRunner provides a great way to achieve that.
ApplicationContextRunner doesn’t work when running the tests in a native image.
|
ApplicationContextRunner is usually defined as a field of the test class to gather the base, common configuration.
The following example makes sure that MyServiceAutoConfiguration is always invoked:
private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
.withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration.class));
val contextRunner = ApplicationContextRunner()
.withConfiguration(AutoConfigurations.of(MyServiceAutoConfiguration::class.java))
| If multiple auto-configurations have to be defined, there is no need to order their declarations as they are invoked in the exact same order as when running the application. |
Each test can use the runner to represent a particular use case.
For instance, the sample below invokes a user configuration (UserConfiguration) and checks that the auto-configuration backs off properly.
Invoking run provides a callback context that can be used with AssertJ.
@Test
void defaultServiceBacksOff() {
this.contextRunner.withUserConfiguration(UserConfiguration.class).run((context) -> {
assertThat(context).hasSingleBean(MyService.class);
assertThat(context).getBean("myCustomService").isSameAs(context.getBean(MyService.class));
});
}
@Configuration(proxyBeanMethods = false)
static class UserConfiguration {
@Bean
MyService myCustomService() {
return new MyService("mine");
}
}
@Test
fun defaultServiceBacksOff() {
contextRunner.withUserConfiguration(UserConfiguration::class.java)
.run { context: AssertableApplicationContext ->
assertThat(context).hasSingleBean(MyService::class.java)
assertThat(context).getBean("myCustomService")
.isSameAs(context.getBean(MyService::class.java))
}
}
@Configuration(proxyBeanMethods = false)
internal class UserConfiguration {
@Bean
fun myCustomService(): MyService {
return MyService("mine")
}
}
It is also possible to easily customize the Environment, as shown in the following example:
@Test
void serviceNameCanBeConfigured() {
this.contextRunner.withPropertyValues("user.name=test123").run((context) -> {
assertThat(context).hasSingleBean(MyService.class);
assertThat(context.getBean(MyService.class).getName()).isEqualTo("test123");
});
}
@Test
fun serviceNameCanBeConfigured() {
contextRunner.withPropertyValues("user.name=test123").run { context: AssertableApplicationContext ->
assertThat(context).hasSingleBean(MyService::class.java)
assertThat(context.getBean(MyService::class.java).name).isEqualTo("test123")
}
}
The runner can also be used to display the ConditionEvaluationReport.
The report can be printed at INFO or DEBUG level.
The following example shows how to use the ConditionEvaluationReportLoggingListener to print the report in auto-configuration tests.
class MyConditionEvaluationReportingTests {
@Test
void autoConfigTest() {
new ApplicationContextRunner()
.withInitializer(ConditionEvaluationReportLoggingListener.forLogLevel(LogLevel.INFO))
.run((context) -> {
// Test something...
});
}
}
class MyConditionEvaluationReportingTests {
@Test
fun autoConfigTest() {
ApplicationContextRunner()
.withInitializer(ConditionEvaluationReportLoggingListener.forLogLevel(LogLevel.INFO))
.run { context: AssertableApplicationContext? -> }
}
}
12.4.1. Simulating a Web Context
If you need to test an auto-configuration that only operates in a servlet or reactive web application context, use the WebApplicationContextRunner or ReactiveWebApplicationContextRunner respectively.
12.4.2. Overriding the Classpath
It is also possible to test what happens when a particular class and/or package is not present at runtime.
Spring Boot ships with a FilteredClassLoader that can easily be used by the runner.
In the following example, we assert that if MyService is not present, the auto-configuration is properly disabled:
@Test
void serviceIsIgnoredIfLibraryIsNotPresent() {
this.contextRunner.withClassLoader(new FilteredClassLoader(MyService.class))
.run((context) -> assertThat(context).doesNotHaveBean("myService"));
}
@Test
fun serviceIsIgnoredIfLibraryIsNotPresent() {
contextRunner.withClassLoader(FilteredClassLoader(MyService::class.java))
.run { context: AssertableApplicationContext? ->
assertThat(context).doesNotHaveBean("myService")
}
}
12.5. Creating Your Own Starter
A typical Spring Boot starter contains code to auto-configure and customize the infrastructure of a given technology, let’s call that "acme". To make it easily extensible, a number of configuration keys in a dedicated namespace can be exposed to the environment. Finally, a single "starter" dependency is provided to help users get started as easily as possible.
Concretely, a custom starter can contain the following:
-
The
autoconfiguremodule that contains the auto-configuration code for "acme". -
The
startermodule that provides a dependency to theautoconfiguremodule as well as "acme" and any additional dependencies that are typically useful. In a nutshell, adding the starter should provide everything needed to start using that library.
This separation in two modules is in no way necessary.
If "acme" has several flavors, options or optional features, then it is better to separate the auto-configuration as you can clearly express the fact some features are optional.
Besides, you have the ability to craft a starter that provides an opinion about those optional dependencies.
At the same time, others can rely only on the autoconfigure module and craft their own starter with different opinions.
If the auto-configuration is relatively straightforward and does not have optional features, merging the two modules in the starter is definitely an option.
12.5.1. Naming
You should make sure to provide a proper namespace for your starter.
Do not start your module names with spring-boot, even if you use a different Maven groupId.
We may offer official support for the thing you auto-configure in the future.
As a rule of thumb, you should name a combined module after the starter.
For example, assume that you are creating a starter for "acme" and that you name the auto-configure module acme-spring-boot and the starter acme-spring-boot-starter.
If you only have one module that combines the two, name it acme-spring-boot-starter.
12.5.2. Configuration keys
If your starter provides configuration keys, use a unique namespace for them.
In particular, do not include your keys in the namespaces that Spring Boot uses (such as server, management, spring, and so on).
If you use the same namespace, we may modify these namespaces in the future in ways that break your modules.
As a rule of thumb, prefix all your keys with a namespace that you own (for example acme).
Make sure that configuration keys are documented by adding field javadoc for each property, as shown in the following example:
@ConfigurationProperties("acme")
public class AcmeProperties {
/**
* Whether to check the location of acme resources.
*/
private boolean checkLocation = true;
/**
* Timeout for establishing a connection to the acme server.
*/
private Duration loginTimeout = Duration.ofSeconds(3);
}
@ConfigurationProperties("acme")
class AcmeProperties(
/**
* Whether to check the location of acme resources.
*/
var isCheckLocation: Boolean = true,
/**
* Timeout for establishing a connection to the acme server.
*/
var loginTimeout:Duration = Duration.ofSeconds(3))
You should only use plain text with @ConfigurationProperties field Javadoc, since they are not processed before being added to the JSON.
|
Here are some rules we follow internally to make sure descriptions are consistent:
-
Do not start the description by "The" or "A".
-
For
booleantypes, start the description with "Whether" or "Enable". -
For collection-based types, start the description with "Comma-separated list"
-
Use
java.time.Durationrather thanlongand describe the default unit if it differs from milliseconds, such as "If a duration suffix is not specified, seconds will be used". -
Do not provide the default value in the description unless it has to be determined at runtime.
Make sure to trigger meta-data generation so that IDE assistance is available for your keys as well.
You may want to review the generated metadata (META-INF/spring-configuration-metadata.json) to make sure your keys are properly documented.
Using your own starter in a compatible IDE is also a good idea to validate that quality of the metadata.
12.5.3. The “autoconfigure” Module
The autoconfigure module contains everything that is necessary to get started with the library.
It may also contain configuration key definitions (such as @ConfigurationProperties) and any callback interface that can be used to further customize how the components are initialized.
You should mark the dependencies to the library as optional so that you can include the autoconfigure module in your projects more easily.
If you do it that way, the library is not provided and, by default, Spring Boot backs off.
|
Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file (META-INF/spring-autoconfigure-metadata.properties).
If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time.
When building with Maven, it is recommended to add the following dependency in a module that contains auto-configurations:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure-processor</artifactId>
<optional>true</optional>
</dependency>If you have defined auto-configurations directly in your application, make sure to configure the spring-boot-maven-plugin to prevent the repackage goal from adding the dependency into the uber jar:
<project>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<configuration>
<excludes>
<exclude>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure-processor</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
</project>With Gradle, the dependency should be declared in the annotationProcessor configuration, as shown in the following example:
dependencies {
annotationProcessor "org.springframework.boot:spring-boot-autoconfigure-processor"
}12.5.4. Starter Module
The starter is really an empty jar. Its only purpose is to provide the necessary dependencies to work with the library. You can think of it as an opinionated view of what is required to get started.
Do not make assumptions about the project in which your starter is added. If the library you are auto-configuring typically requires other starters, mention them as well. Providing a proper set of default dependencies may be hard if the number of optional dependencies is high, as you should avoid including dependencies that are unnecessary for a typical usage of the library. In other words, you should not include optional dependencies.
Either way, your starter must reference the core Spring Boot starter (spring-boot-starter) directly or indirectly (there is no need to add it if your starter relies on another starter).
If a project is created with only your custom starter, Spring Boot’s core features will be honoured by the presence of the core starter.
|
13. Kotlin Support
Kotlin is a statically-typed language targeting the JVM (and other platforms) which allows writing concise and elegant code while providing interoperability with existing libraries written in Java.
Spring Boot provides Kotlin support by leveraging the support in other Spring projects such as Spring Framework, Spring Data, and Reactor. See the Spring Framework Kotlin support documentation for more information.
The easiest way to start with Spring Boot and Kotlin is to follow this comprehensive tutorial.
You can create new Kotlin projects by using start.spring.io.
Feel free to join the #spring channel of Kotlin Slack or ask a question with the spring and kotlin tags on Stack Overflow if you need support.
13.1. Requirements
Spring Boot requires at least Kotlin 1.7.x and manages a suitable Kotlin version through dependency management.
To use Kotlin, org.jetbrains.kotlin:kotlin-stdlib and org.jetbrains.kotlin:kotlin-reflect must be present on the classpath.
The kotlin-stdlib variants kotlin-stdlib-jdk7 and kotlin-stdlib-jdk8 can also be used.
Since Kotlin classes are final by default, you are likely to want to configure kotlin-spring plugin in order to automatically open Spring-annotated classes so that they can be proxied.
Jackson’s Kotlin module is required for serializing / deserializing JSON data in Kotlin. It is automatically registered when found on the classpath. A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.
| These dependencies and plugins are provided by default if one bootstraps a Kotlin project on start.spring.io. |
13.2. Null-safety
One of Kotlin’s key features is null-safety.
It deals with null values at compile time rather than deferring the problem to runtime and encountering a NullPointerException.
This helps to eliminate a common source of bugs without paying the cost of wrappers like Optional.
Kotlin also allows using functional constructs with nullable values as described in this comprehensive guide to null-safety in Kotlin.
Although Java does not allow one to express null-safety in its type system, Spring Framework, Spring Data, and Reactor now provide null-safety of their API through tooling-friendly annotations. By default, types from Java APIs used in Kotlin are recognized as platform types for which null-checks are relaxed. Kotlin’s support for JSR 305 annotations combined with nullability annotations provide null-safety for the related Spring API in Kotlin.
The JSR 305 checks can be configured by adding the -Xjsr305 compiler flag with the following options: -Xjsr305={strict|warn|ignore}.
The default behavior is the same as -Xjsr305=warn.
The strict value is required to have null-safety taken in account in Kotlin types inferred from Spring API but should be used with the knowledge that Spring API nullability declaration could evolve even between minor releases and more checks may be added in the future).
| Generic type arguments, varargs and array elements nullability are not yet supported. See SPR-15942 for up-to-date information. Also be aware that Spring Boot’s own API is not yet annotated. |
13.3. Kotlin API
13.3.1. runApplication
Spring Boot provides an idiomatic way to run an application with runApplication<MyApplication>(*args) as shown in the following example:
@SpringBootApplication
class MyApplication
fun main(args: Array<String>) {
runApplication<MyApplication>(*args)
}
This is a drop-in replacement for SpringApplication.run(MyApplication::class.java, *args).
It also allows customization of the application as shown in the following example:
runApplication<MyApplication>(*args) {
setBannerMode(OFF)
}
13.3.2. Extensions
Kotlin extensions provide the ability to extend existing classes with additional functionality. The Spring Boot Kotlin API makes use of these extensions to add new Kotlin specific conveniences to existing APIs.
TestRestTemplate extensions, similar to those provided by Spring Framework for RestOperations in Spring Framework, are provided.
Among other things, the extensions make it possible to take advantage of Kotlin reified type parameters.
13.4. Dependency management
In order to avoid mixing different versions of Kotlin dependencies on the classpath, Spring Boot imports the Kotlin BOM.
With Maven, the Kotlin version can be customized by setting the kotlin.version property and plugin management is provided for kotlin-maven-plugin.
With Gradle, the Spring Boot plugin automatically aligns the kotlin.version with the version of the Kotlin plugin.
Spring Boot also manages the version of Coroutines dependencies by importing the Kotlin Coroutines BOM.
The version can be customized by setting the kotlin-coroutines.version property.
org.jetbrains.kotlinx:kotlinx-coroutines-reactor dependency is provided by default if one bootstraps a Kotlin project with at least one reactive dependency on start.spring.io.
|
13.5. @ConfigurationProperties
@ConfigurationProperties when used in combination with constructor binding supports data classes with immutable val properties as shown in the following example:
@ConfigurationProperties("example.kotlin")
data class KotlinExampleProperties(
val name: String,
val description: String,
val myService: MyService) {
data class MyService(
val apiToken: String,
val uri: URI
)
}
Due to the limitations of their interoperability with Java, support for value classes is limited. In particular, relying upon a value class’s default value will not work with configuration property binding. In such cases, a data class should be used instead.
To generate your own metadata using the annotation processor, kapt should be configured with the spring-boot-configuration-processor dependency.
Note that some features (such as detecting the default value or deprecated items) are not working due to limitations in the model kapt provides.
|
13.6. Testing
While it is possible to use JUnit 4 to test Kotlin code, JUnit 5 is provided by default and is recommended.
JUnit 5 enables a test class to be instantiated once and reused for all of the class’s tests.
This makes it possible to use @BeforeAll and @AfterAll annotations on non-static methods, which is a good fit for Kotlin.
To mock Kotlin classes, MockK is recommended.
If you need the MockK equivalent of the Mockito specific @MockBean and @SpyBean annotations, you can use SpringMockK which provides similar @MockkBean and @SpykBean annotations.
13.7. Resources
13.7.1. Further reading
-
Kotlin Slack (with a dedicated #spring channel)
-
Tutorial: building web applications with Spring Boot and Kotlin
-
A Geospatial Messenger with Kotlin, Spring Boot and PostgreSQL
13.7.2. Examples
-
spring-boot-kotlin-demo: regular Spring Boot + Spring Data JPA project
-
mixit: Spring Boot 2 + WebFlux + Reactive Spring Data MongoDB
-
spring-kotlin-fullstack: WebFlux Kotlin fullstack example with Kotlin2js for frontend instead of JavaScript or TypeScript
-
spring-petclinic-kotlin: Kotlin version of the Spring PetClinic Sample Application
-
spring-kotlin-deepdive: a step by step migration for Boot 1.0 + Java to Boot 2.0 + Kotlin
-
spring-boot-coroutines-demo: Coroutines sample project
14. SSL
Spring Boot provides the ability to configure SSL trust material that can be applied to several types of connections in order to support secure communications.
Configuration properties with the prefix spring.ssl.bundle can be used to specify named sets of trust material and associated information.
14.1. Configuring SSL With Java KeyStore Files
Configuration properties with the prefix spring.ssl.bundle.jks can be used to configure bundles of trust material created with the Java keytool utility and stored in Java KeyStore files in the JKS or PKCS12 format.
Each bundle has a user-provided name that can be used to reference the bundle.
When used to secure an embedded web server, a keystore is typically configured with a Java KeyStore containing a certificate and private key as shown in this example:
spring.ssl.bundle.jks.mybundle.key.alias=application
spring.ssl.bundle.jks.mybundle.keystore.location=classpath:application.p12
spring.ssl.bundle.jks.mybundle.keystore.password=secret
spring.ssl.bundle.jks.mybundle.keystore.type=PKCS12spring:
ssl:
bundle:
jks:
mybundle:
key:
alias: "application"
keystore:
location: "classpath:application.p12"
password: "secret"
type: "PKCS12"When used to secure a client-side connection, a truststore is typically configured with a Java KeyStore containing the server certificate as shown in this example:
spring.ssl.bundle.jks.mybundle.truststore.location=classpath:server.p12
spring.ssl.bundle.jks.mybundle.truststore.password=secretspring:
ssl:
bundle:
jks:
mybundle:
truststore:
location: "classpath:server.p12"
password: "secret"See JksSslBundleProperties for the full set of supported properties.
| If you’re using environment variables to configure the bundle, the name of the bundle is always converted to lowercase. |
14.2. Configuring SSL With PEM-encoded Certificates
Configuration properties with the prefix spring.ssl.bundle.pem can be used to configure bundles of trust material in the form of PEM-encoded text.
Each bundle has a user-provided name that can be used to reference the bundle.
When used to secure an embedded web server, a keystore is typically configured with a certificate and private key as shown in this example:
spring.ssl.bundle.pem.mybundle.keystore.certificate=classpath:application.crt
spring.ssl.bundle.pem.mybundle.keystore.private-key=classpath:application.keyspring:
ssl:
bundle:
pem:
mybundle:
keystore:
certificate: "classpath:application.crt"
private-key: "classpath:application.key"When used to secure a client-side connection, a truststore is typically configured with the server certificate as shown in this example:
spring.ssl.bundle.pem.mybundle.truststore.certificate=classpath:server.crtspring:
ssl:
bundle:
pem:
mybundle:
truststore:
certificate: "classpath:server.crt"|
PEM content can be used directly for both the The following example shows how a truststore certificate can be defined: Properties
Yaml
|
See PemSslBundleProperties for the full set of supported properties.
| If you’re using environment variables to configure the bundle, the name of the bundle is always converted to lowercase. |
14.3. Applying SSL Bundles
Once configured using properties, SSL bundles can be referred to by name in configuration properties for various types of connections that are auto-configured by Spring Boot. See the sections on embedded web servers, data technologies, and REST clients for further information.
14.4. Using SSL Bundles
Spring Boot auto-configures a bean of type SslBundles that provides access to each of the named bundles configured using the spring.ssl.bundle properties.
An SslBundle can be retrieved from the auto-configured SslBundles bean and used to create objects that are used to configure SSL connectivity in client libraries.
The SslBundle provides a layered approach of obtaining these SSL objects:
-
getStores()provides access to the key store and trust storejava.security.KeyStoreinstances as well as any required key store password. -
getManagers()provides access to thejava.net.ssl.KeyManagerFactoryandjava.net.ssl.TrustManagerFactoryinstances as well as thejava.net.ssl.KeyManagerandjava.net.ssl.TrustManagerarrays that they create. -
createSslContext()provides a convenient way to obtain a newjava.net.ssl.SSLContextinstance.
In addition, the SslBundle provides details about the key being used, the protocol to use and any option that should be applied to the SSL engine.
The following example shows retrieving an SslBundle and using it to create an SSLContext:
@Component
public class MyComponent {
public MyComponent(SslBundles sslBundles) {
SslBundle sslBundle = sslBundles.getBundle("mybundle");
SSLContext sslContext = sslBundle.createSslContext();
// do something with the created sslContext
}
}
@Component
class MyComponent(sslBundles: SslBundles) {
init {
val sslBundle = sslBundles.getBundle("mybundle")
val sslContext = sslBundle.createSslContext()
// do something with the created sslContext
}
}
14.5. Reloading SSL bundles
SSL bundles can be reloaded when the key material changes. The component consuming the bundle has to be compatible with reloadable SSL bundles. Currently the following components are compatible:
-
Tomcat web server
-
Netty web server
To enable reloading, you need to opt-in via a configuration property as shown in this example:
spring.ssl.bundle.pem.mybundle.reload-on-update=true
spring.ssl.bundle.pem.mybundle.keystore.certificate=file:/some/directory/application.crt
spring.ssl.bundle.pem.mybundle.keystore.private-key=file:/some/directory/application.keyspring:
ssl:
bundle:
pem:
mybundle:
reload-on-update: true
keystore:
certificate: "file:/some/directory/application.crt"
private-key: "file:/some/directory/application.key"A file watcher is then watching the files and if they change, the SSL bundle will be reloaded. This in turn triggers a reload in the consuming component, e.g. Tomcat rotates the certificates in the SSL enabled connectors.
You can configure the quiet period (to make sure that there are no more changes) of the file watcher with the spring.ssl.bundle.watch.file.quiet-period property.
15. What to Read Next
If you want to learn more about any of the classes discussed in this section, see the Spring Boot API documentation or you can browse the source code directly. If you have specific questions, see the how-to section.
If you are comfortable with Spring Boot’s core features, you can continue on and read about production-ready features.