org.springframework.context.event

Annotation Type EventListener

@Target(value={METHOD,ANNOTATION_TYPE})
 @Retention(value=RUNTIME)
 @Documented
public @interface EventListener

Annotation that marks a method as a listener for application events.

If an annotated method supports a single event type, the method may declare a single parameter that reflects the event type to listen to. If an annotated method supports multiple event types, this annotation may refer to one or more supported event types using the classes attribute. See the classes() javadoc for further details.

Events can be ApplicationEvent instances as well as arbitrary objects.

Processing of @EventListener annotations is performed via the internal EventListenerMethodProcessor bean which gets registered automatically when using Java config or manually via the <context:annotation-config/> or <context:component-scan/> element when using XML config.

Annotated methods may have a non-void return type. When they do, the result of the method invocation is sent as a new event. If the return type is either an array or a collection, each element is sent as a new individual event.

This annotation may be used as a meta-annotation to create custom composed annotations.

Exception Handling

While it is possible for an event listener to declare that it throws arbitrary exception types, any checked exceptions thrown from an event listener will be wrapped in an UndeclaredThrowableException since the event publisher can only handle runtime exceptions.

Asynchronous Listeners

If you want a particular listener to process events asynchronously, you can use Spring's @Async support, but be aware of the following limitations when using asynchronous events.

• If an asynchronous event listener throws an exception, it is not propagated to the caller. See AsyncUncaughtExceptionHandler for more details.
• Asynchronous event listener methods cannot publish a subsequent event by returning a value. If you need to publish another event as the result of the processing, inject an ApplicationEventPublisher to publish the event manually.

Ordering Listeners

It is also possible to define the order in which listeners for a certain event are to be invoked. To do so, add Spring's common @Order annotation alongside this event listener annotation.

Since:

4.2

Author:

Stephane Nicoll, Sam Brannen

See Also:

EventListenerMethodProcessor, TransactionalEventListener

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
Class<?>[]	classes The event classes that this listener handles.
String	condition Spring Expression Language (SpEL) expression used for making the event handling conditional.
String	id An optional identifier for the listener, defaulting to the fully-qualified signature of the declaring method (e.g.
Class<?>[]	value Alias for classes().

Element Detail

value

@AliasFor(value="classes")
public abstract Class<?>[] value

Alias for classes().

Default:

{}

classes

@AliasFor(value="value")
public abstract Class<?>[] classes

The event classes that this listener handles.

If this attribute is specified with a single value, the annotated method may optionally accept a single parameter. However, if this attribute is specified with multiple values, the annotated method must not declare any parameters.

Default:

{}

condition

public abstract String condition

Spring Expression Language (SpEL) expression used for making the event handling conditional.

The event will be handled if the expression evaluates to boolean true or one of the following strings: "true", "on", "yes", or "1".

The default expression is "", meaning the event is always handled.

The SpEL expression will be evaluated against a dedicated context that provides the following metadata:

• #root.event or event for references to the ApplicationEvent
• #root.args or args for references to the method arguments array
• Method arguments can be accessed by index. For example, the first argument can be accessed via #root.args[0], args[0], #a0, or #p0.
• Method arguments can be accessed by name (with a preceding hash tag) if parameter names are available in the compiled byte code.

Default:

""

id

public abstract String id

An optional identifier for the listener, defaulting to the fully-qualified signature of the declaring method (e.g. "mypackage.MyClass.myMethod()").

Since:

5.3.5

See Also:

SmartApplicationListener.getListenerId(), ApplicationEventMulticaster.removeApplicationListeners(Predicate)

Default:

""