注释类型 EventListener
@Target({METHOD,ANNOTATION_TYPE}) @Retention(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 theclasses()
javadoc for further details.Events can be
ApplicationEvent
instances as well as arbitrary objects.Processing of
@EventListener
annotations is performed via the internalEventListenerMethodProcessor
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.- 从以下版本开始:
- 4.2
- 作者:
- Stephane Nicoll, Sam Brannen
- 另请参阅:
EventListenerMethodProcessor
- If an asynchronous event listener throws an exception, it is not propagated to the caller. See
classes
@AliasFor("value") 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.
- 默认值:
- {}
condition
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
orevent
for references to theApplicationEvent
#root.args
orargs
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.
- 默认值:
- ""