@Target(value={METHOD,ANNOTATION_TYPE}) @Retention(value=RUNTIME) @Documented public @interface EventListener
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.
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.
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.
AsyncUncaughtExceptionHandler
for more details.ApplicationEventPublisher
to publish the event manually.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.
EventListenerMethodProcessor
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.
|
Class<?>[] |
value
Alias for
classes() . |
@AliasFor(value="value") public abstract Class<?>[] classes
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.
public abstract String condition
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#root.args[0]
, args[0]
,
#a0
, or #p0
.