@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.
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.
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.
EventListenerMethodProcessor
Modifier and Type | Optional Element and Description |
---|---|
Class<?>[] |
classes
The event classes that this listener handles.
|
String |
condition
Spring Expression Language (SpEL) attribute 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
Default is ""
, meaning the event is always handled.
The SpEL expression evaluates against a dedicated context that provides the following meta-data:
#root.event
, #root.args
for
references to the ApplicationEvent
and method arguments
respectively.#root.args[0]
, #p0
or #a0
. Arguments can also be accessed by name if that
information is available.