f0fca890bb
Add support for annotation-based event listeners. Enabled automatically
when using Java configuration or can be enabled explicitly via the
regular <context:annotation-driven/> XML element. Detect methods of
managed beans annotated with @EventListener, either directly or through
a meta-annotation.
Annotated methods must define the event type they listen to as a single
parameter argument. Events are automatically filtered out according to
the method signature. When additional runtime filtering is required, one
can specify the `condition` attribute of the annotation that defines a
SpEL expression that should match to actually invoke the method for a
particular event. The root context exposes the actual `event`
(`#root.event`) and method arguments (`#root.args`). Individual method
arguments are also exposed via either the `a` or `p` alias (`#a0` refers
to the first method argument). Finally, methods arguments are exposed via
their names if that information can be discovered.
Events can be either an ApplicationEvent or any arbitrary payload. Such
payload is wrapped automatically in a PayloadApplicationEvent and managed
explicitly internally. As a result, users can now publish and listen
for arbitrary objects.
If an annotated method has a return value, an non null result is actually
published as a new event, something like:
@EventListener
public FooEvent handle(BarEvent event) { ... }
Events can be handled in an aynchronous manner by adding `@Async` to the
event method declaration and enabling such infrastructure. Events can
also be ordered by adding an `@Order` annotation to the event method.
Issue: SPR-11622
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