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public interface EventBus
Dispatches events to listeners, and provides ways for listeners to register themselves.
The EventBus allows publish-subscribe-style communication between components without requiring the components to explicitly register with one another (and thus be aware of each other). It is designed exclusively to replace traditional Java in-process event distribution using explicit registration. It is not a general-purpose publish-subscribe system, nor is it intended for interprocess communication.
Subscribe
annotation;register(Object)
method.
post(Object)
method. The EventBus instance will determine the type
of event and route it to all registered listeners.
Events are routed based on their type — an event will be delivered to any handler for any type to which the event is assignable. This includes implemented interfaces, all superclasses, and all interfaces implemented by superclasses.
When post
is called, all registered handlers for an event are run
in sequence, so handlers should be reasonably quick. If an event may trigger
an extended process (such as a database load), spawn a thread or queue it for
later. (For a convenient way to do this, use an AsyncEventBus
.)
Handlers should not, in general, throw. If they do, the EventBus will catch and log the exception. This is rarely the right solution for error handling and should not be relied upon; it is intended solely to help find problems during development.
The EventBus guarantees that it will not call a handler method from
multiple threads simultaneously, unless the method explicitly allows it by
bearing the AllowConcurrentEvents
annotation. If this annotation is
not present, handler methods need not worry about being reentrant, unless
also called from outside the EventBus.
DeadEvent
and reposted.
If a handler for a supertype of all events (such as Object) is registered,
no event will ever be considered dead, and no DeadEvents will be generated.
Accordingly, while DeadEvent extends Object
, a handler registered to
receive any Object will never receive a DeadEvent.
This class is safe for concurrent use.
Nested Class Summary | |
---|---|
static interface |
EventBus.LoadOnStart
Marker interface for all handlers that should be automatically registered with event bus when event bus is created. |
Method Summary | |
---|---|
EventBus |
post(Object event)
Posts an event. |
EventBus |
register(Object handler)
Registers an event handler with this event bus. |
EventBus |
unregister(Object handler)
Unregisters an event handler from this event bus. |
Method Detail |
---|
EventBus register(Object handler)
handler
- to be registered
EventBus unregister(Object handler)
handler
- to be registered
EventBus post(Object event)
event
- an event
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