Event Queues

An event queue is an event-based publish-subscribe solution for the application information delivery and messaging. It provides asynchronous communication for different modules/roles in a loosely-coupled and autonomous fashion.

By publishing, a module (publisher) sends out messages without explicitly specifying or having knowledge of intended recipients. By subscribing, a receiving module (subscriber) receives messages that the subscriber has registered an interest in, without explicitly specifying or knowing the publisher.

ZK generalizes the event queue to support the server push. The use is straightforward: specifying the scope of a given event queue as EventQueues.APPLICATION (or EventQueues.SESSION, but rare). For example,

EventQueue que = EventQueues.lookup("chat", EventQueues.APPLICATION, true);

For more information about event queues, please refer to the Event Handling: Event Queues section.

For the information about low-level API, please refer to Asynchronous Tasks section, if the task can execute asynchronously; or Synchronous Tasks if it must execute synchronously.

Version History

Version	Date	Content
5.0.6	November 2010	The event queue won't start any working threads and they are serializable, so it is safe to use them in a clustering environment.