Subscribe to EventQueues

A Simple Example

• Available for ZK:
• 

An method (as if in an EventListener) in SelectorComposer can subscribe to an EventQueue by annotate it with Subscribe. For example,

// in sender composer
public void publish() {
	EventQueue<Event> eq = EventQueues.lookup("queue1", EventQueues.DESKTOP, true);
	eq.publish(new Event("onMyEvent", component, data));
}

// in receiver composer
@Subscribe("queue1")
public void receive(Event event) {
	// this method will be called when EventQueue "queue1" of Desktop scope is published
	Object data = event.getData();
	Component target = event.getTarget();
}

• Notice the queue name should match.
• ZK executes both methods in a servlet thread, so if they execute a time-consuming operation, they will block users.

In the example above, when you publish an event in the EventQueue, the subscribed method will be called. This is a useful mechanism to communicate among composers. See also EventQueue.

EventQueue Scope

You can subscribe to EventQueue of different scope.

@Subscribe(value = "queue2", scope = EventQueues.SESSION)
public void method2(Event event) {
	// this method will be called when EventQueue "queue2" of Session scope is published
}
public void publish() {
	EventQueue<Event> eq = EventQueues.lookup("queue2", EventQueues.SESSION, true);
	eq.publish(new Event("onMyEvent", component, data));
}

Available scopes are: Desktop, Group, Session, Application. Note that Group scope requires ZK EE. See also EventQueues.

Event Name

Since 7.0.3, you can also listen to a specified event name

@Subscribe(value = "queue2", eventName = "event1")
public void method2(Event event) {
	// this method will be called when EventQueue "queue2" of Session scope is published
}
public void publish() {
	EventQueue<Event> eq = EventQueues.lookup("queue2", EventQueues.DESKTOP, true);
	eq.publish(new Event("event1", component, data));
}

Subscriber Method Parameter

The method which subscribes to the EventQueue takes either no parameter, or one parameter of a type Event.

@Subscribe("queue3")
public void method3() { // the event parameter can be omitted
	// ...
}

Since 7.0.3, ZK automatically maps event data into the method parameters in order.

@Subscribe("queue3")
public void method3(int i, String s) { 
	// i will be 100, s will be "eventData"
	// ...
}

public void publish() {
	EventQueue<Event> eq = EventQueues.lookup("queue3", EventQueues.DESKTOP, true);
	eq.publish(new Event("event1", component, new Object[]{100, "eventData"}));
}

If you put the event at the first one, it also works well.

@Subscribe("queue3")
public void method3(Event event, int i, String s) { 
	// ...
}

To recap, we now have four ways to use a parameter:

• method()
• method(Event event)
• method(Event event, int d1, String d2, ....)
• method(int d1, String d2, ...)

Auto-Unsubscribed

@Subscribe will unsubscribe the subscribed event-queue automatically when the applied component (or its ancestor) of a composer is detached.

Version History

Version	Date	Content
6.0.1	April 2012	@Subscribe was introduced.
7.0.3	June 2014	ZK-2076 Enhance Subscribe annotation to map java method by the event name and the parameter type in order