Subscribe by @Subscribe

A method (as if in an EventListener) in SelectorComposer can subscribe to an EventQueue by @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 org.zkoss.zk.ui.event.EventQueue.

EventQueue Scope

You can subscribe to EventQueue of different scopes.

@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 org.zkoss.zk.ui.event.EventQueues.

Event Name

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
    // ...
}

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