If you run an application logic in a task thread (not in a servlet thread), and you don’t want to update UI in the same thread. All you need to do is:

  1. enable server push
  2. Implement the UI updates in an event listener (implement org.zkoss.zk.ui.event.EventListener or org.zkoss.zk.ui.event.SerializableEventListener).
  3. Execute the listener asynchronously by org.zkoss.zk.ui.Executions#schedule(org.zkoss.zk.ui.Desktop, org.zkoss.zk.ui.event.EventListener, org.zkoss.zk.ui.event.Event).

Here is the code snippet:

    @Listen("onClick = #start")
    public void start() throws ExecutionException, InterruptedException {
        // run in a separate thread
        CompletableFuture.runAsync(() -> {
            Threads.sleep(3000); //simulate a long task
            Executions.schedule(desktop,
                new EventListener<Event>() {
                    public void onEvent(Event event) {
                        //update UI
                        status.setValue("done at " + LocalDateTime.now());
                    }
                }, new Event("myEvent"));
        });
    }

Notice that org.zkoss.zk.ui.Executions#schedule(org.zkoss.zk.ui.Desktop, org.zkoss.zk.ui.event.EventListener, org.zkoss.zk.ui.event.Event) can be called anywhere, including another event listener or a task thread. In other words, you don’t have to fork a new thread to use this feature.

Notice that, since there is at most one thread to access the UI of a given desktop, the event listener must NOT be time-consuming. Otherwise, it will block other event listeners from execution. Thus, if you have a long operation to do, you could use event queue’s asynchronous event listener, or implement it as a synchronous task and handle lengthy operation outside of the activation block.

Version History

Version Date Content
5.0.6 November 2010 This feature was introduced. With 5.0.5 or prior, you have to use Event Queues or Synchronous Tasks.