Asynchronous Tasks

From Documentation

Asynchronous Tasks

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 EventListener or SerializableEventListener).
  3. Execute the listener asynchronously by Executions.schedule(Desktop, EventListener, Event).

Here is the code snippet:

 1     @Listen("onClick = #start")
 2     public void start() throws ExecutionException, InterruptedException {
 3         // run in a separate thread
 4         CompletableFuture.runAsync(() -> {
 5             Threads.sleep(3000); //simulate a long task
 6             Executions.schedule(desktop,
 7                 new EventListener<Event>() {
 8                     public void onEvent(Event event) {
 9                         //update UI
10                         status.setValue("done at " +;
11                     }
12                 }, new Event("myEvent"));
13         });
14     }

Notice that Executions.schedule(Desktop, EventListener, 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

Last Update : 2022/06/15

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.

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