Manage GUI and EDT in a multi-task application

Question

I developed a Java application for creating and extracting an archive - like WinRAR. You can create several archives at the same time with multithreading. And recently, I wanted to add an information status during the archive creation in the form of JProgressBar in a new JFrame at every creation.

But my problem is generating information in the new status frame and the thread which create the archive. That's why I create the JFrame in the archive thread for updating the progress bar currently.

But like I could read it in a diverse information source and on your answers/comments, it's against Java Swing and performance; I can't create swing object elsewhere that the EDT.

But then, how should I solve my problem? How can I etablish communication between the writing of my archive and its status JFrame (with JProgressBar)?

---

EDIT:

I implemented SwingWorker to manage the GUI in my application. Now it's done, I have an other question:

With SwingWorker, how do I act on the background task with an event on status Frame's button? (Example: pause compression or stop it.)

Answer 1

1. Put and display JProgressBar in a JDialog, and don't create a new Top-Level Container. Create that once and re-use that

2. Long timed and heavy code would be better redirected to the BackGround Task

3. You can move with progress in JProgressBar from a background task

   • only if GUI related code is done on EDT more Concurrency in Swing

   • and there are two correct ways to do it

     • by using SwingWorker

     • from Runnable#Thread but GUI rellated code must be wrapped into invokeLater()

Answer 2

As suggested by others, the best way is to use SwingWorker.

SwingWorker properties are listenable and listeners are always called in the EDT, thus, you could do something like:

public class ArchivingWorker extends SwingWorker<Void, Void> {
    JProgressBar progressBar = null;
    // Other members here...
    ...

    public ArchivingWorker(...) {
        // Any specific initialization here (in EDT)
        addPropertyChangeListener(new PropertyChangeListener() {
            @Override void propertyChange(PropertyChangeEvent e) {
                if (    "state".equals(e.getPropertyName())
                    &&  e.getNewValue() == StateValue.STARTED) {
                    // Background thread has just started, show a progress dialog here
                    progressBar = new JProgressBar();
                    ...
                }
                else if ("progress".equals(e.getPropertyName())) {
                    // Update progress bar here with e.getNewValue()
                    ...
                }
            }
        });
    }

    @Override protected Void doInBackground() {
        // Archiving process here and update progress from time to time
        setProgress(progress);

        return null;
    }

    @Override protected void done() {
        // Ensure that archiving process worked correctly (no exception)
        try {
            get();
        } catch (Exception e) {
            // Handle exception (user feedback or whatever)
        } finally {
            // Close progress dialog
            ...
        }
    }
}

Then you can use ArchivingWorker as you need it:

ArchivngWorker worker = new ArchivingWorker(...);
worker.execute();

Answer 3

The answer provided by @mKorbel is fine, but there really is no need to use another top-level container (e.g. a JDialog) to display the progress bar. Instead, you can use the Glass Pane of the JFrame instance.