Java Swing Threading with Updatable JProgressBar

Question

First off I've been working with Java's Concurrency package quite a bit lately but I have found an issue that I am stuck on. I want to have and Application and the Application can have a SplashScreen with a status bar and the loading of other data. So I decided to use SwingUtilities.invokeAndWait( call the splash component here ). The SplashScreen then appears with a JProgressBar and runs a group of threads. But I can't seem to get a good handle on things. I've looked over SwingWorker and tried using it for this purpose but the thread just returns. Here is a bit of pseudo code. and the points I'm trying to achieve.

• Have an Application that has a SplashScreen that pauses while loading info
• Be able to run multiple threads under the SplashScreen
• Have the progress bar of the SplashScreen Update-able yet not exit until all threads are done.

Launching splash screen

try {
    SwingUtilities.invokeAndWait( SplashScreen );
} catch (InterruptedException e) {
} catch (InvocationTargetException e) { }

Splash screen construction

SplashScreen extends JFrame implements Runnable{

    public void run() {
        //run threads
        //while updating status bar
    }
}

I have tried many things including SwingWorkers, Threads using CountDownLatch's, and others. The CountDownLatch's actually worked in the manner I wanted to do the processing but I was unable to update the GUI. When using the SwingWorkers either the invokeAndWait was basically nullified (which is their purpose) or it wouldn't update the GUI still even when using a PropertyChangedListener. If someone else has a couple ideas it would be great to hear them. Thanks in advance.

I actually got ready to post better code to help out and found my solution. I thank you for all who helped.

Answer 1

No need to call the frame inside invokeAndWait but you should update progress bar state like this.

try {
   SwingUtilities.invokeAndWait( new Runnable() {
     public void run() {
//update state of the progress bar here
     }
   });
 } catch (InterruptedException e) {
 } catch (InvocationTargetException e) { }

Answer 2

For running a series of operations in the background and reporting progress, use SwingWorker.

The background method does the background processing.
Use the publish method to post periodic status updates.
Override the process method to handle the updates (process always executes on the EDT).

progressBar = new JProgressBar();
sw = new SwingWorker<Boolean,Integer>() {
    protected Boolean doInBackground() throws Exception {
        // If any of the operations fail, return false to notify done() 
        // Do thing 1
        publish(25);  // 25% done
        // Do thing 2
        publish(50);  // 50% done
        // Do thing 3
        publish(75);  // 75% done
        // Do thing 4
        return true;
    }
    protected void process(List<Integer> chunks) {
        for (Integer i : chunks)
            progressBar.setValue(i);
    }
    protected void done() {
        try {
            boolean b = get();
            if (b)
                progressBar.setValue(100); // 100% done
            else
                // Notify the user processing failed
        }
        catch (InterruptedException ex) {
                // Notify the user processing was interrupted
        }
        catch (ExecutionException ex) {
                // Notify the user processing raised an exception
        }
    }
};

Addendum:

This can be extended to multiple tasks, it just requires changing how you approach setting the progress bar. Here's what comes to mind:

Have an array of completion counter, one per task.

int[] completions = new int[numTasks];
Arrays.fill(completions,0);

Start the SwingWorkers, each passed an index number. The process or done methods then call something like this to update the overall progress bar.

void update(int index, int percComplete) {
    completions[index] = percComplete;
    int total = 0;
    for(int comp: completions)
        total += comp/numTasks;
    overallPB.setValue(total);
}

Optionally, display a JProgressBar per task.

Addendum 2:

If the tasks vary in completion time (eg, cache hit vs cache miss), you may want to investigate ProgressMonitor. It's a progress dialog that only appears if the task takes more than some (configurable, default 500ms) amount of time.