Graceful exception handling in Swing Worker

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I am using threading in application through Swing Worker class. It works fine, yet I have a bad feeling about showing an error message dialog in try-catch block. Can it potentially block the application? This is what it looks right now:

SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {

    // Executed in background thread
    public Void doInBackground() {
        try {
            DoFancyStuff();
        } catch (Exception e) {

            e.printStackTrace();

            String msg = String.format("Unexpected problem: %s", e
                    .toString());

            //TODO: executed in background thread and should be executed in EDT?
            JOptionPane.showMessageDialog(Utils.getActiveFrame(),
                    msg, "Error", JOptionPane.ERROR_MESSAGE,
                    errorIcon);

        }//END: try-catch

        return null;
    }

    // Executed in event dispatch thread
    public void done() {
        System.out.println("Done");
    }
};

Can it be done in a safe way using Swing Worker framework? Is overriding publish() method a good lead here?

EDIT:

Did it like this:

} catch (final Exception e) {

    SwingUtilities.invokeLater(new Runnable() {

        public void run() {

            e.printStackTrace();

            String msg = String.format(
                    "Unexpected problem: %s", e.toString());

            JOptionPane.showMessageDialog(Utils
                    .getActiveFrame(), msg, "Error",
                    JOptionPane.ERROR_MESSAGE, errorIcon);

        }
    });

}

Calling get in done method would result in two try-catch blocks, as the computational part throws exceptions, so I think this is cleaner in the end.

swing exception-handling java
4 Answers

First of all: sorry for the short answer, don't have too much time to spare.

I had the same problem: wanting to publish to System.out from within the worker.

Short answer: It won't block your app if you use the execute() method

The thing is that there is no blocking if you execute the worker as it should be: a background task.

class MyWorker extend SwingWorker<Void, Void>{
  @Override
  protected Void doInBackground() throws ... {
    // your logic here and a message to a stream
    System.out.println("from my worker, with love");
    // ...
    try { 
      throw new Exception("Whoops, this is an exception from within the worker"); 
    } catch (Exception e) { 
      System.out.println(e.getMessage()); 
    }
  }
}

Now you will invoke this worker creating a new instance, and after that calling the execute() method. But to save you some time: you will probably want to know when your worker is done, so you'll need to register an property change listener, which is fairly simple:

class MyListener implements PropertyChangeListener{
  @Override
  public void propertyChange(PropertyChangeEvent evt){
    if(evt.getPropertyName().equals("state") && evt.getNewValue().equals(SwingWorker.StateValue.DONE)){
        System.out.println("The worker is done");
    }
  }
}

And to put everything together at your main():

public void main(...){
  MyWorker w = new MyWorker();
  MyListener l = new MyListener();
  w.addPropertyChangeListener(l);
  w.execute();
}
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