Question

I’m working with javax.swing to make an aplication which generates forms from XML Schema (using JAXFront library) and stores the data filled by the user them into XML documents.

I have put try-catch-finally blocks when I need it, but I have a little problem catching exceptions when the main thread ends (The AWT threads are still running).

I have two classes which do the main work and other classes which aren’t important for the question:

• Main class: It has the following structure. Initializes the application and runs the main frame

  public class Main { 
      public static void main(String[] args) {
          readArgs(); // An INI file with the app config
          Model model = initializeElements(args); // My model class
          try {
              MyFrame mfr = new MyFrame(title,model);
              mfr.visualize(); // Assembling view and setting visible
          } catch( Excepion e ) {
              doCleanUp();
              System.exit(-1);
          }
      }
  }

• Frame Class: Generates the view and listen events

  public class MyFrame extends JFrame implements ActionListener,MenuListener { 
      // Some attributes
      // Other mthods without importance
      /**
       * Compose the elements, add listeners and set visible the frame
       */
      public void visualize() {
          generateFormPanel();
          setListeners();
          validate();
          setVisible(true);
      }
  
      public MyFrame(String title, Modele model) {
          super(title);
          createElementsUsing(model);
      }
  
      public void actionPerformed(ActionEvent e) {
          // Code to manage events
      }
  }

Well, the problem is the following:
When the visualize function is exectuted from the main method, the view is generated and showed. At that moment is when I lose the control of the exceptions catching. Then my question is if there are some way to catch the possible RuntimeExceptions throwed after this point.

I hope you understand my English and can answer the question.

Thanks in advance.

Answer 1

Simplest version is to set the default uncaught exception handler:

Thread.setDefaultUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
    public void uncaughtException(Thread t, Throwable e) {
        // do something
    }
});

But that catches uncaught exceptions thrown in other parts of the program aswell.

You could however catch only runtime exceptions thrown off the swing event dispatching thread using a proxy (See this page for more information, copied code from there):

class EventQueueProxy extends EventQueue {

    protected void dispatchEvent(AWTEvent newEvent) {
        try {
            super.dispatchEvent(newEvent);
        } catch (Throwable t) {
            // do something more useful than: t.printStackTrace();
        }
    }
}

Now installing it like this:

Toolkit.getDefaultToolkit().getSystemEventQueue().push(new EventQueueProxy());