Closing a Swing App with Window Closing Event With Dialogs On Close

Question

A while back I started a thread discussing how to neatly close a Swing app using both the standard window "X" button and a custom action such as a File menu with an Exit menu item. Ultimately, I came to the conclusion that the cleanest solution in many cases is to use a default close operation of JFrame.EXIT_ON_CLOSE and in any custom actions manually fire a WindowEvent with WindowEvent.WINDOW_CLOSING. Using this strategy, both the "X" button and the custom action act in the same manner and can be successfully intercepted by listening for a window closing event if any cleanup is required; furthermore, the cleanup could use dialogs to prompt for user actions without any ill effects.
I did, however, encounter one oddity that I mentioned in the previous thread. A dialog launched through SwingUtilities.invokeLater in the cleanup method would cause the app to not shutdown. This is somewhat of an academic curiosity as I am not sure you would ever have a rational need to do this, but I thought it would be interesting to explore more fully. Here is a complete example that demonstrates; see what you think:
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class CloseByWindowClosingTest {
     public static void main(String[] args) {
          SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    launchGUI();
     private static void launchGUI() {
          final JFrame frame = new JFrame("Close By Window Closing Test");
          JPanel panel = new JPanel();
          panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
          JButton button1 = new JButton("No Dialog Close");
          JButton button2 = new JButton("Dialog On Close");
          JButton button3 = new JButton("Invoke Later Dialog On Close");
          button1.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    postWindowClosingEvent(frame);
          button2.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    JOptionPane.showMessageDialog(frame, "Test Dialog");
                    postWindowClosingEvent(frame);
          button3.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    SwingUtilities.invokeLater(new Runnable() {
                         public void run() {
                              JOptionPane.showMessageDialog(frame, "Test Dialog");
                    postWindowClosingEvent(frame);
          panel.add(button1);
          panel.add(button2);
          panel.add(button3);
          frame.setContentPane(panel);
          frame.pack();
          frame.setLocationRelativeTo(null);
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frame.addWindowListener(new WindowAdapter() {
               @Override
               public void windowClosing(WindowEvent event) {
                    System.out.println("Received Window Closing Event");
          frame.setVisible(true);
     private static void postWindowClosingEvent(JFrame frame) {
          WindowEvent windowClosingEvent = new WindowEvent(frame, WindowEvent.WINDOW_CLOSING);
          frame.getToolkit().getSystemEventQueue().postEvent(windowClosingEvent);
}An additional note not in the example -- if in the button 3 scenario you were to put the window closing event posting inside the invoke later, the app then again closes. However, as implemented, what is it that causes button 3 to not result in the application closing?
Edited by: Skotty on Aug 11, 2009 5:08 PM -- Modified example code -- added the WindowAdapter to the frame as a window listener to show which buttons cause listeners to receive the window closing event.

Answer 1

I'm not sure I understand why any "cleanup" code would need to use SwingUtilities.invokeLater() to do anything. Assuming this "cleanup method" was called in response to a WindowEvent, it's already being called on the EDT.
IIRC, my approach to this "problem" was to set the JFrame to DO_NOTHING_ON_CLOSE. I create a "doExit()" method that does any cleanup and exits the application (and possibly allows the user to cancel the app closing, if so desired). Then I create a WindowListener that calls doExit() on windowClosingEvents, and have my "exit action" call doExit() as well. Seems to work fine for me.