Java Swing - 如何当用户在JDialog外部单击时关闭模式JDialog

import java.awt.BorderLayout;
import java.awt.Frame;
import java.awt.event.WindowEvent;
import java.awt.event.WindowFocusListener;

import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;

public class Main extends JDialog {
  public Main(final Frame owner) {
    super(owner);
    JPanel pnl = new JPanel(new BorderLayout());
    pnl.add(new JLabel("Click outside this dialog in the parent frame to close it"),
        BorderLayout.NORTH);
    JButton btn = new JButton("Click Me");
    btn.addActionListener(e -> JOptionPane.showMessageDialog(Main.this,
        "New Child Window"));
    pnl.add(btn, BorderLayout.CENTER);
    this.setContentPane(pnl);
    this.pack();
    this.setLocationRelativeTo(owner);
    this.setAlwaysOnTop(true);
    this.addWindowFocusListener(new WindowFocusListener() {
      public void windowGainedFocus(WindowEvent e) {
      }
      public void windowLostFocus(WindowEvent e) {
        if (SwingUtilities.isDescendingFrom(e.getOppositeWindow(), Main.this)) {
          return;
        }
        Main.this.setVisible(false);
      }
    });
  }
  public static void main(String[] args) {
    JFrame parent = new JFrame();
    parent.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    parent.setSize(300, 300);
    parent.setVisible(true);
    Main dlg = new Main(parent);
    dlg.setVisible(true);
  }
}