Does AWT/Swing cancel painting operations if the monitor is off?

I am experiencing a problem with Swing that only occurs when the computer monitor is powered off, but my Swing application continues to run in the background. It seems that whenever the monitor is off, Swing/AWT cancels all painting operations, leading to a number of display issues in the GUI that are visible as soon as the monitor turns back on.

For example, when I turn off the monitor using a custom JNI function and subsequently open a simple message dialog, the message dialog is blank when the monitor turns back on:

But it paints correctly after the next repaint:

Is this the expected behavior of Swing? Is there a way to instruct Swing to continue drawing to the screen even if the monitor is powered off?

EDIT: Here is an SSCCE:

package test;

import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

public class App {
    public static void main(String[] args) throws Throwable {
        System.out.println("***** Please turn off the monitor in the next 70 seconds *****");
        Thread.sleep(1000L * 70);

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JOptionPane.showMessageDialog(null, "Test");
            }
        });
    }
}

I am using 64-bit Windows 7 Home Premium SP1 and 64-bit Java 1.6.0_24.

EDIT 2: Here is another program with which I experience the effect of "canceled painting operations":

package test;

import static com.mycompany.Util.turnOffMonitors;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.Dimension;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;

public class DialogTest extends JDialog {
    private final JLabel label;

    public DialogTest() {
        setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);

        label = new JLabel("Test", JLabel.CENTER);
        label.setOpaque(true);

        Container contentPane = getContentPane();
        contentPane.setLayout(new BorderLayout());
        contentPane.add(BorderLayout.CENTER, label);

        this.setPreferredSize(new Dimension(200, 110));
        pack();
        setLocationRelativeTo(null);
        setVisible(true);

        Thread t = new Thread() {
            @Override
            public void run() {
                turnOffMonitors();
                try {
                    Thread.sleep(3000L);
                } catch (InterruptedException ex) { }

                SwingUtilities.invokeLater(new Runnable() {
                   @Override
                   public void run() {
                       label.setBackground(Color.YELLOW);
                   }
                });
            }
        };
        t.start();
    }

    public static void main(String[] args) throws Throwable {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new DialogTest();
            }
        });
    }
}

Before the monitor shuts off, I see:

With the monitor off, the label background color is changed to yellow in the background. I then move the mouse to turn the monitor back on. The dialog is visually unchanged. It is only after I force a repaint (by ALT-TABbing, for example) do I see the yellow:

EDIT 3: Reported to Oracle as Bug ID 7049597.

I then started the program and stopped moving the mouse/typing. After one minute, the screen turned off. I waited another 20 seconds to move the mouse. The monitor turned back on and I saw a blank message dialog.

Using your example, I don't see this on my (non-Windows) platform. You might try the example below, which should alternate between WINDOW_ACTIVATED on wake and WINDOW_DEACTIVATED on sleep. If so, you could extend JDialog and repaint() in windowActivated().

import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JLabel;

/** @see http://stackoverflow.com/questions/6163606 */
public class DialogEventTest extends JDialog {

    public DialogEventTest() {
        this.setLayout(new GridLayout(0, 1));
        this.add(new JLabel("Dialog event test.", JLabel.CENTER));
        this.add(new JButton(new AbstractAction("Close") {

            @Override
            public void actionPerformed(ActionEvent e) {
                DialogEventTest.this.setVisible(false);
                DialogEventTest.this.dispatchEvent(new WindowEvent(
                    DialogEventTest.this, WindowEvent.WINDOW_CLOSING));
            }
        }));
    }

    private static class WindowHandler extends WindowAdapter {

        @Override
        public void windowActivated(WindowEvent e) {
            System.out.println(e);
        }

        @Override
        public void windowDeactivated(WindowEvent e) {
            System.out.println(e);
        }
    }

    private void display() {
        this.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        this.addWindowListener(new WindowHandler());
        this.pack();
        this.setLocationRelativeTo(null);
        this.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new DialogEventTest().display();
            }
        });
    }
}

The problem probably has more to do with how it repaints when the screen comes on rather than what happens while it's off. You could check by running a screen recorder.

来源：https://stackoverflow.com/questions/6163606/does-awt-swing-cancel-painting-operations-if-the-monitor-is-off

标签

java

swing

awt

repaint