Enable Java Swing logging (key dispatch)

Question

I need to debug key event dispatch in a Swing application. I thought the following would be sufficient:

val eventLog = PlatformLogger.getLogger("java.awt.event.Component")
eventLog.setLevel(PlatformLogger.Level.ALL)
val focusLog = PlatformLogger.getLogger("java.awt.focus.DefaultKeyboardFocusManager")
focusLog.setLevel(PlatformLogger.Level.ALL)

But nothing happens. (the loggers report they are enabled, but I cannot see any text output). Do I need to configure a PrintStream somewhere to see the log messages?

Answer 1

As suggested here, I'm not sure that using sun.util.logging.PlatformLogger is appropriate. To log focus events, I had to specify a higher level on the root logger, e.g. Level.ALL. Adding a ConsoleHandler, like this, may make the log easier to read.

Console:

java.awt.focus.DefaultKeyboardFocusManager: sun.awt.TimedWindowEvent[WINDOW_GAINED_FOCUS,opposite=null,oldState=0,newState=0] on frame0
java.awt.focus.DefaultKeyboardFocusManager: java.awt.event.WindowEvent[WINDOW_ACTIVATED,opposite=null,oldState=0,newState=0] on frame0
java.awt.focus.DefaultKeyboardFocusManager: tempLost {0}, toFocus {1}
java.awt.focus.Component: focus owner is null or this
java.awt.focus.DefaultKeyboardFocusManager: Enqueue at {0} for {1}
java.awt.focus.Component: Pass for javax.swing.JButton[,0,0,97x29,alignmentX=0.0,alignmentY=0.5,border=com.apple.laf.AquaButtonBorder$Dynamic@56e325b9,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=2,bottom=0,right=2],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Button 1,defaultCapable=true]
java.awt.focus.DefaultKeyboardFocusManager: java.awt.event.WindowEvent[WINDOW_OPENED,opposite=null,oldState=0,newState=0] on frame0
java.awt.focus.DefaultKeyboardFocusManager: sun.awt.TimedWindowEvent[WINDOW_GAINED_FOCUS,opposite=javax.swing.JFrame[frame0,752,469,97x80,layout=java.awt.BorderLayout,title=LoggerTest,resizable,normal,defaultCloseOperation=EXIT_ON_CLOSE,rootPane=javax.swing.JRootPane[,0,22,97x58,layout=javax.swing.JRootPane$RootLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=16777673,maximumSize=,minimumSize=,preferredSize=],rootPaneCheckingEnabled=true],oldState=0,newState=0] on frame0
java.awt.focus.DefaultKeyboardFocusManager: java.awt.FocusEvent[FOCUS_GAINED,permanent,opposite=null,cause=ACTIVATION] on javax.swing.JButton[,0,0,97x29,alignmentX=0.0,alignmentY=0.5,border=com.apple.laf.AquaButtonBorder$Dynamic@56e325b9,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=2,bottom=0,right=2],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Button 1,defaultCapable=true]
java.awt.focus.DefaultKeyboardFocusManager: Markers before FOCUS_GAINED on {0}
java.awt.focus.DefaultKeyboardFocusManager: >>> Markers dump, time: {0}
java.awt.focus.DefaultKeyboardFocusManager:     {0}
java.awt.focus.DefaultKeyboardFocusManager: Markers after FOCUS_GAINED
java.awt.focus.DefaultKeyboardFocusManager: >>> Markers dump, time: {0}
java.awt.focus.Component: java.awt.FocusEvent[FOCUS_GAINED,permanent,opposite=null,cause=ACTIVATION] on javax.swing.JButton[,0,0,97x29,alignmentX=0.0,alignmentY=0.5,border=com.apple.laf.AquaButtonBorder$Dynamic@56e325b9,flags=288,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=javax.swing.plaf.InsetsUIResource[top=0,left=2,bottom=0,right=2],paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Button 1,defaultCapable=true]
java.awt.focus.DefaultKeyboardFocusManager: java.awt.event.WindowEvent[WINDOW_CLOSING,opposite=null,oldState=0,newState=0] on frame0

Code:

import java.awt.EventQueue;
import java.awt.GridLayout;
import java.util.logging.ConsoleHandler;
import java.util.logging.Formatter;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import java.util.logging.Logger;
import javax.swing.JButton;
import javax.swing.JFrame;

/**
 * @see https://stackoverflow.com/a/31223145/230513
 * @see https://stackoverflow.com/q/20815048/230513
 */
public class LoggerTest {

    private void display() {
        JFrame f = new JFrame("LoggerTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new GridLayout(0, 1));
        f.add(new JButton("Button 1"));
        f.add(new JButton("Button 2"));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        Logger rootLogger = Logger.getLogger("");
        rootLogger.setLevel(Level.ALL);
        logClass("java.awt.focus.Component");
        logClass("java.awt.focus.DefaultKeyboardFocusManager");
        EventQueue.invokeLater(new LoggerTest()::display);
    }

    private static void logClass(String name) {
        ConsoleHandler consoleHandler = new ConsoleHandler();
        consoleHandler.setLevel(Level.ALL);
        consoleHandler.setFormatter(new Formatter() {
            @Override
            public String format(LogRecord record) {
                return name + ": " + record.getMessage() + '\n';
            }
        });
        Logger logger = Logger.getLogger(name);
        logger.setLevel(Level.ALL);
        logger.addHandler(consoleHandler);
    }
}