Linux上的Java Keylistener

Question

I'm trying to write a game in java3d on Linux and for that I need a proper KeyListener. Did anyone of you know how to do it? I'm currently using following code, I found somewhere on the net. It's working pretty good, holding down just one key, but as soon, as I press more than one (like space and w) it will do unexpected things...

public class RepeatingReleasedEventsFixer implements AWTEventListener {

    private final HashMap<Integer, ReleasedAction> _map = new HashMap<Integer, ReleasedAction>();

    public void install() {
        Toolkit.getDefaultToolkit().addAWTEventListener(this, AWTEvent.KEY_EVENT_MASK);
    }

    public void remove() {
        Toolkit.getDefaultToolkit().removeAWTEventListener(this);
    }

    @Override
    public void eventDispatched(AWTEvent event) {
        assert event instanceof KeyEvent : "Shall only listen to KeyEvents, so no other events shall come here";
        assert assertEDT(); // REMEMBER THAT THIS IS SINGLE THREADED, so no need for synch.

        // ?: Is this one of our synthetic RELEASED events?
        if (event instanceof Reposted) {
            // -> Yes, so we shalln't process it again.
            return;
        }

        // ?: KEY_TYPED event? (We're only interested in KEY_PRESSED and KEY_RELEASED).
        if (event.getID() == KeyEvent.KEY_TYPED) {
            // -> Yes, TYPED, don't process.
            return;
        }

        final KeyEvent keyEvent = (KeyEvent) event;

        // ?: Is this already consumed?
        // (Note how events are passed on to all AWTEventListeners even though a previous one consumed it)
        if (keyEvent.isConsumed()) {
            return;
        }

        // ?: Is this RELEASED? (the problem we're trying to fix!)
        if (keyEvent.getID() == KeyEvent.KEY_RELEASED) {
            // -> Yes, so stick in wait
            /**
             * Really just wait until "immediately", as the point is that the subsequent PRESSED shall already have been
             * posted on the event queue, and shall thus be the direct next event no matter which events are posted
             * afterwards. The code with the ReleasedAction handles if the Timer thread actually fires the action due to
             * lags, by cancelling the action itself upon the PRESSED.
             */
            final Timer timer = new Timer(2, null);
            ReleasedAction action = new ReleasedAction(keyEvent, timer);
            timer.addActionListener(action);
            timer.start();

            _map.put(Integer.valueOf(keyEvent.getKeyCode()), action);

            // Consume the original
            keyEvent.consume();
        }
        else if (keyEvent.getID() == KeyEvent.KEY_PRESSED) {
            // Remember that this is single threaded (EDT), so we can't have races.
            ReleasedAction action = _map.remove(Integer.valueOf(keyEvent.getKeyCode()));
            // ?: Do we have a corresponding RELEASED waiting?
            if (action != null) {
                // -> Yes, so dump it
                action.cancel();
            }
            // System.out.println("PRESSED: [" + keyEvent + "]");
        }
        else {
            throw new AssertionError("All IDs should be covered.");
        }
    }

    /**
     * The ActionListener that posts the RELEASED {@link RepostedKeyEvent} if the {@link Timer} times out (and hence the
     * repeat-action was over).
     */
    private class ReleasedAction implements ActionListener {

        private final KeyEvent _originalKeyEvent;
        private Timer _timer;

        ReleasedAction(KeyEvent originalReleased, Timer timer) {
            _timer = timer;
            _originalKeyEvent = originalReleased;
        }

        void cancel() {
            assert assertEDT();
            _timer.stop();
            _timer = null;
            _map.remove(Integer.valueOf(_originalKeyEvent.getKeyCode()));
        }

        @Override
        public void actionPerformed(@SuppressWarnings ("unused") ActionEvent e) {
            assert assertEDT();
            // ?: Are we already cancelled?
            // (Judging by Timer and TimerQueue code, we can theoretically be raced to be posted onto EDT by TimerQueue,
            // due to some lag, unfair scheduling)
            if (_timer == null) {
                // -> Yes, so don't post the new RELEASED event.
                return;
            }
            // Stop Timer and clean.
            cancel();
            // Creating new KeyEvent (we've consumed the original).
            KeyEvent newEvent = new RepostedKeyEvent((Component) _originalKeyEvent.getSource(),
                    _originalKeyEvent.getID(), _originalKeyEvent.getWhen(), _originalKeyEvent.getModifiers(),
                    _originalKeyEvent.getKeyCode(), _originalKeyEvent.getKeyChar(), _originalKeyEvent.getKeyLocation());
            // Posting to EventQueue.
            Toolkit.getDefaultToolkit().getSystemEventQueue().postEvent(newEvent);
            // System.out.println("Posted synthetic RELEASED [" + newEvent + "].");
        }
    }

    /**
     * Marker interface that denotes that the {@link KeyEvent} in question is reposted from some
     * {@link AWTEventListener}, including this. It denotes that the event shall not be "hack processed" by this class
     * again. (The problem is that it is not possible to state "inject this event from this point in the pipeline" - one
     * have to inject it to the event queue directly, thus it will come through this {@link AWTEventListener} too.
     */
    public interface Reposted {
        // marker
    }

    /**
     * Dead simple extension of {@link KeyEvent} that implements {@link Reposted}.
     */
    public static class RepostedKeyEvent extends KeyEvent implements Reposted {
        public RepostedKeyEvent(@SuppressWarnings ("hiding") Component source, @SuppressWarnings ("hiding") int id,
                long when, int modifiers, int keyCode, char keyChar, int keyLocation) {
            super(source, id, when, modifiers, keyCode, keyChar, keyLocation);
        }
    }

    private static boolean assertEDT() {
        if (!EventQueue.isDispatchThread()) {
            throw new AssertionError("Not EDT, but [" + Thread.currentThread() + "].");
        }
        return true;
    }
}

I can't be the only one who still runs into this - meanwhile 15 yo - problem and don't want to use timers...

EDIT: What this code is doing is fix the known problem on any Linux distri, where you add a simple KeyListener, which handles keyDowns, but invokes keyReleased Event repeatedly. To clearify my problem here a simple example

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;

public class Test5 extends JFrame{

    public Test5() {
        addKeyListener(new KeyListener() {
            boolean keydown = false;
            @Override
            public void keyTyped(KeyEvent arg0) {
                // TODO Auto-generated method stub

            }

            @Override
            public void keyReleased(KeyEvent arg0) {
                keydown = false;
                System.out.println("keyup");
            }

            @Override
            public void keyPressed(KeyEvent arg0) {
                if (keydown){
                    System.out.println("key is down");
                } else {
                    System.out.println("key not down");
                }
                keydown = true;
            }
        });

        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(400, 400);
        setVisible(true);
        //new RepeatingReleasedEventsFixer().install(); // This line will fix it for one key pressed
    }
    public static void main(String[] args) {
        new Test5();
    }

}

The output without the line being commented out:

key not down
keyup
key not down
keyup
key not down
keyup
key not down
keyup
key not down
keyup

otherwise:

key not down
key is down
key is down
key is down
key is down
key is down
key is down
key is down
key is down
key is down
keyup

Btw. How come, that it's not beeing fixed by now?

EDIT: I tried the KeyBindings, as suggested, where it comes to these problems:

public class Test5 extends JFrame{
    long timestamp = 0;
    public Test5() {
        ((JComponent)getComponent(0)).getInputMap().put(KeyStroke.getKeyStroke('a'), "a");
        ((JComponent)getComponent(0)).getActionMap().put("a", new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("time: "+(System.currentTimeMillis()-timestamp));
                timestamp = System.currentTimeMillis();
            }
        });

        ((JComponent)getComponent(0)).getInputMap().put(KeyStroke.getKeyStroke('s'), "s");
        ((JComponent)getComponent(0)).getActionMap().put("s", new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("s");
            }
        });

        ((JComponent)getComponent(0)).getInputMap().put(KeyStroke.getKeyStroke('d'), "d");
        ((JComponent)getComponent(0)).getActionMap().put("d", new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                System.out.println("d");
            }
        });
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(400, 400);
        setVisible(true);
        new RepeatingReleasedEventsFixer().install(); // This line will fix it for one key pressed
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        new Test5();
    }

Holding down "a" will give me following output:

time: 4171
time: 501
time: 30
time: 30
time: 30

Where the second time is the actual problem. It takes about 470ms too long.
Holding down "s" and then somewhne pressing "d" will give me that output:

s
s
s
s
d
d
d
d
d

So I can't process two actions as the same time, so I can't use KeyBindings

Answer 1

This is not an answer, it is a long comment with a picture and some explanations.

I used your Test5 (without RepeatingReleasedEventsFixer ) to hold down a and measure the time responses. The output is of the form

time: t1
time: t2
time: t3
time: t3
time: t3
...

t1 is meaningless since it depends on the current time and has nothing to do with response time (you also seem to ignore it).

t2 is the time it takes for the OS to realize that you're holding the key for repeated input.

t3 is the "sample time" of the held key, or a discretization of the input.

I'm using Windows where I have the following control panel options:

Repeat delay allows me to set t2 between ~257 (short) and ~1050 (long).

Repeat rate allows me to set t3 between ~407 (slow) and ~37 (fast).

For Linux, you'll have to consult someone / somewhere on how to change these values if you don't already know how to.

As for using multiple keys, see this question and answer and the excellent link within (especially the "Motion With Multiple Keys Pressed" section). It's a short tutorial and analysis of key bindings and key listeners, similar to the one I sent you to on this site.

Key bindings will always be preferred over key listeners unless maybe there is some very low level thing you want to do.

Answer 2

After days of researching and putting stuff together, I ended up writing my own Listener combined with a KeyEventDispatcher, here is the code for someone running into the same problem. It can and should be optimized, but is working for now:

Klass to test if a specific key is pressed:

import java.awt.KeyEventDispatcher;
import java.awt.KeyboardFocusManager;
import java.awt.event.KeyEvent;
import java.util.HashMap;


public class IsKeyPressed {
    private static boolean wPressed = false;
    private HashMap<Integer, Boolean> keys = new HashMap<Integer, Boolean>();
    public IsKeyPressed() {
        KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(new KeyEventDispatcher() {

            @Override
            public boolean dispatchKeyEvent(KeyEvent ke) {
                synchronized (IsKeyPressed.class) {
                    switch (ke.getID()) {
                    case KeyEvent.KEY_PRESSED:
                        keys.put(ke.getKeyCode(), true);
                        break;

                    case KeyEvent.KEY_RELEASED:
                        keys.put(ke.getKeyCode(), false);
                        break;
                    }
                    return false;
                }
            }
        });
    }
    public static boolean isWPressed() {
        synchronized (IsKeyPressed.class) {
            return wPressed;
        }
    }

    public boolean isPressed(int keyCode){
        synchronized (IsKeyPressed.class) {
            if (keys == null)
                return false;
            if (keys.get(keyCode) == null)
                return false;
            return keys.get(keyCode);
        }
    }

}

Abstract class, thats beeing used for the actions.

public abstract class KeyActionListener {
    protected int keyCode;
    public KeyActionListener(int keyCode) {
        this.keyCode = keyCode;
    }
    public void setKeyCode(int keyCode){
        this.keyCode = keyCode;
    }
    public int getKeyCode(){
        return this.keyCode;
    }
    public abstract void onKeyDown();
    public abstract void onKeyUp();
    public abstract void onKeyHolding();
}

Start listening to the keys and run the actions.

import java.util.ArrayList;
import java.util.HashMap;

public class KeyThread extends Thread{
    private int sleep = 3;
    ArrayList<KeyActionListener> listener = new ArrayList<KeyActionListener>();
    IsKeyPressed isPressed = new IsKeyPressed();
    HashMap<KeyActionListener, Boolean> pressed = new HashMap<KeyActionListener, Boolean>();
    public KeyThread() {
        this.start();
    }
    public void run() {
        while (true){
            for (int i = 0; i < listener.size(); i++) {
                KeyActionListener curListener = listener.get(i);
                if (isPressed.isPressed(curListener.getKeyCode()) && !pressed.get(curListener)){
                    curListener.onKeyDown();
                    pressed.put(curListener, true);
                } else if(!isPressed.isPressed(curListener.getKeyCode()) && pressed.get(curListener)) {
                    curListener.onKeyUp();
                    pressed.put(curListener, false);
                } 

                if(isPressed.isPressed(curListener.getKeyCode())){
                    curListener.onKeyHolding();
                }
                try{
                    Thread.sleep(sleep);
                } catch(InterruptedException e){

                }
            }
        }
    }

    public void addKeyActionListener(KeyActionListener l){
        listener.add(l);
        pressed.put(l, false);
    }

}