Window#toFront() does not activate JFrame

Question

Hello,
I noticed that the method "Window#toFront()" is not enough to activate a JFrame that is hidden behind other windows/applications. So I imagined the following hack, but wonder if anyone knows about a better way:
private Robot r;
        try {
            r = new Robot();
        } catch (AWTException ex) {
            ex.printStackTrace();
private void activateWindow(JFrame frame) {
    frame.setAlwaysOnTop(true);
    frame.setAlwaysOnTop(false);
    Point location = MouseInfo.getPointerInfo().getLocation();
    Point locationOnScreen = frame.getLocationOnScreen();
    r.mouseMove(locationOnScreen.x+100, locationOnScreen.y+10);
    r.mousePress(InputEvent.BUTTON1_MASK);
    r.mouseRelease(InputEvent.BUTTON1_MASK);
    r.mouseMove(location.x, location.y);
}The functionality is needed when clicking an icon in the notification area of the task bar. This should start the swing application only once. When the icon is clicked again, the started application should always activate its main window.
Regards,
André

Answer 1

class SingleInstanceController {
    private boolean result = false;
    private File file = null;
    private ObjectOutputStream oos = null;
    private ObjectInputStream ois = null;
    private ServerSocket server = null;
    private Socket client = null;
    private ArrayList<ApplicationStartedListener> listener = null;
    private String appname = null;
    public SingleInstanceController(File file, String appname) {
        this.file = file;
        this.appname = appname;
        this.listener = new ArrayList<ApplicationStartedListener>();
    public SingleInstanceController(String appname) {
        this(new File(System.getProperty("java.io.tmpdir") + "/923jhakE53Kk9235b43.6m7"), appname);
    public void addApplicationStartedListener(ApplicationStartedListener asl) {
        this.listener.add(asl);
    public void removeApplicationStartedListener(ApplicationStartedListener asl) {
        this.listener.remove(asl);
    public boolean isOtherInstanceRunning() {
        if (!this.file.exists()) {
            return false;
        return sendMessageToRunningApplication(new ClassCheck(this.appname));
    public boolean sendMessageToRunningApplication(final Object obj) {
        this.result = false;
        try {
            this.client = new Socket("localhost", getPortNumber());
            // In einem neuen Thread kommunizieren, um einen Deadlock zu verhindern
            new Thread(new Runnable() {
                public void run() {
                    try {
                        SingleInstanceController.this.oos = new ObjectOutputStream(SingleInstanceController.this.client.getOutputStream());
                        SingleInstanceController.this.ois = new ObjectInputStream(SingleInstanceController.this.client.getInputStream());
                        SingleInstanceController.this.oos.writeObject(obj);
                        SingleInstanceController.this.oos.flush();
                        SingleInstanceController.this.result = SingleInstanceController.this.ois.readBoolean();
                    } catch (IOException e) {
                        SingleInstanceController.this.result = false;
            }).start();
            for (int i = 0; i < 10; i++) {
                if (this.result == true) {
                    break;
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    e.printStackTrace();
            this.client.close();
            return this.result;
        } catch (IOException e) {
            return false;
    public boolean registerApplication() {
        try {
            if (!this.file.exists()) {
                if (!this.file.getParentFile().mkdirs() && !this.file.getParentFile().exists()) {
                    return false;
                if (!this.file.createNewFile()) {
                    return false;
            BufferedWriter wuffy = new BufferedWriter(new FileWriter(this.file));
            int port = getFreeServerSocket();
            if (port != -1) {
                startServer();
            wuffy.write(String.valueOf(port));
            wuffy.close();
            return true;
        } catch (IOException e) {
            return false;
    protected void messageArrived(Object obj) {
        for (ApplicationStartedListener asl : this.listener) {
            asl.messageArrived(obj);
    protected void applicationStartet() {
        for (ApplicationStartedListener asl : this.listener) {
            asl.applicationStarted();
    protected void foreignApplicationStarted(String name) {
        for (ApplicationStartedListener asl : this.listener) {
            asl.foreignApplicationStarted(name);
    private int getPortNumber() {
        try {
            BufferedReader buffy = new BufferedReader(new FileReader(this.file));
            int port = Integer.parseInt(buffy.readLine().trim());
            buffy.close();
            return port;
        } catch (Exception e) {
            return -1;
    private void startServer() {
        new Thread(new Runnable() {
            public void run() {
                while (true) {
                    try {
                        SingleInstanceController.this.client = SingleInstanceController.this.server.accept();
                        if (SingleInstanceController.this.client.getInetAddress().isLoopbackAddress()) {
                            new Thread(new Runnable() {
                                public void run() {
                                    try {
                                        SingleInstanceController.this.oos = new ObjectOutputStream(SingleInstanceController.this.client.getOutputStream());
                                        SingleInstanceController.this.ois = new ObjectInputStream(SingleInstanceController.this.client.getInputStream());
                                        Object obj = SingleInstanceController.this.ois.readObject();
                                        if (obj instanceof ClassCheck) {
                                            if (obj.toString().equals(SingleInstanceController.this.appname)) {
                                                SingleInstanceController.this.oos.writeBoolean(true);
                                                applicationStartet();
                                            } else {
                                                SingleInstanceController.this.oos.writeBoolean(false);
                                                foreignApplicationStarted(obj.toString());
                                        } else {
                                            messageArrived(obj);
                                            SingleInstanceController.this.oos.writeBoolean(true);
                                        SingleInstanceController.this.oos.flush();
                                        SingleInstanceController.this.client.close();
                                    } catch (IOException e) {
                                        e.printStackTrace();
                                    } catch (ClassNotFoundException e) {
                                        e.printStackTrace();
                            }).start();
                    } catch (IOException e) {
                        e.printStackTrace();
        }).start();
    private int getFreeServerSocket() {
        for (int i = 2000; i < 10000; i++) {
            try {
                this.server = new ServerSocket(i);
                return i;
            } catch (IOException ignore) {
        return -1;
}