Java JNA- Jar application hangs in 32 bit windows system

Question

Here's a screenshot application. Compiled with 1.8 JDK , works perfectly well in 64 bit systems, but lags and hangs in two iterations in 32 bit systems.

Basically this application takes a screenshot using robot class, takes the file name from user which is a URL. Truncates and removes all illegal characters from it and saves it using a save as dialog box with time-stamp as the prefix.

I am using Windows Low Level KeyHook to initiate the screenshot with PrtSc key.

Error in 32 bit systems: It only takes 2 screenshots and then does not respond when I press PrtSc for the 3rd time. Can JFrame cause any problems, it certainly loads up slow . Should I use any alternate text box than JFrame or is it because I have complied in java 1.8 jdk 64 bit environment, which wont work in lower versions of jdk or 32 bit systems.

public class KeyHook {
private static HHOOK hhk;
private static LowLevelKeyboardProc keyboardHook;
static JFileChooser fileChooser = new JFileChooser();
public static void main(String[] args) {
    final User32 lib = User32.INSTANCE;
    HMODULE hMod = Kernel32.INSTANCE.GetModuleHandle(null);
    keyboardHook = new LowLevelKeyboardProc() {
        public LRESULT callback(int nCode, WPARAM wParam, KBDLLHOOKSTRUCT info) {
            if (nCode >= 0) {
                switch(wParam.intValue()) {
                case WinUser.WM_KEYUP:
                case WinUser.WM_KEYDOWN:
                case WinUser.WM_SYSKEYUP:
                case WinUser.WM_SYSKEYDOWN:

                 if (info.vkCode == 44) { 


                        try {

                            Robot robot = new Robot();
                            // Capture the screen shot of the area of the screen defined by the rectangle
                             BufferedImage bi=robot.createScreenCapture(new Rectangle(0,25,1366,744));

                             JFrame frame = new JFrame();
                             JFrame.setDefaultLookAndFeelDecorated(true);
                             frame.toFront();
                             frame.requestFocus();
                             frame.setAlwaysOnTop(true);
                             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                             // prompt the user to enter their name
                             String name = JOptionPane.showInputDialog(frame, "Enter file name");
                            // frame.pack();

                             frame.dispose();
                             String fileName= dovalidateFile(name);

                             FileNameExtensionFilter filter = new FileNameExtensionFilter("PNG", ".png");
                               fileChooser.setFileFilter(filter);
                             fileChooser.setSelectedFile(new File (fileName));


                             int returnVal = fileChooser.showSaveDialog(null);
                             if ( returnVal == JFileChooser.APPROVE_OPTION ){

                                File file = fileChooser.getSelectedFile();


                                 file = validateFile(file);
                                 System.out.println(file);
                                 ImageIO.write(bi, "png", file);

                             }



                      }
                        catch (NullPointerException e1)
                        {e1.printStackTrace(); }
                        catch (AWTException e1) {
                            e1.printStackTrace();
                        } catch (IOException e1) {
                            e1.printStackTrace();
                        }
                    }
                    }
                }

            return lib.CallNextHookEx(hhk, nCode, wParam, info.getPointer());
        }

        private File validateFile(File file) {
            DateFormat dateFormat = new SimpleDateFormat("HH.mm.ss.ddMMMMMyyyy");
               //get current date time with Calendar()
               Calendar cal = Calendar.getInstance();
              // System.out.println(dateFormat.format(cal.getTime()));
            String filePath = file.getAbsolutePath();

            if (filePath.indexOf(".png") == -1) {
                filePath += "." + dateFormat.format(cal.getTime()) + ".png";
            }
            //System.out.println("File Path :" + filePath);
            file = new File(filePath);
            if (file.exists()) {
                file.delete();
            }
            try {
                file.createNewFile();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return file;

                    }

        private String dovalidateFile(String name) {

            String input = name.replace("https://www.","");  
            input = input.replaceAll("http://www.","");   
            input = input.replaceAll("https://","");    
            input = input.replace("http://","");
            input = input.replace("/?",".");
            input = input.replace("/",".");
            input = input.replace("|",".") ;
            input = input.replace("%",".");
            input = input.replace("<",".");
            input = input.replace(">",".");
            input = input.replaceAll("\\?",".");
            input = input.replaceAll("\\*",".");
            input = input.replace(":",".");
            input = input.replace("\\",".");
            input = Character.toUpperCase(input.charAt(0)) + input.substring(1);
            return input;
        } 
    };
    hhk = lib.SetWindowsHookEx(WinUser.WH_KEYBOARD_LL, keyboardHook, hMod, 0);

    if(!SystemTray.isSupported()){
        return ;
    }
    SystemTray systemTray = SystemTray.getSystemTray();
    Image image = Toolkit.getDefaultToolkit().getImage(KeyHook.class.getResource("/images/icon.png"));

    //popupmenu
    PopupMenu trayPopupMenu = new PopupMenu();

    MenuItem close = new MenuItem("Exit");
    close.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.err.println("unhook and exit");
            lib.UnhookWindowsHookEx(hhk);
            System.exit(0);

        }
    });
    trayPopupMenu.add(close);

    //setting tray icon
    TrayIcon trayIcon = new TrayIcon(image, "captur", trayPopupMenu);
    //adjust to default size as per system recommendation 
    trayIcon.setImageAutoSize(true);

    try{
        systemTray.add(trayIcon);
    }catch(AWTException awtException){
        awtException.printStackTrace();
    }

    int result;
    MSG msg = new MSG();
    while ((result = lib.GetMessage(msg, null, 0, 0)) != 0) {
        if (result == -1) {
            System.err.println("error in get message");
            break;
        }
        else {
            System.err.println("got message");
            lib.TranslateMessage(msg);
            lib.DispatchMessage(msg);
        }
      }
         lib.UnhookWindowsHookEx(hhk);

    }
 }

Answer 1

I don't have any experience with JNA, but there are several things that are wrong about your code - I don't think I got them all, but here are some:

1.  close.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { System.exit(0); quit=true; } }); 

   The quit=true will never be reached because your program exit() s before it ever goes there.

2.

     new Thread() {
         public void run() {
             while (!quit) {
                 try { Thread.sleep(10); } catch(Exception e) { }
             }
             System.err.println("unhook and exit");
             lib.UnhookWindowsHookEx(hhk);
             System.exit(0);
         }
     }.start();

doesn't make any sense since quit will never be true . Also spinning on a variable to detect a change will severly slow down your application (espacially with sleep-times of 10 ms). Why not do the unhook in your ActionListener ?

3.

    while ((result = lib.GetMessage(msg, null, 0, 0)) != 0) {

Here I'm not too sure because I don't have experience with JNA and the windows event system. The method waits for messages sent to the specified window, but since you don't specify any (second parameter is null ) I don't think you will ever get one.

4. For each callback you are creating a new JFrame but at the end of the method you are only hiding it using frame.setVisible(false); . Since it is still referenced from various Swing-classes it will never be garbage-collected. This creates a memory-leak which will slow down your application. You will have to call frame.dispose() to get rid of it.