Why simulating Control_A with Robot in Java is not working?

Question

I use the following lines to simulate a Control_A [ select all ] key action in Java with robot, but the clipboard is not getting the text, why ?

        Robot robot=null;
        try { robot=new Robot(); }
        catch (AWTException ex) { System.err.println("Can't start Robot: " + ex); }
        robot.mouseMove(260,500);
        robot.mousePress(InputEvent.BUTTON1_MASK);
//        robot.mouseMove(660,700);
        robot.mouseRelease(InputEvent.BUTTON1_MASK);

        robot.keyPress(KeyEvent.VK_CONTROL);              // Select all
        robot.keyPress(KeyEvent.VK_A);
        robot.keyRelease(KeyEvent.VK_A);
        robot.keyRelease(KeyEvent.VK_CONTROL);

        robot.keyPress(KeyEvent.VK_CONTROL);              // Copy
        robot.keyPress(KeyEvent.VK_C);
        robot.keyRelease(KeyEvent.VK_C);
        robot.keyRelease(KeyEvent.VK_CONTROL);

        Transferable t=Toolkit.getDefaultToolkit().getSystemClipboard().getContents(null);
        try
        {
          if (t!=null && t.isDataFlavorSupported(DataFlavor.stringFlavor))
          {
            String text=(String)t.getTransferData(DataFlavor.stringFlavor);
            System.out.println(text);
          }
        }
        catch (Exception ex) { ex.printStackTrace(); }

I have a browser open so at [260,500] on screen there is text at that area. What have I missed ?

Edit:

I just found something strange, when I opened a browser, the text in the browser is not copies, but if I open a notepad/wordpad, the text in them will be copies, so why the browser didn't do it ?

Answer 1

1. All of your code should be inside the try block where you instantiate the Robot because you could end up trying to work with a null reference and get a NullPointerException. And if your Robot never got created and never copied contents, there'd be no point in you trying to access the contents from the clipboard either.

2. I'm not entirely sure why but adding a small delay before trying to read from the clipboard fixes things. I'm guessing it might have to do with a race condition between Java getting hold of the clipboard before the system has had time to update it.

This updated code should work:

Robot robot = null;
try
{
    robot = new Robot();
    robot.mouseMove(260, 500);
    robot.mousePress(InputEvent.BUTTON1_MASK);
    // robot.mouseMove(660,700);
    robot.mouseRelease(InputEvent.BUTTON1_MASK);

    robot.keyPress(KeyEvent.VK_CONTROL); // Select all
    robot.keyPress(KeyEvent.VK_A);
    robot.keyRelease(KeyEvent.VK_A);
    robot.keyRelease(KeyEvent.VK_CONTROL);

    robot.keyPress(KeyEvent.VK_CONTROL); // Copy
    robot.keyPress(KeyEvent.VK_C);
    robot.keyRelease(KeyEvent.VK_C);
    robot.keyRelease(KeyEvent.VK_CONTROL);

    try
    {
        //sleep just a little to let the clipboard contents get updated
        Thread.sleep(25);
    }
    catch (InterruptedException e)
    {
        e.printStackTrace();
    }

    Transferable t = Toolkit.getDefaultToolkit().getSystemClipboard().getContents(null);
    try
    {
        if (t != null && t.isDataFlavorSupported(DataFlavor.stringFlavor))
        {
            String text = (String) t.getTransferData(DataFlavor.stringFlavor);
            System.out.println(text);
        }
    }
    catch (Exception ex)
    {
        ex.printStackTrace();
    }
}
catch (AWTException ex)
{
    System.err.println("Can't start Robot: " + ex);
}