Use Java to lock a screen

Question

Basically i just need to create an application (with sort of user access) which first screen is a fullscreen window that cannot be minimized or closed without entering valid username and password. Something like windows screensaver. Can it be done? What libraries should i look into? This is all i need, if my question is incomplete or unclear, feel free to ask!

Answer 1

In any half-decent OS, the OS will be the one in charge of assigning an area or window to each process.

You will need to check each OS method of doing that, and implement it in native code (probably C or C++) using JNI.

Answer 2

Once, I wrote something in Java, out of which you can't escape. Really impossible. It is for Windows. Here you go:

import java.awt.Robot;
import javax.swing.JFrame;


public class WindowsSecurity implements Runnable 
{
  private JFrame frame;
  private boolean running;

  public WindowsSecurity(JFrame yourFrame)
  {
    this.frame = yourFrame;
    new Thread(this).start();
  }

  public void stop()
  {
     this.running = false;
  }

  public void run() {
    try {
      this.terminal.getParentFrame().setAlwaysOnTop(true);
      this.terminal.getParentFrame().setDefaultCloseOperation(0);
      kill("explorer.exe"); // Kill explorer
      Robot robot = new Robot();
      int i = 0;
      while (running) {
         sleep(30L);
         focus();
         releaseKeys(robot);
         sleep(15L);
         focus();
         if (i++ % 10 == 0) {
             kill("taskmgr.exe");
         }
         focus();
         releaseKeys(robot);
      }
      Runtime.getRuntime().exec("explorer.exe"); // Restart explorer
    } catch (Exception e) {

    }
  }

  private void releaseKeys(Robot robot) {
    robot.keyRelease(17);
    robot.keyRelease(18);
    robot.keyRelease(127);
    robot.keyRelease(524);
    robot.keyRelease(9);
  }

  private void sleep(long millis) {
    try {
      Thread.sleep(millis);
    } catch (Exception e) {

    }
  }

  private void kill(String string) {
    try {
      Runtime.getRuntime().exec("taskkill /F /IM " + string).waitFor();
    } catch (Exception e) {
    }
  }

  private void focus() {
    this.frame.grabFocus();
    this.frame.requestFocus();
  }
}

Background of this code: I wrote some kind of fake terminal in which I could let appear everything what I wanted. Eg, the stupid Windows messages like: "Keyboard not found, press any key to continue". I used it as a joke on school. Fire up this app and leave the room, it would log out the Windows account automatically after one minute. But I hadn't thought that there would be a teacher that used Ctrl-Alt-Del to kill my application. He left a message in my personal documents in which he wrote what he did and ended his message with "I've beaten you, haha I'm evil". So, I wanted to go in competition with him. And then wrote this code. He tried more than five times in school to escape from the app, but he couldn't (I can't as well :D). Of course he could turn off the machine or log out. But the target was to access my personal documents.