Java (low-level) System Hook provides a very light-weight global keyboard and mouse listener for Java. Generally keyboard and mouse events in Java only work, if the registered component is in focus. For example, in case any window looses its focus (e.g. when minimized), it stops receiving any more keyboard or mouse events. Through a low-level system-wide hook the global keyboard / mouse hook is able to deliver those events regardless.

The Java (low-level) System Hook comes bundled with native libraries (for Windows 32 & 64 bit) to register the hooks via the Java Native Interface (JNI). The libraries are load dynamically depending on the version and architecture of your operating system. The libraries to track the keyboard and mouse events can be loaded and used separately.

Using the GlobalKeyboardHook class a GlobalKeyListener or the adapter class GlobalKeyAdapter can be registered to listen to keyPressed and keyReleased events like so:

import java.util.Map.Entry;

import lc.kra.system.keyboard.GlobalKeyboardHook;
import lc.kra.system.keyboard.event.GlobalKeyAdapter;
import lc.kra.system.keyboard.event.GlobalKeyEvent;

public class GlobalKeyboardExample {

    private static boolean run = true;

    public static void main(String[] args) {
        // Might throw a UnsatisfiedLinkError if the native library fails to load or a RuntimeException if hooking fails 
        GlobalKeyboardHook keyboardHook = new GlobalKeyboardHook(true); // Use false here to switch to hook instead of raw input

        System.out.println("Global keyboard hook successfully started, press [escape] key to shutdown. Connected keyboards:");

        for (Entry<Long, String> keyboard : GlobalKeyboardHook.listKeyboards().entrySet()) {
            System.out.format("%d: %s\n", keyboard.getKey(), keyboard.getValue());
        }

        keyboardHook.addKeyListener(new GlobalKeyAdapter() {

            @Override 
            public void keyPressed(GlobalKeyEvent event) {
                System.out.println(event);
                if (event.getVirtualKeyCode() == GlobalKeyEvent.VK_ESCAPE) {
                    run = false;
                }
            }

            @Override 
            public void keyReleased(GlobalKeyEvent event) {
                System.out.println(event); 
            }
        });

        try {
            while(run) { 
                Thread.sleep(128); 
            }
        } catch(InterruptedException e) { 
            //Do nothing
        } finally {
            keyboardHook.shutdownHook(); 
        }
    }
}

Using the GlobalMouseHook class a GlobalMouseListener or the adapter class GlobalMouseAdapter can be registered to listen to mousePressed, mouseReleased, mouseMoved and mouseWheel events like so:

import java.util.Map.Entry;

import lc.kra.system.mouse.GlobalMouseHook;
import lc.kra.system.mouse.event.GlobalMouseAdapter;
import lc.kra.system.mouse.event.GlobalMouseEvent;

public class GlobalMouseExample {

    private static boolean run = true;

    public static void main(String[] args) {
        // Might throw a UnsatisfiedLinkError if the native library fails to load or a RuntimeException if hooking fails 
        GlobalMouseHook mouseHook = new GlobalMouseHook(); // Add true to the constructor, to switch to raw input mode

        System.out.println("Global mouse hook successfully started, press [middle] mouse button to shutdown. Connected mice:");

        for (Entry<Long,String> mouse:GlobalMouseHook.listMice().entrySet()) {
            System.out.format("%d: %s\n", mouse.getKey(), mouse.getValue());
        }

        mouseHook.addMouseListener(new GlobalMouseAdapter() {

            @Override 
            public void mousePressed(GlobalMouseEvent event)  {
                System.out.println(event);
                if ((event.getButtons() & GlobalMouseEvent.BUTTON_LEFT) != GlobalMouseEvent.BUTTON_NO
                && (event.getButtons() & GlobalMouseEvent.BUTTON_RIGHT) != GlobalMouseEvent.BUTTON_NO) {
                    System.out.println("Both mouse buttons are currently pressed!");
                }
                if (event.getButton()==GlobalMouseEvent.BUTTON_MIDDLE) {
                    run = false;
                }
            }

            @Override 
            public void mouseReleased(GlobalMouseEvent event)  {
                System.out.println(event); 
            }

            @Override 
            public void mouseMoved(GlobalMouseEvent event) {
                System.out.println(event); 
            }

            @Override 
            public void mouseWheel(GlobalMouseEvent event) {
                System.out.println(event); 
            }
        });

        try {
            while(run) { 
                Thread.sleep(128); 
            }
        } catch(InterruptedException e) { 
            //Do nothing
        } finally {
            mouseHook.shutdownHook(); 
        }
    }
}

Please find some background information about this framework on my blog.

Usage

Feel free to use the classes lc.kra.system.keyboard.GobalKeyboardHook and lc.kra.system.mouse.GlobalMouseHook by coping the .java files to your project. Alternatively check the releases section for pre-bundled Java archives (JAR).

The LibraryLoader will first attempt to load the native libraries from the java.library.path and fall back checking the archives /lc/kra/system/lib package, if no libraries where found.

Maven Dependency

You can include system-hook as a dependency from Maven Central by adding it to your pom.xml:

<dependency>
  <groupId>lc.kra.system</groupId>
  <artifactId>system-hook</artifactId>
  <version>3.8</version>
</dependency>

Build

To build system-hook on your machine, checkout the repository, cd into it, and call:

mvn clean install

(A C99 compatible compiler / linker bundle is required to build the native libraries, see MSYS2)

License

The code is available under the terms of the MIT License.