How to emulate pressing media keys in Java?

Question

How can I emulate pressing media keys in Java? Such as play/pause, next/previous, volume control.

C# has VK_MEDIA_PLAY_PAUSE, VK_MEDIA_NEXT_TRACK

Answer 1

I used the JNI Library to simulate the key presses using code written in C. I've created a .dll file and .java file for hitting the "Volume Down", "Volume Up", "Volume Mute", "Previous Track", "Next Track", and "Play/Pause Track" media keys.

Here is a link to the full repository, however, I will explain it in more detail below.

MediaKeys.java must be in a package named "commands" to work.

MediaKeys.dll must be in same path as the "src" folder or in the same path as the .class file when compiled.

MediaKeys.java file contains the following:

package commands

public class MediaKeys {

    //loads library from "MediaKeys.dll"
    static {
        System.loadLibrary("MediaKeys");
    }



    public static native void volumeMute();

    public static native void volumeDown();

    public static native void volumeUp();


    public static native void songPrevious();

    public static native void songNext();

    public static native void songPlayPause();



    //test driver
    public static void main(String[] args) {

        //volumeMute();

    }

}

The static block loads the .dll file and then the functions programmed in C are declared using the native keyword.

If you only need the functions, then you can use the .dll file for Windows. If you require the source code for the .dll it is included in the link above and I will explain it in more detail below.

The .dll is made from two files, a C file for the functions' source code and a header file. (Named MediaKeys.c and MediaKeys.h)

The MediaKeys.c contains the code that presses the desired keys. In order to preserve space, the following code blocks for the C and header files are formatted only for "Next Track", "Previous Track", and "Pause/Play Track" functions.

The header file: MediaKeys.h

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class MediaKeys */

#ifndef _Included_MediaKeys
#define _Included_MediaKeys
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     MediaKeys
 * Method:    songPrevious
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_commands_MediaKeys_songPrevious
  (JNIEnv *, jclass);

/*
 * Class:     MediaKeys
 * Method:    songNext
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_commands_MediaKeys_songNext
  (JNIEnv *, jclass);

/*
 * Class:     MediaKeys
 * Method:    songPlayPause
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_commands_MediaKeys_songPlayPause
  (JNIEnv *, jclass);

#ifdef __cplusplus
}
#endif
#endif

The header file contains a statement for each method needed in the following format:

JNIEXPORT void JNICALL Java_{package_name}_{class_name}_{method_name}
  (JNIEnv *, jclass);

The C file must then correspond to the header file. MediaKeys.c

//standard dependencies for C and the JNI Library
#include <jni.h>
#include <stdio.h>
#include "MediaKeys.h"

//dependencies required to hit the media keys
#define WINVER 0x0500
#include <windows.h>


//hits the previous track key
JNIEXPORT void JNICALL Java_commands_MediaKeys_songPrevious (JNIEnv *env, jobject thisObj) {

    KEYBDINPUT kbi;

    //specific keycode
    kbi.wVk = VK_MEDIA_PREV_TRACK; //this can be changed depending on the key

    kbi.wScan = 0;
    kbi.dwFlags = 0;
    kbi.time = 0;
    kbi.dwExtraInfo = (ULONG_PTR) GetMessageExtraInfo();

    INPUT input;
    input.type = INPUT_KEYBOARD;
    input.ki   = kbi;

    SendInput(1, &input, sizeof(INPUT));

    return;

}


//hits the next track key
JNIEXPORT void JNICALL Java_commands_MediaKeys_songNext (JNIEnv *env, jobject thisObj) {

    KEYBDINPUT kbi;

    //specific keycode
    kbi.wVk = VK_MEDIA_NEXT_TRACK;

    kbi.wScan = 0;
    kbi.dwFlags = 0;
    kbi.time = 0;
    kbi.dwExtraInfo = (ULONG_PTR) GetMessageExtraInfo();

    INPUT input;
    input.type = INPUT_KEYBOARD;
    input.ki   = kbi;

    SendInput(1, &input, sizeof(INPUT));

    return;

}


//hits the play/pause key
JNIEXPORT void JNICALL Java_commands_MediaKeys_songPlayPause (JNIEnv *env, jobject thisObj) {

    KEYBDINPUT kbi;

    //specific keycode
    kbi.wVk = VK_MEDIA_PLAY_PAUSE;

    kbi.wScan = 0;
    kbi.dwFlags = 0;
    kbi.time = 0;
    kbi.dwExtraInfo = (ULONG_PTR) GetMessageExtraInfo();

    INPUT input;
    input.type = INPUT_KEYBOARD;
    input.ki   = kbi;

    SendInput(1, &input, sizeof(INPUT));

    return;

}

The C file contains a corresponding function for each header statement following the format below:

JNIEXPORT void JNICALL Java_{package_name}_{class_name}_{method_name} (JNIEnv *env, jobject thisObj) {

    //specific code goes here
    return;

}

And as noted in the code, you can change the specific key by changing: kbi.wVk = specific_key_goes_here;. A list of available keys can be found here.

Once the C and header files are created, they can then be compiled into a dll file. To do this, I used Code::Blocks to create a new Dynamic Link Library project, added the MediaKeys.c and MediaKeys.h files, and clicked build.

Since my JVM is 64-bit and Code::Blocks default compiler is 32-bit, I had to install a 64-bit compiler into Code::Blocks.

You also must add links to the jni.h libraries. To do this in Code::Blocks go to Settings>Compiler>Search Directories and add the directories C:\Program Files\Java\jdk1.8.0_171\include and C:\Program Files\Java\jdk1.8.0_171\include\win32. You will most likely have to change the file paths depending on your jdk version.

Once built, then copy the dll file to the required location for the java program.

For more information about setting up the Java Native Interface, I found this link exceptionally helpful.

I know this post is a bit old but I figured this information might help others.

Answer 2

You can achieve it with https://github.com/kwhat/jnativehook and afterwards spy on the keys. In my question I've written some sample methods:

public static void MediaKeyForward(){
    GlobalScreen.postNativeEvent(new NativeKeyEvent(2401,0,176,57369,org.jnativehook.keyboard.NativeKeyEvent.CHAR_UNDEFINED));

}
public static void MediaKeyBack(){
    GlobalScreen.postNativeEvent(new NativeKeyEvent(2401,0,177,57360,org.jnativehook.keyboard.NativeKeyEvent.CHAR_UNDEFINED));

}
public static void MediaKeyPause(){
 GlobalScreen.postNativeEvent(new NativeKeyEvent(2401,0,179,57378,org.jnativehook.keyboard.NativeKeyEvent.CHAR_UNDEFINED));

}

Everything to do is to include the library into your project. A sample of how to spy on keys and get the neccesary Parameters to create a key event can be found here.

Answer 3

Create your own keylistener and spy for whatever comes and then use this value. Here is simple KeySpy class:

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JLabel;


public class KeySpy {
    JLabel label=new JLabel("Enter the key");
    public KeySpy() {
        JFrame frame=new JFrame("KeySpy");
        frame.add(label);

        frame.addKeyListener(new KeyListener() {

            @Override
            public void keyTyped(KeyEvent e) {
            }

            @Override
            public void keyReleased(KeyEvent e) {
            }

            @Override
            public void keyPressed(KeyEvent e) {
                label.setText(e.toString());
                System.out.println(e.toString());
            }
        });

        frame.setSize(200, 200);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        new KeySpy();

    }

}

and here is result for 2 buttons on my keyboard

   [Stop] = java.awt.event.KeyEvent[KEY_PRESSED,keyCode=0,keyText=Unknown keyCode: 0x0,keyChar=Undefined keyChar,keyLocation=KEY_LOCATION_STANDARD,rawCode=178,primaryLevelUnicode=0,scancode=36,extendedKeyCode=0x0] on frame0

   [Mute] = java.awt.event.KeyEvent[KEY_PRESSED,keyCode=0,keyText=Unknown keyCode: 0x0,keyChar=Undefined keyChar,keyLocation=KEY_LOCATION_STANDARD,rawCode=173,primaryLevelUnicode=0,scancode=32,extendedKeyCode=0x0] on frame0

As you can see they do not have keyCode but they do have rawCode - so use it.

Answer 4

I improved Alex's KeySpy application. The JFrame holds the focus so you can minimize or maximize the application, and still press any key when the application is in focus.

Here's the GUI.

I put the information in a label / value grid to make it easier to find the value(s) that you're interested in.

And here's the code. This is a good example of a GridBagLayout.

package com.ggl.testing;

import java.awt.Component;
import java.awt.Container;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class KeySpy implements Runnable {

    private KeySpyPanel keySpyPanel;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new KeySpy());
    }

    @Override
    public void run() {
        final JFrame frame = new JFrame("Key Spy");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationByPlatform(true);
        frame.addWindowFocusListener(new WindowAdapter() {
            public void windowGainedFocus(WindowEvent e) {
                frame.requestFocusInWindow();
            }
        });

        keySpyPanel = new KeySpyPanel();
        frame.add(keySpyPanel.getPanel());
        frame.addKeyListener(new KeyPressedListener(this));

        frame.pack();
        frame.setVisible(true);
    }

    public KeySpyPanel getKeySpyPanel() {
        return keySpyPanel;
    }

    public class KeySpyPanel {

        private final Insets bottomInsets = new Insets(10, 10, 10, 10);
        private final Insets normalInsets = new Insets(10, 10, 0, 10);

        private JPanel panel;

        private JTextField keyCodeField;
        private JTextField keyTextField;
        private JTextField keyCharField;
        private JTextField keyLocationField;
        private JTextField modifiersField;
        private JTextField extModifiersField;
        private JTextField rawCodeField;
        private JTextField primaryLevelUnicodeField;
        private JTextField scancodeField;
        private JTextField extendedKeyCodeField;

        public KeySpyPanel() {
            createPartControl();
        }

        private void createPartControl() {
            panel = new JPanel();
            panel.setLayout(new GridBagLayout());

            int gridy = 0;

            JLabel anyKeyLabel = new JLabel("Press any key");
            anyKeyLabel.setFont(anyKeyLabel.getFont().deriveFont(36F));
            anyKeyLabel.setHorizontalAlignment(JLabel.CENTER);
            addComponent(panel, anyKeyLabel, 0, gridy++, 2, 1, normalInsets,
                    GridBagConstraints.CENTER, GridBagConstraints.HORIZONTAL);

            JLabel keyCodeLabel = new JLabel("KeyCode:");
            addComponent(panel, keyCodeLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            keyCodeField = new JTextField(20);
            keyCodeField.setEditable(false);
            addComponent(panel, keyCodeField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel keyTextLabel = new JLabel("KeyText:");
            addComponent(panel, keyTextLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            keyTextField = new JTextField(20);
            keyTextField.setEditable(false);
            addComponent(panel, keyTextField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel keyCharLabel = new JLabel("KeyChar:");
            addComponent(panel, keyCharLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            keyCharField = new JTextField(20);
            keyCharField.setEditable(false);
            addComponent(panel, keyCharField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel keyLocationLabel = new JLabel("KeyLocation:");
            addComponent(panel, keyLocationLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            keyLocationField = new JTextField(20);
            keyLocationField.setEditable(false);
            addComponent(panel, keyLocationField, 1, gridy++, 1, 1,
                    normalInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel modifiersLabel = new JLabel("Modifiers:");
            addComponent(panel, modifiersLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            modifiersField = new JTextField(20);
            modifiersField.setEditable(false);
            addComponent(panel, modifiersField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel extModifiersLabel = new JLabel("ExtModifiers:");
            addComponent(panel, extModifiersLabel, 0, gridy, 1, 1,
                    normalInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            extModifiersField = new JTextField(20);
            extModifiersField.setEditable(false);
            addComponent(panel, extModifiersField, 1, gridy++, 1, 1,
                    normalInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel rawCodeLabel = new JLabel("RawCode:");
            addComponent(panel, rawCodeLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            rawCodeField = new JTextField(20);
            rawCodeField.setEditable(false);
            addComponent(panel, rawCodeField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel primaryLevelUnicodeLabel = new JLabel("PrimaryLevelUnicode:");
            addComponent(panel, primaryLevelUnicodeLabel, 0, gridy, 1, 1,
                    normalInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            primaryLevelUnicodeField = new JTextField(20);
            primaryLevelUnicodeField.setEditable(false);
            addComponent(panel, primaryLevelUnicodeField, 1, gridy++, 1, 1,
                    normalInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel scancodeLabel = new JLabel("Scancode:");
            addComponent(panel, scancodeLabel, 0, gridy, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            scancodeField = new JTextField(20);
            scancodeField.setEditable(false);
            addComponent(panel, scancodeField, 1, gridy++, 1, 1, normalInsets,
                    GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            JLabel extendedKeyCodeLabel = new JLabel("ExtendedKeyCode:");
            addComponent(panel, extendedKeyCodeLabel, 0, gridy, 1, 1,
                    bottomInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);

            extendedKeyCodeField = new JTextField(20);
            extendedKeyCodeField.setEditable(false);
            addComponent(panel, extendedKeyCodeField, 1, gridy++, 1, 1,
                    bottomInsets, GridBagConstraints.LINE_START,
                    GridBagConstraints.HORIZONTAL);
        }

        private void addComponent(Container container, Component component,
                int gridx, int gridy, int gridwidth, int gridheight,
                Insets insets, int anchor, int fill) {
            GridBagConstraints gbc = new GridBagConstraints(gridx, gridy,
                    gridwidth, gridheight, 1.0D, 1.0D, anchor, fill, insets, 0,
                    0);
            container.add(component, gbc);
        }

        public JPanel getPanel() {
            return panel;
        }

        public void setKeyPressed(KeyEvent event) {
            String s = event.toString();

            keyCodeField.setText(getValue("keyCode", s));
            keyTextField.setText(getValue("keyText", s));
            keyCharField.setText(getValue("keyChar", s));
            keyLocationField.setText(getValue("keyLocation", s));
            modifiersField.setText(getValue("modifiers", s));
            extModifiersField.setText(getValue("extModifiers", s));
            rawCodeField.setText(getValue("rawCode", s));
            primaryLevelUnicodeField
                    .setText(getValue("primaryLevelUnicode", s));
            scancodeField.setText(getValue("scancode", s));
            extendedKeyCodeField.setText(getValue("extendedKeyCode", s));
        }

        private String getValue(String key, String line) {
            int sPos = line.indexOf(key);
            if (sPos >= 0) {
                int nPos = sPos + key.length() + 1;
                int ePos = line.indexOf(",", nPos);
                if (ePos < 0) {
                    ePos = line.indexOf("]", nPos);
                }
                if (ePos >= 0) {
                    return line.substring(nPos, ePos);
                }
            }

            return "";
        }

    }

    public class KeyPressedListener extends KeyAdapter {

        private KeySpy keySpyFrame;

        public KeyPressedListener(KeySpy keySpyFrame) {
            this.keySpyFrame = keySpyFrame;
        }

        @Override
        public void keyPressed(KeyEvent event) {
            keySpyFrame.getKeySpyPanel().setKeyPressed(event);
        }
    }

}