🎮 Input4j - The pure Java input library

Input4j is a modern Java input library built on the Foreign Function & Memory API (FFM).
It provides fast, cross-platform controller and gamepad input without requiring JNI or native binaries.

🚀 Features

• 🎮 Game controller input support
• ⚡ Native performance via Java FFM API
• 🧩 No JNI required
• 🖥 Cross-platform (Windows / Linux / macOS)
• 📦 Available on Maven Central
• 🧪 Lightweight and dependency-free

Why input4j?

• Cross-Platform Input handling: Fully compatible with Windows, Linux, and OSX.
• Performance: Optimized for high performance with minimal overhead.
• Flexible Input Handling: Supports both polling and event-based input mechanisms.
• Simplicity: Easy to integrate and use with straightforward APIs.
• Future-Proof: Built on the latest Java technologies, ensuring long-term support and compatibility.

🆚 Advantages over traditional java input libraries

Input4j offers several advantages over traditional libraries like JInput by leveraging the new Foreign Function & Memory API (FFM API) instead of using Java Native Interface (JNI). It is a more modern and efficient JNI alternative and an easy way to interact with native input libraries, providing the following benefits:

• No Native Artifacts & No Dependencies: Direct interaction with native libraries without the need for additional native artifacts simplifies the build and deployment process.
• Performance: Based on the FFM API, this library reduces the overhead associated with native calls, resulting in significantly faster performance then Java JNI.
• Safety: Safer memory management and access patterns reduce the risk of memory leaks and buffer overflows.
• Ease of Use: A more straightforward and modern API makes it easier to write and maintain code.
• Future-Proof: Built on the latest Java technologies, ensuring long-term support and compatibility with future Java versions.

📦️ Installation

Gradle

Add the following dependency to your build.gradle file to start using Input4j:

dependencies {
  implementation 'de.gurkenlabs:input4j:1.0.0'
}

Maven

<dependency>
  <groupId>de.gurkenlabs</groupId>
  <artifactId>input4j</artifactId>
  <version>1.0.0</version>
</dependency>

💻 Quick start guide

Manually Polling and Reading Input Data

try (var inputDevices = InputDevices.init()) {
  while (!inputDevices.getAll().isEmpty()) {
    // iterate all available input devices and poll their data every second
    for (var inputDevice : inputDevices.getAll()) {
      inputDevice.poll();
      System.out.println(inputDevice.getInstanceName() + ":" + inputDevice.getComponents());
    }

    Thread.sleep(1000);
  }
}

Event-Based Input Handling

try (var devices = InputDevices.init()) {
  var device = devices.getAll().stream().findFirst().orElse(null);
  if (device == null) {
    System.out.println("No input devices found.");
    return;
  }

  device.onInputValueChanged(e -> System.out.println("Value changed: " + e.component() + " -> " + e.newValue()));
  device.onButtonPressed(XInput.X, () -> System.out.println("X button pressed"));
  device.onAxisChanged(Axis.AXIS_X, value -> System.out.println("X axis: " + value));

  // simulate external polling loop
  while (true) {
    device.poll();
    Thread.sleep(1000);
  }
}

Used By

input4j is the input system used by the LITIENGINE Java game engine.

🔌 Technical Details

Platform-Specific Input APIs

• Windows: DirectInput ✅

  • Full implementation using dinput.h
  • Supports legacy and modern input devices

• Windows: XInput ✅

  • Modern gamepad support via xinput.h
  • Xbox controller compatibility

• Linux: evdev ✅

  • Event interface via /dev/input

• macOS: IOKit ✅

  • HID device provisioning via IOHIDManager

System Requirements

• Java Runtime: 22+

Linux Permissions

On Linux, Input4j uses the modern evdev API (/dev/input/event*) which provides detailed input information. This is the same approach used by SDL2 and other modern gamepad libraries.

The /dev/input/event* devices are owned by root:input with restricted access (640).

Quick fix - Add user to input group:

sudo usermod -a -G input $USER
# Log out and log back in for changes to take effect

Permanent solution - Create udev rules: Create /etc/udev/rules.d/99-input4j.rules:

SUBSYSTEM=="input", ENV{ID_INPUT_JOYSTICK}=="1", MODE="0666"

Then reload the rules:

sudo udevadm control --reload-rules
# Reconnect your gamepad

Verify your setup:

# Check device permissions
ls -la /dev/input/event*

# Check if user is in input group
getent group input

Note: Input4j uses the modern evdev API (/dev/input/event*) rather than the legacy joystick API (/dev/input/js*). Both require the same permissions, but evdev provides more detailed input information. This is the standard approach used by SDL2 and other modern Linux input libraries.