Two separate browser sessions play the first six moves of a chess game; each move goes through the JSocket server and appears on the other board right away. Click for the full-quality MP4.

JSocket provides a simple WebSocket implementation in Java with no external dependencies. It is useful for learning WebSocket internals, building custom real-time features, or adding WebSocket support to existing Java applications.

• Beginner-friendly code structure with extensive documentation
• RFC 6455 compliant WebSocket implementation
• Concurrent client handling with dedicated reader/writer threads
• Event-driven architecture via simple listener interface
• Working Chess game demo showcasing real-time capabilities
• Zero external dependencies: only the Java standard library

Requires a JDK (8 or newer). From a terminal:

git clone https://github.com/AceAtDev/JSocket--java-simple-websocket
cd JSocket--java-simple-websocket

# Compile everything into out/
javac -d out $(find javaWebsocketChess -name "*.java")

# Start the chess server (default port 8080; pass another port as an argument)
java -cp out javaWebsocketChess.chess.ChessServerMain

Then open javaWebsocketChess/chess/clientApp/index.html in two browser tabs or windows. The first one to connect plays White, the second plays Black. If you started the server on a different port, add it to the page URL, for example index.html?port=8765.

The GIF above was recorded with docs/demo/record_demo.py. It compiles and starts the server, plays six moves in two Playwright browser sessions, and builds the MP4 and GIF with ffmpeg:

pip install playwright && playwright install chromium
python docs/demo/record_demo.py            # or: --port 8765 if 8080 is busy

1️⃣ Copy the core files from javaWebsocketChess/websocketCore/ into your project (the classes use the package javaWebsocketChess.websocketCore.src.main.java.com.jSocket.websocket, so keep that folder layout or update the package and import lines)

2️⃣ Create your handler:

public class MyWebSocketHandler implements WebSocketListener {
    @Override
    public void onOpen(ClientHandler connection) {
        connection.sendMessage("Welcome!");
    }

    @Override
    public void onMessage(ClientHandler connection, String message) {
        System.out.println("Received: " + message);
        connection.sendMessage("You said: " + message);
    }

    @Override
    public void onClose(ClientHandler connection, int code, String reason, boolean remote) {
        System.out.println("Connection closed: " + reason);
    }

    @Override
    public void onError(ClientHandler connection, Exception ex) {
        ex.printStackTrace();
    }
}

3️⃣ Start the server:

public static void main(String[] args) {
    WebSocketServer server = new WebSocketServer(8888, new MyWebSocketHandler());
    try {
        server.start();
        System.out.println("WebSocket server running on port 8888");
    } catch (IOException e) {
        e.printStackTrace();
    }
}

JSocket has five main parts:

• WebSocketServer: Manages TCP connections and handshakes
• ClientHandler: Manages WebSocket connection lifecycle
• WebSocketDataReader/Writer: Handle frame reading/writing
• WebSocketFrame: Represents WebSocket protocol frames
• WebSocketListener: Interface for your application logic

• Learning WebSocket internals without complex dependencies
• Real-time chat applications
• Multiplayer games (like the included Chess demo)
• Live dashboards and monitoring tools
• Adding WebSocket capability to existing Java applications

For more detailed information:

• how it works - Detailed description of classes and methods

Contributions are welcome! Whether it's bug reports, feature requests, or code contributions:

• Fork the repository
• Create your feature branch: git checkout -b feature/amazing-feature
• Commit your changes: git commit -m 'Add some amazing feature'
• Push to the branch: git push origin feature/amazing-feature
• Open a Pull Request

JSocket is MIT licensed.

Report Bug • Request Feature

Special thanks to the amazing python-websockets/websockets project for their wonderful documentation, which was invaluable in creating this repository.