Java WebSocket Library: Java-WebSocket

WebSocket in Java: Java-WebSocket Library

In modern web development, the need for real-time two-way communication is becoming increasingly relevant. Chat applications, online games, stock quotes, notifications — all of these require instant data transfer between client and server. For Java, one of the most popular and reliable implementations of the WebSocket protocol is the Java-WebSocket library (also known as nv-websocket-client).

In this article, we will take a detailed look at how to use Java-WebSocket to create server and client applications, provide code examples, and discuss best practices.

What is Java-WebSocket?

Java-WebSocket is a lightweight, powerful open-source library that implements the WebSocket protocol (RFC 6455). It allows Java developers to easily create both WebSocket servers and WebSocket clients without having to delve into the low-level details of the protocol.

Key features of the library:

Full support for both server-side and client-side WebSocket.
Support for WSS (WebSocket Secure) via SSL/TLS.
Automatic reconnection upon connection loss.
Handling of fragmented messages.
Support for custom extensions.
Simple event-based API (onOpen, onMessage, onClose, onError).

Installation and Setup

To use the library, add the dependency to your pom.xml (Maven):

<dependency>    <groupId>org.java-websocket</groupId>    <artifactId>Java-WebSocket</artifactId>    <version>1.5.4</version></dependency>

If you are using Gradle:

implementation 'org.java-websocket:Java-WebSocket:1.5.4'

Creating a WebSocket Server

Let's look at a simple example of a WebSocket server that receives messages and sends them back to all connected clients (echo server):

import org.java_websocket.WebSocket;import org.java_websocket.handshake.ClientHandshake;import org.java_websocket.server.WebSocketServer;import java.net.InetSocketAddress;import java.util.Set;

public class EchoServer extends WebSocketServer {

    public EchoServer(int port) {        super(new InetSocketAddress(port));    }

    @Override    public void onOpen(WebSocket conn, ClientHandshake handshake) {        System.out.println("New connection: " + conn.getRemoteSocketAddress());    }

    @Override    public void onClose(WebSocket conn, int code, String reason, boolean remote) {        System.out.println("Disconnection: " + conn.getRemoteSocketAddress() + " (" + reason + ")");    }

    @Override    public void onMessage(WebSocket conn, String message) {        System.out.println("Received message: " + message);        // Send the message back to all clients        Set<WebSocket> connections = getConnections();        for (WebSocket client : connections) {            client.send("Echo: " + message);        }    }

    @Override    public void onError(WebSocket conn, Exception ex) {        System.err.println("Error: " + ex.getMessage());        if (conn != null) {            conn.close();        }    }

    @Override    public void onStart() {        System.out.println("Server started on port " + getPort());    }

    public static void main(String[] args) {        int port = 8887;        EchoServer server = new EchoServer(port);        server.start();    }}

This server runs on port 8887 and, upon receiving any message, sends it back to all connected clients with the prefix "Echo:".