Broadcasting Messages to Multiple Clients

In today's world of real-time applications, broadcasting messages to multiple clients is a common requirement. In this article, we will discuss how to achieve this using Spring Boot, a popular framework for building Java applications.

Prerequisites

Before we begin, make sure you have the following installed on your system:

• Java Development Kit (JDK)
• Spring Boot
• IDE of your choice (e.g., Eclipse, IntelliJ IDEA)

Setting up the Project

Let's start by creating a new Spring Boot project. You can use Spring Initializr (https://start.spring.io/) or your preferred method to generate the project structure with the necessary dependencies.

Once you have the project structure ready, open it in your IDE and let's move on to the next step.

Creating a WebSocket Endpoint

To enable real-time communication between clients and the server, we will use WebSocket. Create a new Java class called WebSocketEndpoint and annotate it with @ServerEndpoint as shown below:

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint("/broadcast")
public class WebSocketEndpoint {
    // TODO: Implement endpoint logic
}

The @ServerEndpoint annotation tells Spring Boot that this class will handle WebSocket connections at the specified endpoint ("/broadcast").

Broadcasting Messages

Inside the WebSocketEndpoint class, we need to implement the logic for broadcasting messages. We can keep track of connected clients using a Set data structure. Here's an example implementation:

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

@ServerEndpoint("/broadcast")
public class WebSocketEndpoint {
    private static final Set<Session> sessions = Collections.synchronizedSet(new HashSet<>());

    @OnOpen
    public void onOpen(Session session) {
        sessions.add(session);
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        // Broadcast the message to all connected clients
        for (Session s : sessions) {
            try {
                s.getBasicRemote().sendText(message);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    @OnClose
    public void onClose(Session session) {
        sessions.remove(session);
    }
}

In the onOpen method, we add the new session to our sessions set. The onMessage method is triggered whenever a client sends a message. Inside this method, we iterate over all the sessions and use the getBasicRemote().sendText() method to send the message to each client. Finally, in the onClose method, we remove the closed session from the set.

Testing the Application

To test our application, build and run the Spring Boot project. You can use a WebSocket client tool like wscat or any WebSocket-enabled frontend application.

Connect multiple clients to the WebSocket endpoint "ws://localhost:8080/broadcast". You should be able to send messages from any client and see them being broadcasted to all connected clients in real-time.

Conclusion

In this article, we learned how to broadcast messages to multiple clients using Spring Boot and WebSocket. By implementing a WebSocket endpoint and keeping track of connected sessions, we were able to achieve real-time communication between the server and clients.

This functionality can be expanded by adding authentication, authorization, and handling various events through WebSocket listeners. WebSocket provides a great foundation for building powerful real-time applications with ease.

Remember to explore the official Spring Boot documentation and experiment with different features to enhance your WebSocket-based application further.