How do you implement a WebSocket controller in Spring Boot?

Table of Contents

• Introduction
• Steps to Implement a WebSocket Controller in Spring Boot
  • 1. Add Dependencies to pom.xml (Maven)
  • 2. Create WebSocket Configuration
    • Example: WebSocket Configuration
  • 3. Create a WebSocket Controller
    • Example: WebSocket Controller
  • 4. Create a WebSocket Client (HTML + JavaScript)
    • Example: WebSocket Client
  • 5. Running the Application
• Conclusion

Introduction

In a Spring Boot application, a WebSocket controller handles real-time communication between the client and the server. WebSockets are particularly useful for applications like chat systems, notifications, and live data feeds where you need bidirectional, low-latency communication. By using Spring’s messaging module with the STOMP protocol over WebSocket, you can easily set up real-time messaging. This guide walks you through implementing a WebSocket controller in Spring Boot.

Steps to Implement a WebSocket Controller in Spring Boot

1. Add Dependencies to pom.xml (Maven)

To begin, you need to include the necessary dependencies in your pom.xml file. These dependencies will provide WebSocket and messaging support in your Spring Boot application.

If you are using Gradle, you can include these dependencies as follows:

These dependencies enable WebSocket communication and message handling using STOMP.

2. Create WebSocket Configuration

Before implementing a WebSocket controller, you need to configure WebSocket support in your Spring Boot application. You can do this by creating a configuration class that registers the WebSocket endpoint and enables messaging.

Example: WebSocket Configuration

In this configuration:

• **@EnableWebSocketMessageBroker**: Enables WebSocket messaging support.
• **configureMessageBroker**: Configures an in-memory message broker with the destination /topic for client subscriptions and /app for messages sent from the client.
• **registerStompEndpoints**: Registers the WebSocket endpoint /ws where clients can connect. It also uses SockJS as a fallback for browsers that do not support WebSocket natively.

3. Create a WebSocket Controller

Now that WebSocket is configured, you can create a controller to handle the messaging logic. The controller will listen for incoming messages, process them, and send responses to subscribed clients.

Example: WebSocket Controller

In this WebSocket controller:

• **@MessageMapping("/hello")**: This annotation maps incoming messages sent to the /app/hello destination to the greeting() method.
• **SimpMessagingTemplate**: This template allows you to send messages to specific destinations. In this case, it sends a message to the /topic/greetings topic, which clients can subscribe to.

4. Create a WebSocket Client (HTML + JavaScript)

To test the WebSocket communication, you can create a simple HTML page with JavaScript to connect to the WebSocket server. The client will send a message to the server and subscribe to a topic to receive responses.

Example: WebSocket Client

In this client:

• **SockJS** provides WebSocket support with fallback for clients that do not support WebSockets natively.
• **STOMP** is used to send messages to the server and subscribe to messages from the server. When the user enters a name and clicks the "Send" button, the client sends the name to the /app/hello destination.
• The client subscribes to the /topic/greetings destination to receive a greeting message from the server.

5. Running the Application

1. Start the Spring Boot application: Run the Spring Boot application using mvn spring-boot:run (for Maven) or gradle bootRun (for Gradle).
2. Open the HTML file: Open the HTML client in a web browser. Ensure that your browser supports WebSockets, or use SockJS as a fallback.
3. Test the WebSocket connection: Enter a name in the input field and click "Send". You should see a greeting message displayed in real-time as the server responds with a message.

Conclusion

Implementing a WebSocket controller in Spring Boot is an effective way to enable real-time communication in your applications. By configuring WebSocket endpoints, handling message mappings with @MessageMapping, and using SimpMessagingTemplate to send messages, you can easily manage bidirectional communication. This setup is ideal for use cases like chat systems, live notifications, and data streaming, making it a powerful tool for modern web applications.