Handling WebSocket Messages and Events in Spring Boot

WebSocket is a communication protocol that provides full-duplex communication channels over a single TCP connection. It enables real-time communication between clients and servers, making it suitable for applications that require instant updates or notifications.

In this article, we will explore how to handle WebSocket messages and events using Spring Boot. We will leverage the power of the "Spring WebSocket" module, which provides an easy-to-use API for WebSocket communication.

Setting up a WebSocket Endpoint

To get started, we need to set up a WebSocket endpoint that handles incoming messages and events. In Spring Boot, we can achieve this by creating a new class and annotating it with the @Controller and @MessageMapping annotations.

@Controller
public class WebSocketController {
  
  @MessageMapping("/hello")
  @SendTo("/topic/greetings")
  public Greeting handleHelloMessage(HelloMessage message) {
    return new Greeting("Hello, " + message.getName() + "!");
  }
  
}

In the above example, we have defined a WebSocket endpoint at the /hello URI. Any message sent to this endpoint will be received by the handleHelloMessage method. The method processes the message and returns a Greeting object, which will be broadcasted to all subscribers of the /topic/greetings channel.

Configuring WebSocket Support in Spring Boot

To enable WebSocket support in our Spring Boot application, we need to create a configuration class annotated with the @Configuration and @EnableWebSocketMessageBroker annotations.

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
  
  @Override
  public void configureMessageBroker(MessageBrokerRegistry registry) {
    registry.enableSimpleBroker("/topic");
    registry.setApplicationDestinationPrefixes("/app");
  }

  @Override
  public void registerStompEndpoints(StompEndpointRegistry registry) {
    registry.addEndpoint("/ws").withSockJS();
  }
  
}

In the above configuration class, we are enabling a simple message broker that broadcasts messages to subscribers on topics prefixed with /topic. We also configure an application destination prefix of /app for our WebSocket endpoints. Finally, we register a WebSocket endpoint at the /ws URI and enable fallback options using the SockJS library.

Using WebSocket on the Client Side

To consume WebSocket messages on the client side, we can use the Stomp.js library, which provides a simple and flexible way to interact with WebSocket-based servers.

var socket = new WebSocket("ws://localhost:8080/ws");
var stompClient = Stomp.over(socket);

stompClient.connect({}, function (frame) {
    console.log('Connected: ' + frame);
    
    stompClient.subscribe('/topic/greetings', function (greeting) {
        console.log('Received message: ' + greeting.body);
    });
});

In the above JavaScript snippet, we establish a WebSocket connection to ws://localhost:8080/ws and create a STOMP client using the Stomp.js library. We then connect to the WebSocket endpoint and subscribe to the /topic/greetings channel to receive greetings from the server.

Conclusion

WebSocket provides a powerful mechanism for real-time communication between clients and servers. In this article, we explored how to handle WebSocket messages and events in a Spring Boot application. We set up a WebSocket endpoint, configured WebSocket support, and consumed WebSocket messages on the client side using the Stomp.js library. With these tools, we can easily build applications that require instant updates and notifications.

To learn more about WebSocket communication in Spring Boot, I recommend checking out the "REST with Spring Boot" course, which covers this topic in detail.

Happy coding!