WebSockets with Spring Boot WebFlux: Real-Time Communication

In this post Learn how to build real-time, bi-directional communication channels using WebSockets in Spring Boot with WebFlux.

📑 Table of Contents:

What Are WebSockets?
WebSockets vs SSE vs HTTP
Why Use WebSockets in WebFlux?
Adding WebSocket Support in Spring WebFlux
Creating a WebSocket Handler
Registering WebSocket Routes
Building a WebSocket Client (JavaScript)
Broadcasting Messages (Optional)
Production Considerations
Final Thoughts

🔄 1. What Are WebSockets?

WebSockets provide a full-duplex communication channel over a single TCP connection. This allows the server and client to exchange messages at any time, without re-establishing a connection.

⚔️ 2. WebSockets vs SSE vs HTTP

Feature	HTTP	SSE	WebSockets
Protocol	HTTP/1.1	HTTP/1.1	Custom over TCP
Direction	Request/Response	Server → Client	Bi-directional
Latency	High	Medium	Very low
Use Cases	APIs, Forms	Notifications	Chat, Games, Live Data

⚡ 3. Why Use WebSockets in WebFlux?

Spring WebFlux handles WebSockets natively, providing a non-blocking and reactive pipeline using WebSocketHandler and Reactor Flux/Mono.

Benefits:

Non-blocking messaging
Bi-directional streaming
High scalability for real-time apps

🧱 4. Adding WebSocket Support in Spring WebFlux

WebFlux has built-in support, no extra dependencies needed if using:

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-webflux</artifactId>

</dependency>

👨‍💻 5. Creating a WebSocket Handler

package com.kscodes.springboot.reactive.websocket;

import org.springframework.web.reactive.socket.WebSocketHandler;

import org.springframework.web.reactive.socket.WebSocketSession;

import org.springframework.stereotype.Component;

import reactor.core.publisher.Mono;

@Component

public class EchoWebSocketHandler implements WebSocketHandler {

@Override

public Mono<Void> handle(WebSocketSession session) {

return session.send(

session.receive()

.map(msg -> "Echo: " + msg.getPayloadAsText())

.map(session::textMessage)

);

}

💡 This handler reads incoming messages and sends back an echo response.

🧭 6. Registering WebSocket Routes

package com.kscodes.springboot.reactive.websocket;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import org.springframework.web.reactive.HandlerMapping;

import org.springframework.web.reactive.handler.SimpleUrlHandlerMapping;

import java.util.Map;

@Configuration

public class WebSocketConfig {

@Bean

public HandlerMapping handlerMapping(EchoWebSocketHandler handler) {

return new SimpleUrlHandlerMapping(Map.of("/ws/echo", handler), 1);

}

🌐 7. Building a WebSocket Client (JavaScript)

< script>

const socket = new WebSocket("ws://localhost:8080/ws/echo");

socket.onopen = () => socket.send("Hello WebSocket!");

socket.onmessage = (event) => {

console.log("Received:", event.data);

};

< /script>

✅ This connects to /ws/echo and displays the echoed response.

📢 8. Broadcasting Messages (Optional)

For multi-client broadcast, use a shared FluxProcessor:

Sinks.Many<String> sink = Sinks.many().multicast().onBackpressureBuffer();

Flux<String> messageStream = sink.asFlux();

sink.tryEmitNext("New message");

Use messageStream in your WebSocketHandler to push data to all clients.

🛠️ 9. Production Considerations

Security: Use wss:// over TLS in production
Scalability: Use Redis or Kafka to broadcast across clustered instances
Timeouts: Configure proxy and server timeout settings for long-lived connections
Monitoring: Keep track of active sessions and dropped connections

✅ 10. Final Thoughts

WebSockets in Spring Boot WebFlux make real-time, reactive applications easy to build and scale. With just a few lines of code, you can support chat apps, dashboards, game updates, and more.