Spring Websocket Server

To include a WebSocket endpoint to our Spring Boot application, first you need to include the starter package:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-websocket</artifactId>
</dependency>

To configure WebSocket server, we need to define a configuration:

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/websocket")
                .addInterceptors(new HandshakeInterceptor())
                .setAllowedOrigins("*")
                .withSockJS();
    }

    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/channel");
    }

    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.interceptors(new ChannelInterceptor());
    }
}

registerStompEndpoints() is the method to register endpoints for our WebSocket server, in which the first HTTP handshake happens. Here we can use a HanshakeInterceptor() to insert some custom attributes for using when first WebSocket interaction initializes, for example the WebSocket endpoint path.

configureMessageBroker() is used to add channel paths, so our WebSocket clients can subscribe to.

configureClientInboundChannel() is where WebSocket connection make first CONNECT request, then SUBSCRIBE to a channel, etc. ChannelInterceptor() is the place for authorization & authentication our users before sending and receiving messages. In here we can get the attributes we’ve set before in HandshakeInterceptor() instance. Bear in mind that because we do auth in first CONNECT request of WebSocket connection, we have to make the WebSocket endpoints whitelisted in any auth required matchers (Spring Security matchers for instance).

Believe or not, that is all we need to setup a WebSocket server, you now can setup a WebSocket handler and enjoy the magic of Spring.