Spring's WebSocket implementation provides an abstraction layer on top of other WebSocket runtimes, such as Tomcat, Jetty, and Undertow. With Spring's abstraction, creating a WebSocket server is as simple as implementing the WebSocketHandler interface. Spring also provides base classes, such as TextWebSocketHandler and BinaryWebSocketHandler, that we can extend directly.

Besides implementing WebSocketHandler, we will also need to provide the configuration so that Spring knows how to bootstrap our WebSocket server. We can do this by implementing the WebSocketConfigurer interface. Here is an example of how a simple WebSocket configuration looks:

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(realTimeHandler(), "/ws");
  }

  @Bean
  public WebSocketHandler realTimeHandler() {
    return new RealTimeHandler();
  }
}

As you can see, we apply the @EnableWebSocket annotation to the configuration class and in the registerWebSocketHandlers() method, we register realTimeHander to the /ws path. In this way, requests sent to the /ws path will be handled by the RealTimeHandler class.