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Read: Class 19 Read: 19 - Spring and Sockets

Real time messaging with websockets

  1. STOMP is a subprotocol operating on top of the lower-level WebSocket.

Using WebSocket to build an interactive web application

  1. generate a new project with the required dependency (Websocket).
    • implementation 'org.webjars:webjars-locator-core'
    • implementation 'org.webjars:sockjs-client:1.0.2'
    • implementation 'org.webjars:stomp-websocket:2.3.3'
    • implementation 'org.webjars:bootstrap:3.3.7'
    • implementation 'org.webjars:jquery:3.1.1-1'
  2. model the message that carries the name, create a plain old Java object with a name property and a corresponding getName()
  3. model the greeting representation, add another plain old Java object with a content property and a corresponding getContent() method

Create a Message-handling Controller

  1. The @MessageMapping annotation ensures that, if a message is sent to the /hello destination, the greeting() method is called.
  2. After the one-second delay, the greeting() method creates a Greeting object and returns it.
  3. The return value is broadcast to all subscribers of /topic/greetings, as specified in the @SendTo annotation.

Configure Spring for STOMP messaging

  1. Create a Java class named WebSocketConfig

    •   @Configuration
  @EnableWebSocketMessageBroker
  public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
  @Override
  public void configureMessageBroker(MessageBrokerRegistry config) {
      config.enableSimpleBroker("/topic");
      config.setApplicationDestinationPrefixes("/app");
  }
  @Override
  public void registerStompEndpoints(StompEndpointRegistry registry) {
      registry.addEndpoint("/gs-guide-websocket").withSockJS();
  }
  }

  2. @Configuration to indicate that it is a Spring configuration class.

  3. @EnableWebSocketMessageBroker enables WebSocket message handling, backed by a message broker.

  4. enableSimpleBroker() to:

    • enable a simple memory-based message broker to carry the greeting messages back to the client on destinations prefixed with /topic
    • designates the /app prefix for messages that are bound for methods annotated with @MessageMapping

  5. The registerStompEndpoints() method registers the /gs-guide-websocket endpoint,

    • enabling SockJS fallback options so that alternate transports can be used if WebSocket is not available.
    • The SockJS client will attempt to connect to /gs-guide-websocket and use the best available transport (websocket, xhr-streaming, xhr-polling, and so on).

Create a Browser Client

  1. This HTML file imports the SockJS and STOMP javascript libraries that will be used to communicate with our server through STOMP over websocket.