The WebSocket protocol allows you to implement bidirectional communication between applications. It is important to know that HTTP is used only for the initial handshake. After it happens, the HTTP connection is upgraded to a newly opened TCP/IP connection that is used by a WebSocket.
The WebSocket protocol is a rather low-level protocol. It defines how a stream of bytes is transformed into frames. A frame may contain a text or a binary message. Because the message itself does not provide any additional information on how to route or process it, It is difficult to implement more complex applications without writing additional code. Fortunately, the WebSocket specification allows using of sub-protocols that operate on a higher, application level. One of them, supported by the Spring Framework, is STOMP.
STOMP is a simple text-based messaging protocol that was initially created for scripting languages such as Ruby, Python, and Perl to connect to enterprise message brokers. Thanks to STOMP, clients and brokers developed in different languages can send and receive messages to and from each other. The WebSocket protocol is sometimes called TCP for Web. Analogically, STOMP is called HTTP for Web. It defines a handful of frame types that are mapped onto WebSockets frames, e.g., CONNECT, SUBSCRIBE, UNSUBSCRIBE, ACK, or SEND. On one hand, these commands are very handy to manage communication while, on the other, they allow us to implement solutions with more sophisticated features like message acknowledgment.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-websocket</artifactId>
</dependency>
additional libs for js:
<dependency>
<groupId>org.webjars</groupId>
<artifactId>webjars-locator-core</artifactId>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>sockjs-client</artifactId>
<version>1.0.2</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>stomp-websocket</artifactId>
<version>2.3.3</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>bootstrap</artifactId>
<version>3.3.7</version>
</dependency>
<dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.1.1-1</version>
</dependency>
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
@Override
public void registerStompEndpoints(StompEndpointRegistry registry) {
registry.addEndpoint("/gs-guide-websocket").withSockJS();
}
@Override
public void configureMessageBroker(MessageBrokerRegistry registry) {
registry.enableSimpleBroker("/topic");
registry.setApplicationDestinationPrefixes("/app");
}
}
- "/gs-guide-websocket" - main registration point WebSocket (means 'connection')
registry.enableSimpleBroker("/topic");- set prefix for all topics (Ex.: '/topic/ahah', '/topic/dog')registry.setApplicationDestinationPrefixes("/app");- set prefix for send message interaction (Ex.: '/api/books')
@Controller
public class GreetingController {
@MessageMapping("/hello")
@SendTo("/topic/greetings")
public Greeting greeting(HelloMessage message) throws Exception {
Thread.sleep(1000); // simulated delay
return new Greeting("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!");
}
}
@MessageMapping("/hello")- handle message send to route: '/api/hello' (remember prefix!)@SendTo("/topic/greetings")- send to everyone who is subscribed to this topic
- Click to connect to WebSocket route: '/gs-guide-websocket'
- After connect to WebSocket auto subscribe to topic: '/topic/greetings' (it means to receive all messages that were sent to this topic)
- Click "send" (send name) to route: '/app/hello' and return greeting message
/test/java/com/example/messagingstompwebsocket/WebSocketClientTest.java