Spring实战（第四版） 第十八章 使用WebSocket和STOMP实现消息功能

1、使用Spring的低层级WebSocket API

WebSocket通信可以应用于任何类型的应用中，但是WebSocket最常见的应用场景是实现服务器和基于浏览器的应用之间的通信。浏览器中的JavaScript客户端开启一个到服务端的连接，服务器通过这个连接发送更新给浏览器。

public class MarcoHandler extends AbstractWebSocketHandler {

	private static final Logger logger = LoggerFactory.getLogger(MarcoHandler.class);
	
	@Override
	protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
		logger.info("Received message: " + message.getPayload());
		Thread.sleep(2000);
		session.sendMessage(new TextMessage("Polo!"));
	}
	
}

AbstractWebSocketHandler 定义三个方法

• handleBinaryMessage
• handlePongMessage
• handleTextMessage

也可通过afterConnectionEstablished afterConnectionClosed在连接建立、关闭后展开一些操作

注册处理器

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

	@Override
	public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
		registry.addHandler(marcoHandler(), "/marco").withSockJS();
	}
  
	@Bean
	public MarcoHandler marcoHandler() {
		return new MarcoHandler();
	}

}

3、使用STOMP消息

STOMP在WebSocket之上提供了一个基于帧的线路格式层，用来定义消息的语义

启用STOMP消息

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketStompConfig extends AbstractWebSocketMessageBrokerConfigurer {

  @Override
  public void registerStompEndpoints(StompEndpointRegistry registry) {
    registry.addEndpoint("/marcopolo").withSockJS();
  }

  @Override
  public void configureMessageBroker(MessageBrokerRegistry registry) {
//    registry.enableStompBrokerRelay("/queue", "/topic");
    registry.enableSimpleBroker("/queue", "/topic");
    registry.setApplicationDestinationPrefixes("/app");
  }
  
}

处理客户端STOMP消息

使用@MessageMapping注解
Spring也有转换STOMP消息的转换器

@Controller
public class MarcoController {

  private static final Logger logger = LoggerFactory
      .getLogger(MarcoController.class);

  @MessageMapping("/marco")
  public Shout handleShout(Shout incoming) {
    logger.info("Received message: " + incoming.getMessage());

    try { Thread.sleep(2000); } catch (InterruptedException e) {}
    
    Shout outgoing = new Shout();
    outgoing.setMessage("Polo!");
    
    return outgoing;
  }

}

发送消息到客户端

@MessageMapping("/marco")
@SendTo("/topic/shout")
public Shout handleShout(Shout incoming) {
  logger.info("");
  Shout outgoing = new Shout();
  outgoing.setMessage("Polo");
  return outgoing;
}

SimpMessagingTemplate能够在应用的任意地方发送消息

@Service
public class SpittleFeedServiceImpl implements SpittleFeedService {

	private SimpMessagingTemplate messaging;
	private Pattern pattern = Pattern.compile("\\@(\\S+)");
	
	@Autowired
	public SpittleFeedServiceImpl(SimpMessagingTemplate messaging) {
		this.messaging = messaging;
	}
	
	public void broadcastSpittle(Spittle spittle) {
		messaging.convertAndSend("/topic/spittlefeed", spittle);
		
		Matcher matcher = pattern.matcher(spittle.getMessage());
		if (matcher.find()) {
			String username = matcher.group(1);
			messaging.convertAndSendToUser(username, "/queue/notifications",
					new Notification("You just got mentioned!"));
		}
	}
	
}

4、为目标用户发送消息

控制器中处理用户消息

  @MessageMapping("/spittle")
  @SendToUser("/queue/notifications")
  public Notification handleSpittle(Principal principal, SpittleForm form) {
	  Spittle spittle = new Spittle(principal.getName(), form.getText(), new Date());
	  spittleRepo.save(spittle);
	  feedService.broadcastSpittle(spittle);
	  return new Notification("Saved Spittle for user: " + principal.getName());
  }

UserDestinationMessageHandler主要任务是将用户消息重新路由到某个用户独有的目的地上。

为指定用户发送消息

convertAndSendToUser()

@Service
public class SpittleFeedServiceImpl implements SpittleFeedService {

	private SimpMessagingTemplate messaging;
	private Pattern pattern = Pattern.compile("\\@(\\S+)");
	
	@Autowired
	public SpittleFeedServiceImpl(SimpMessagingTemplate messaging) {
		this.messaging = messaging;
	}
	
	public void broadcastSpittle(Spittle spittle) {
		messaging.convertAndSend("/topic/spittlefeed", spittle);
		
		Matcher matcher = pattern.matcher(spittle.getMessage());
		if (matcher.find()) {
			String username = matcher.group(1);
			messaging.convertAndSendToUser(username, "/queue/notifications",
					new Notification("You just got mentioned!"));
		}
	}
	
}

5、处理消息异常

@MessageExceptionHandler(SpittleException.class)
@SendToUser("/queu/errors")
public SpittleException handleException(SpittleException e) {
  logger.error();
  return e;
}