Question

我目前有一个带有STOMP设置的简单WebSocket，客户端将其连接到主题（具有ID）。控制器立即响应要求的内容，并设置了一个变量来指示客户端已订阅的内容。现在，带有@Scheduled注释的方法每隔几秒钟就会向客户端发送一次请求。

在客户端第一次连接之前，计划的方法不会执行任何操作。但是，在第一次订阅后，无论是否订阅了客户端，它将继续发布。

@Controller
public class ServiceWebSocketController {

    @Autowired
    private ServiceService serviceService;

    @Autowired
    WebSocketSessionController webSocketSessionController;

    @Autowired
    private SimpMessagingTemplate simpMessagingTemplate;

    private Set<Long> services = new HashSet<>();

    @SubscribeMapping("/service/{serviceId}")
    public ServiceDTO subscribe(@DestinationVariable("serviceId") final Long serviceId) throws SQLException {
        System.out.println("Subscribed to Service with ID: " + serviceId);
        services.add(serviceId);
        return serviceService.getServiceWithProperties(serviceId).orElseThrow(() -> new ResourceNotFoundException("Service", "id", serviceId));
    }

    @Scheduled(fixedDelay = 2000)
    public void service() throws SQLException {
        services.removeIf(serviceId -> !webSocketSessionController.hasSubscriptionTo("/topic/service/" + serviceId));

        // Publish specified Service data to each anonymously subscribed client.
        services.forEach(serviceId -> {
            try {
                System.out.println("Publishing Service with ID: " + serviceId);
                // We don't use .convertAndSendToUser here, because all our clients are anonymous.
                simpMessagingTemplate.convertAndSend("/topic/service/" + serviceId, serviceService.getServiceWithProperties(serviceId));
            } catch (SQLException e) {
                e.printStackTrace();
            }
        });
    }
}

如何确定客户是否已取消订阅？如果存在类似于@UnsubscribeMapping的东西，我可以简单地再次将currentSubscriptionServiceId变量设置为null，以防止计划的方法连续发布数据。

Answer 1

您可以像这样监听事件SessionUnsubscribeEvent：

@Controller
public class SessionUnsubscribeListener implements ApplicationListener<SessionUnsubscribeEvent> {

   @Override
   public void onApplicationEvent(SessionUnsubscribeEvent event) {
       GenericMessage message = (GenericMessage) event.getMessage();

       String simpDestination = (String) message.getHeaders().get("simpDestination");

       if ("/topic/service".equals(simpDestination)) {
           // do stuff
       }
   }
}

Spring Boot WebSocket：我如何知道客户端何时取消订阅？

1 个答案: