Spring WebSocket：在 ChannelInterceptor 内部使用 SimpUserRegistry 而不创建依赖循环

Question

我的目标是使用 SimpUserRegistry 检查有多少用户订阅了一个主题以限制订阅数量。 为了测试我的代码，我使用了基本的https://spring.io/guides/gs/messaging-stomp-websocket/项目。

这是我对该项目的唯一更改：

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
    @Autowired
    private TopicSubscriptionInterceptor topicSubscriptionInterceptor
    ...
    
    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.interceptors(topicSubscriptionInterceptor);
    }
}

//-------------------------------------------- --------------------------------------

@Component
public class TopicSubscriptionInterceptor implements ChannelInterceptor {
    
    @Autowired 
    private SimpUserRegistry userRegistry;
    
    @Override
    public Message<?> preSend(Message<?> message, MessageChannel channel){              
        // ... use SimpUserRegistry to check amount of users subscribed to a topic and whether 
        // or not to allow a subscription (throw exception/null)

    }

//-------------------------------------------- --------------------------------------

我试图只传递一个new TopicSubscriptionInterceptor()而不是使用 @Autowired 将其添加为依赖项，但这显然使 TopicSubscriptionInterceptor null 中的所有依赖项。

//-------------------------------------------- ---

依赖循环：

┌─────┐
|  webSocketConfig (field private com.xxx.yyy.interceptor.TopicSubscriptionInterceptor com.xxx.yyy.config.WebSocketConfig.topicSubscriptionInterceptor)
↑     ↓
|  topicSubscriptionInterceptor (field private org.springframework.messaging.simp.user.SimpUserRegistry com.xxx.yyy.interceptor.TopicSubscriptionInterceptor.userRegistry)
↑     ↓
|  org.springframework.web.socket.config.annotation.DelegatingWebSocketMessageBrokerConfiguration
└─────┘

这是我试过的编辑（1）：

    @Configuration
    @EnableWebSocketMessageBroker
    public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
        @Bean
        public TopicSubscriptionInterceptor 
            myTopicSubscriptionInterceptor(){
                return new TopicSubscriptionInterceptor();
        }

        ...
        
        @Override
        public void configureClientInboundChannel(ChannelRegistration registration) {
            registration.interceptors(myTopicSubscriptionInterceptor());
        }
    }

Answer 1

使用 Lazy Initialization 解决了这个问题，尽管它感觉像是一个创可贴解决方案。 我不确定是否还有其他更好的方法，因为我是 Spring 的新手。

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

    private TopicSubscriptionInterceptor topicSubscriptionInterceptor;
    
    @Autowired
    public WebSocketConfig(@Lazy TopicSubscriptionInterceptor topicSubscriptionInterceptor) {
        this.topicSubscriptionInterceptor = topicSubscriptionInterceptor;
    }

    ...
    
    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.interceptors(topicSubscriptionInterceptor);
    }
}