Spring Boot 中使用 WebSocket

ゝ一纸荒年。 2022-01-05 07:25 270阅读 0赞

# Spring Boot 中使用 WebSocket #

> WebSocket 是一种长连接技术，可以实现服务端和客户端的双向通信，服务端可以主动推送信息给客户端

## 构建应用 ##

### 添加依赖 ###

*  build.gradle

dependencies {
        compile("org.springframework.boot:spring-boot-starter-websocket")
        compile("org.webjars:webjars-locator-core")
        compile("org.webjars:sockjs-client:1.0.2")
        compile("org.webjars:stomp-websocket:2.3.3")
        compile("org.webjars:bootstrap:3.3.7")
        compile("org.webjars:jquery:3.1.0")
    
        testCompile("org.springframework.boot:spring-boot-starter-test")
    }

### 配置 ###

*  WebSocketConfig.java

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

其中`/topic` 是用于推送给客户端的消息路径前缀；`/app`是用于请求服务端的消息路径前缀， `/socket`用于客户端建立连接

SockJS用于提供浏览器兼容性，当浏览器不支持 WebSocket 时，就会尝试降级为HTTP流或者长轮询的方式以实现和 WebSocket 相同的效果，参考 [4.3. SockJS Fallback][]

### 群发消息 ###

群发消息可以将消息发送给所有订阅了该消息的客户端，可以通过 `@SendTo`或`org.springframework.messaging.simp.SimpMessagingTemplate#convertAndSend`发送

#### 服务端 ####

*  通过注解实现

@MessageMapping("/message/broadcast")
        @SendTo("/response/message")
        public Message broadcastMessage(String title) { 
            log.info("Receive new broadcast message from socket, title is :" + title);
    
            return Message.builder()
                          .title(title)
                          .content("Socket Broadcast:" + title + " content!")
                          .createTime(LocalDateTime.now())
                          .build();
        }

*  通过 REST接口调用方法实现

@Autowired
        private SimpMessagingTemplate simpMessagingTemplate;
    
        @GetMapping("/message/broadcast")
        @ResponseBody
        public void sendBroadcastMessage(String title) { 
            log.info("Receive new broadcast message from REST interface, title is :" + title);
    
            Message message = Message.builder()
                                     .title(title)
                                     .content("REST Broadcast:" + title + " content!")
                                     .createTime(LocalDateTime.now())
                                     .build();
    
            simpMessagingTemplate.convertAndSend("/response/message", message);
        }

#### 客户端 ####

#### 测试 ####

*  启动应用，用两个不同的浏览器访问 localhost:8080
 *  广播消息建立连接，并发送消息，此时可以看到两个浏览器都收到了刚才发送的消息
 *  通过 REST 接口：

curl 'localhost:8080/message/broadcast?title=hello'

### 发送给指定客户端 ###

群发消息可以将消息发送给所有订阅了该消息的客户端，可以通过 `@SendToUser`或`org.springframework.messaging.simp.SimpMessagingTemplate#convertAndSendToUser`发送

#### 服务端 ####

发送给指定客户端，要求客户端有指定的用户名，通过继承`org.springframework.web.socket.server.support.DefaultHandshakeHandler`实现

*  CustomPrinciple.java

@AllArgsConstructor
    public class CustomPrinciple implements Principal { 
    
        private String name;
    
        @Override
        public String getName() { 
            return this.name;
        }
    }

*  CustomHandshakeHandler.java

@Slf4j
    public class CustomHandshakeHandler extends DefaultHandshakeHandler { 
    
        @Override
        protected Principal determineUser(ServerHttpRequest request, WebSocketHandler wsHandler, Map<String, Object> attributes) { 
            String userId = UUID.randomUUID().toString();
            log.info("Current username is: {}", userId);
            return new CustomPrinciple(userId);
        }
    }

*  WebSocketConfig.java

@Override
        public void registerStompEndpoints(StompEndpointRegistry registry) { 
            registry.addEndpoint("/socket")
                    .setHandshakeHandler(new CustomHandshakeHandler())
                    .withSockJS();
    
        }

*  通过注解实现

@MessageMapping("/message/specify")
        @SendToUser("/response/message")
        public Message speicifyMessage(String title) { 
            log.info("Receive new specify message from socket, title is :" + title);
    
            return Message.builder()
                          .title(title)
                          .content("Socket Specify:" + title + " content!")
                          .createTime(LocalDateTime.now())
                          .build();
        }

*  通过调用方法实现

@GetMapping("/message/specify")
        @ResponseBody
        public void sendSpecifyUserMessage(String title, String username) { 
            log.info("Receive new specify message from REST interface, title is :" + title);
    
            Message message = Message.builder()
                                     .title(title)
                                     .content("REST Specify:" + title + " content!")
                                     .createTime(LocalDateTime.now())
                                     .build();
    
            simpMessagingTemplate.convertAndSendToUser(username, "/response/message", message);
        }

#### 客户端 ####

需要注意的是，发送给指定用户的消息订阅时需要添加额外的 `/user`前缀

#### 测试 ####

*  启动应用，用两个不同的浏览器访问 localhost:8080
 *  指定消息建立连接，并发送消息，此时只有发送消息的那个浏览器才能收到消息，另一个没有收到
 *  通过 REST 接口：  
    建立连接后可以在控制台看到相应的 username

curl 'localhost:8080/message/specify?title=hello&username=ff3cb2ca-9579-46fb-973b-b1bd6420f610'

此时相应的客户端会收到发送的消息，而另一个没有

--------------------

### 参考文档 ###

*  [Using WebSocket to build an interactive web application][]
 *  [Spring Boot + WebSockets + Angular 5][Spring Boot _ WebSockets _ Angular 5]
 *  [Spring MVC 3.2 Preview: Techniques for Real-time Updates][Spring MVC 3.2 Preview_ Techniques for Real-time Updates]

### 项目地址 ###

*  [https://github.com/helloworlde/SpringBootCollection/tree/master/SpringBoot-WebSocket][https_github.com_helloworlde_SpringBootCollection_tree_master_SpringBoot-WebSocket]

[4.3. SockJS Fallback]: https://docs.spring.io/spring/docs/5.1.8.RELEASE/spring-framework-reference/web.html#websocket-fallback
[Using WebSocket to build an interactive web application]: https://spring.io/guides/gs/messaging-stomp-websocket/
[Spring Boot _ WebSockets _ Angular 5]: https://medium.com/oril/spring-boot-websockets-angular-5-f2f4b1c14cee
[Spring MVC 3.2 Preview_ Techniques for Real-time Updates]: https://spring.io/blog/2012/05/08/spring-mvc-3-2-preview-techniques-for-real-time-updates/
[https_github.com_helloworlde_SpringBootCollection_tree_master_SpringBoot-WebSocket]: https://github.com/helloworlde/SpringBootCollection/tree/master/SpringBoot-WebSocket