WebSocket 协议简介

WebSocket 协议提供了一种标准化的方式，在客户端和服务端建立在一个TCP 连接之上的全双工，双向通信的协议。

WebSocket 交互开始于 HTTP 请求，使用 HTTP 请求的 header 中的 Upgrade 进行切换到 WebSocket 协议。

HTTP 和 WebSocket 对比

即使 WebSocket 的设计兼容 HTTP 协议和开始于 HTTP 请求，了解两个协议是不同架构和应用模型是非常重要的。

在 HTTP 和 REST， 一个应用有多个URL， 对于交互的应用，客户端可以访问这些 URL，请求和响应的风格。服务端会根据 URL、http method、header 等等信息进行路由处理。

相比之下， WebSocket 协议是使用一个URL 初始化连接。应用所有的消息通过同一个 TCP 通信，这一点是完全不同的异步、事件驱动的消息传递体系结构。

WebSocket API 的使用

1. Webflux 依赖

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

2. 定义一个Handler，用于处理数据的请求和响应

import java.time.Duration;
import org.springframework.web.reactive.socket.WebSocketHandler;
import org.springframework.web.reactive.socket.WebSocketMessage;
import org.springframework.web.reactive.socket.WebSocketSession;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

public class MyWebSocketHandler implements WebSocketHandler {
// 每间隔 1 秒，数字加 1
  private Flux<Long> intervalFlux = Flux.interval(Duration.ofSeconds(1L), Duration.ofSeconds(1L));

  @Override
  public Mono<Void> handle(WebSocketSession session) {
    return session.send(intervalFlux.map(item -> session.textMessage(item + "")))
        .and(session.receive().map(WebSocketMessage::getPayloadAsText).log());
  }
}

3. 配置类，配置 WebSocket 的 URL 信息

@Configuration
public class WebConfig {

  @Bean
  public WebSocketHandlerAdapter handlerAdapter() {
    return new WebSocketHandlerAdapter();
  }

  @Bean
  public HandlerMapping handlerMapping() {
    Map<String, WebSocketHandler> urlMap = new HashMap<>();
    urlMap.put("/path", new MyWebSocketHandler());
    int order = -1;
    return new SimpleUrlHandlerMapping(urlMap, order);
  }
}

4. 客户端

import java.net.URI;
import java.net.URISyntaxException;
import java.time.Duration;
import org.springframework.web.reactive.socket.WebSocketMessage;
import org.springframework.web.reactive.socket.client.ReactorNettyWebSocketClient;
import org.springframework.web.reactive.socket.client.WebSocketClient;
import reactor.core.publisher.Mono;

public class Client {

  public static void main(String[] args) throws URISyntaxException {

    WebSocketClient client = new ReactorNettyWebSocketClient();
    URI url = new URI("ws://localhost:8080/path");
    client.execute(url,
        session -> session.send(Mono.just(session.textMessage("hello world")))
            .thenMany(session.receive().map(WebSocketMessage::getPayloadAsText).log())
            .then())
        .block(Duration.ofSeconds(10));
  }
}

服务端日志

2021-08-10 22:42:36.162  INFO 85792 --- [           main] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8080
2021-08-10 22:42:36.168  INFO 85792 --- [           main] c.e.s.SpringBootDemoApplication          : Started SpringBootDemoApplication in 3.583 seconds (JVM running for 4.462)
2021-08-10 22:42:51.518  INFO 85792 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : onSubscribe(FluxMap.MapSubscriber)
2021-08-10 22:42:51.522  INFO 85792 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : request(unbounded)
2021-08-10 22:42:51.534  INFO 85792 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : onNext(hello world)
2021-08-10 22:43:00.956  INFO 85792 --- [ctor-http-nio-2] reactor.Flux.Map.1                       : onComplete()

客户端日志

22:42:51.527 [reactor-http-nio-1] DEBUG reactor.netty.channel.FluxReceive - [id: 0xd95be56c, L:/127.0.0.1:50773 - R:localhost/127.0.0.1:8080] Subscribing inbound receiver [pending: 0, cancelled:false, inboundDone: false]
22:42:51.530 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onSubscribe(FluxMap.MapSubscriber)
22:42:51.531 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - request(unbounded)
22:42:52.518 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(0)
22:42:53.513 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(1)
22:42:54.518 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(2)
22:42:55.513 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(3)
22:42:56.514 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(4)
22:42:57.516 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(5)
22:42:58.518 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(6)
22:42:59.512 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(7)
22:43:00.513 [reactor-http-nio-1] INFO reactor.Flux.Map.1 - onNext(8)
22:43:00.947 [main] INFO reactor.Flux.Map.1 - cancel()
22:43:00.948 [reactor-http-nio-1] DEBUG reactor.netty.http.client.HttpClientOperations - [id: 0xd95be56c, L:/127.0.0.1:50773 - R:localhost/127.0.0.1:8080] Cancelling Websocket inbound. Closing Websocket
Exception in thread "main" java.lang.IllegalStateException: Timeout on blocking read for 10000 MILLISECONDS

至此，Spring WebFlux 中 WebSocket 协议使用的结束了。