[网络协议]使用WebSocket建立交互式的Web应用

Using WebSocket to build an interactive web application

简介

建立Hello,world应用，在浏览器和服务器之间发送消息。WebSocket是轻量的再TCP之上的一层。这使他可以使用子协议嵌入消息。这里例子，我们使用Spring的STOMP消息创建一个交互的web应用。

1.目标

你会建立一个服务来接收消息，这里是接收用户姓名。服务会将问候的消息存放到队列中，返回给用户。

pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.4.3</version>
    <relativePath/> <!-- lookup parent from repository -->
  </parent>
  <groupId>com.example</groupId>
  <artifactId>messaging-stomp-websocket</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>messaging-stomp-websocket</name>
  <description>Demo project for Spring Boot</description>
  <properties>
    <java.version>1.8</java.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-websocket</artifactId>
    </dependency>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator-core</artifactId>
    </dependency>
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>sockjs-client</artifactId>
      <version>1.0.2</version>
    </dependency>
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>stomp-websocket</artifactId>
      <version>2.3.3</version>
    </dependency>
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>bootstrap</artifactId>
      <version>3.3.7</version>
    </dependency>
    <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>jquery</artifactId>
      <version>3.1.1-1</version>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
    </plugins>
  </build>

</project>

?服务端接收的消息格式为

{
    "name": "Fred"
}

新建src/main/java/com/example/messagingstompwebsocket/HelloMessage.java类来存储数据name。

package com.example.messagingstompwebsocket;

public class HelloMessage {

  private String name;

  public HelloMessage() {
  }

  public HelloMessage(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }
}

返回的消息格式为

{
    "content": "Hello, Fred!"
}

新建src/main/java/com/example/messagingstompwebsocket/Greeting.java来存储数据content。

package com.example.messagingstompwebsocket;

public class Greeting {

  private String content;

  public Greeting() {
  }

  public Greeting(String content) {
    this.content = content;
  }

  public String getContent() {
    return content;
  }

}

Spring会使用 Jackson JSON库来自动将对象转为JSON，JSON转为对象。

新建src/main/java/com/example/messagingstompwebsocket/GreetingController.java用来处理消息。

package com.example.messagingstompwebsocket;

import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.messaging.handler.annotation.SendTo;
import org.springframework.stereotype.Controller;
import org.springframework.web.util.HtmlUtils;

@Controller
public class GreetingController {


  @MessageMapping("/hello")
  @SendTo("/topic/greetings")
  public Greeting greeting(HelloMessage message) throws Exception {
    Thread.sleep(1000); // simulated delay
    return new Greeting("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!");
  }

}

?@MessageMapping，一个消息发送到/hello，greeting方法会被调用。

greeting()，HelloMessage的对象message会接收到传递过来的消息。1秒钟的延迟之后greeting方法创建一个Greeting对象返回。

@SendTo，该返回值会广播到所有订阅者为/topic/greetings的那里去。

配置STOMP消息

新建src/main/java/com/example/messagingstompwebsocket/WebSocketConfig.java

package com.example.messagingstompwebsocket;

import org.springframework.context.annotation.Configuration;
import org.springframework.messaging.simp.config.MessageBrokerRegistry;
import org.springframework.web.socket.config.annotation.EnableWebSocketMessageBroker;
import org.springframework.web.socket.config.annotation.StompEndpointRegistry;
import org.springframework.web.socket.config.annotation.WebSocketMessageBrokerConfigurer;

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

  @Override
  public void configureMessageBroker(MessageBrokerRegistry config) {
    config.enableSimpleBroker("/topic");
    config.setApplicationDestinationPrefixes("/app");
  }

  @Override
  public void registerStompEndpoints(StompEndpointRegistry registry) {
    registry.addEndpoint("/gs-guide-websocket").withSockJS();
  }

}

?@Configuration，说明该类为Spring配置类。

@EnableWebSocketMessageBroker，表示使用WebSocket处理消息，使用消息代理来返回消息。

enableSimpleBroker("/topic")，启用一个简单的基于内存消息代理将问候的信息返回给客户端?

/topic，是过滤目标消息代理的标志。?

config.setApplicationDestinationPrefixes("/app")，stomp客户端发送消息时指定的endpoint。

registry.addEndpoint("/gs-guide-websocket").withSockJS()，启用SockJS回退选项，以便在WebSocket不可用时可以使用备用传输。

新建src/main/resources/static/index.html

<!DOCTYPE html>
<html>
<head>
  <title>Hello WebSocket</title>
  <link href="/webjars/bootstrap/css/bootstrap.min.css" rel="stylesheet">
  <link href="/main.css" rel="stylesheet">
  <script src="/webjars/jquery/jquery.min.js"></script>
  <script src="/webjars/sockjs-client/sockjs.min.js"></script>
  <script src="/webjars/stomp-websocket/stomp.min.js"></script>
  <script src="/app.js"></script>
</head>
<body>
<noscript><h2 style="color: #ff0000">Seems your browser doesn't support Javascript! Websocket relies on Javascript being
  enabled. Please enable
  Javascript and reload this page!</h2></noscript>
<div id="main-content" class="container">
  <div class="row">
    <div class="col-md-6">
      <form class="form-inline">
        <div class="form-group">
          <label for="connect">WebSocket connection:</label>
          <button id="connect" class="btn btn-default" type="submit">Connect</button>
          <button id="disconnect" class="btn btn-default" type="submit" disabled="disabled">Disconnect
          </button>
        </div>
      </form>
    </div>
    <div class="col-md-6">
      <form class="form-inline">
        <div class="form-group">
          <label for="name">What is your name?</label>
          <input type="text" id="name" class="form-control" placeholder="Your name here...">
        </div>
        <button id="send" class="btn btn-default" type="submit">Send</button>
      </form>
    </div>
  </div>
  <div class="row">
    <div class="col-md-12">
      <table id="conversation" class="table table-striped">
        <thead>
        <tr>
          <th>Greetings</th>
        </tr>
        </thead>
        <tbody id="greetings">
        </tbody>
      </table>
    </div>
  </div>
</div>
</body>
</html>

?这里HTML文件，导入了SockJS和STOMP的js库，来与我们的服务端STOMP通信。

新建src/main/resources/static/app.js

var stompClient = null;

function setConnected(connected) {
    $("#connect").prop("disabled", connected);
    $("#disconnect").prop("disabled", !connected);
    if (connected) {
        $("#conversation").show();
    }
    else {
        $("#conversation").hide();
    }
    $("#greetings").html("");
}

function connect() {
    var socket = new SockJS('/gs-guide-websocket');
    stompClient = Stomp.over(socket);
    stompClient.connect({}, function (frame) {
        setConnected(true);
        console.log('Connected: ' + frame);
        stompClient.subscribe('/topic/greetings', function (greeting) {
            showGreeting(JSON.parse(greeting.body).content);
        });
    });
}

function disconnect() {
    if (stompClient !== null) {
        stompClient.disconnect();
    }
    setConnected(false);
    console.log("Disconnected");
}

function sendName() {
    stompClient.send("/app/hello", {}, JSON.stringify({'name': $("#name").val()}));
}

function showGreeting(message) {
    $("#greetings").append("<tr><td>" + message + "</td></tr>");
}

$(function () {
    $("form").on('submit', function (e) {
        e.preventDefault();
    });
    $( "#connect" ).click(function() { connect(); });
    $( "#disconnect" ).click(function() { disconnect(); });
    $( "#send" ).click(function() { sendName(); });
});

?connect()，使用SockJS和stomp.js连接到/gs-guide-websocket，连接成功后，客户端会订阅/topic/greetings消息。

sendName()，取回用户输入的名称，使用STOMP客户端将他发送到/app/hello，这里就是GreetingController.greeting()会接收它。

新建src/main/java/com/example/messagingstompwebsocket/MessagingStompWebsocketApplication.java

package com.example.messagingstompwebsocket;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MessagingStompWebsocketApplication {

  public static void main(String[] args) {
    SpringApplication.run(MessagingStompWebsocketApplication.class, args);
  }
}

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