WebSocket协议是基于TCP的一种新的网络协议。它实现了浏览器与服务器全双工(full-duplex)通信——允许服务器主动发送信息给客户端。

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1、新建SpringBoot项目

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2、pom.xml依赖

<?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>2.2.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.wzf</groupId>
    <artifactId>websocket</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>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-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
            <version>2.2.1.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

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

3、WebSocketConfig.java

启用WebSocket的支持也是很简单，几句代码搞定

package com.wzf.websocket;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;

@Configuration
public class WebSocketConfig {

    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}

4、WebSocketServer.java

因为WebSocket是类似客户端服务端的形式(采用ws协议)，那么这里的WebSocketServer其实就相当于一个ws协议的Controller，直接@ServerEndpoint("/websocket")，@Component启用即可，然后在里面实现@OnOpen，@onClose，@onMessage等方法

package com.wzf.websocket;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.CopyOnWriteArraySet;

@Slf4j
@ServerEndpoint("/websocket/{sid}")
@Component
public class WebSocketServer {

    //静态变量，用来记录当前在线连接数。应该把它设计成线程安全的。
    private static int onlineCount = 0;

    //concurrent包的线程安全Set，用来存放每个客户端对应的MyWebSocket对象。
    private static CopyOnWriteArraySet<WebSocketServer> webSocketSet = new CopyOnWriteArraySet<WebSocketServer>();

    //与某个客户端的连接会话，需要通过它来给客户端发送数据
    private Session session;

    //接收sid
    private String sid="";

    /**
     * 连接建立成功调用的方法*/
    @OnOpen
    public void onOpen(Session session,@PathParam("sid") String sid) throws InterruptedException {
        this.session = session;
        webSocketSet.add(this);     //加入set中
        addOnlineCount();           //在线数加1
        log.info("有新窗口开始监听:"+sid+",当前在线人数为" + getOnlineCount());
        this.sid=sid;
        try {
            //模拟服务器向客户端发消息(群发)
            sendMessage("连接成功");

            //模拟服务器向客户端发消息(某一20客户端)
            for(int i = 0; i<5; i++){
                Thread.sleep(1000);
                sendInfo(String.valueOf(i), "20");
            }
        } catch (IOException e) {
            log.error("websocket IO异常");
        }
    }

    /**
     * 连接关闭调用的方法
     */
    @OnClose
    public void onClose() {
        webSocketSet.remove(this);  //从set中删除
        subOnlineCount();           //在线数减1
        log.info("有一连接关闭！当前在线人数为" + getOnlineCount());
    }

    /**
     * 收到客户端消息后调用的方法
     *
     * @param message 客户端发送过来的消息*/
    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("收到来自窗口"+sid+"的信息:"+message);
        //群发消息
        for (WebSocketServer item : webSocketSet) {
            try {
                item.sendMessage(message);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     *连接发生错误时
     * @param session
     * @param error
     */
    @OnError
    public void onError(Session session, Throwable error) {
        log.error("发生错误");
//        error.printStackTrace();
    }
    /**
     * 实现服务器主动推送
     */
    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }


    /**
     * 实现服务器主动向某一客户端推送消息
     * */
    public static void sendInfo(String message,@PathParam("sid") String sid) throws IOException {
        log.info("推送消息到窗口"+sid+"，推送内容:"+message);
        for (WebSocketServer item : webSocketSet) {
            try {
                //这里可以设定只推送给这个sid的，为null则全部推送
                if(sid==null) {
                    item.sendMessage(message);
                }else if(item.sid.equals(sid)){
                    item.sendMessage(message);
                }
            } catch (IOException e) {
                continue;
            }
        }
    }

    public static synchronized int getOnlineCount() {
        return onlineCount;
    }

    public static synchronized void addOnlineCount() {
        WebSocketServer.onlineCount++;
    }

    public static synchronized void subOnlineCount() {
        WebSocketServer.onlineCount--;
    }
}

5、客户端 test1.html (sid=20)

<html>
    <head></head>
    <body>
        <div id="messageId"></div>
        
        <script>
            var socket;  
            if(typeof(WebSocket) == "undefined") {  
                console.log("您的浏览器不支持WebSocket");  
            }else{  
                console.log("您的浏览器支持WebSocket");  
                //实现化WebSocket对象，指定要连接的服务器地址与端口  建立连接  
                socket = new WebSocket("ws://localhost:8080/websocket/20");  
                //打开事件  
                socket.onopen = function() {  
                    console.log("Socket 已打开");  
                    //socket.send("这是来自客户端的消息" + location.href + new Date());  
                };  
                //获得消息事件  
                socket.onmessage = function(msg) {  
                    console.log(msg.data);  
                    //发现消息进入    开始处理前端触发逻辑
                    let msgDiv = document.getElementById("messageId");
                    msgDiv.innerHTML = msg.data;
                };  
                //关闭事件  
                socket.onclose = function() {  
                    console.log("Socket已关闭");  
                };  
                //发生了错误事件  
                socket.onerror = function() {  
                    alert("Socket发生了错误");  
                    //此时可以尝试刷新页面
                }  
            }
        </script>
    </body>
</html>

6、客户端 test2.html (sid=30)

<html>
    <head></head>
    <body>
        <div id="messageId"></div>
        
        <script>
            var socket;  
            if(typeof(WebSocket) == "undefined") {  
                console.log("您的浏览器不支持WebSocket");  
            }else{  
                console.log("您的浏览器支持WebSocket");  
                //实现化WebSocket对象，指定要连接的服务器地址与端口  建立连接  
                socket = new WebSocket("ws://localhost:8080/websocket/30");  
                //打开事件  
                socket.onopen = function() {  
                    console.log("Socket 已打开");  
                    //socket.send("这是来自客户端的消息" + location.href + new Date());  
                };  
                //获得消息事件  
                socket.onmessage = function(msg) {  
                    console.log(msg.data);  
                    //发现消息进入    开始处理前端触发逻辑
                    let msgDiv = document.getElementById("messageId");
                    msgDiv.innerHTML = msg.data;
                };  
                //关闭事件  
                socket.onclose = function() {  
                    console.log("Socket已关闭");  
                };  
                //发生了错误事件  
                socket.onerror = function() {  
                    alert("Socket发生了错误");  
                    //此时可以尝试刷新页面
                }  
            }
        </script>
    </body>
</html>

7、启动SpringBoot程序，然后分别在两个不同的窗口中打开test1.html和test2.html页面。效果如下：

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