0. 前端代码

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8"/>
        <title>websocket通讯演示</title>
    </head>

    <body>

    <h3>发送消息</h3>
    <input type="text" id="msg"/>
    <input type="button" value="发送消息" id="sendMsg"/>

    <h3>接收消息</h3>
    <div id="receiveMsg" style="background-color: lightblue;">
    </div>

        <script type="application/javascript">
            window.CHAT = {
                socket: null,
                init: function () {
                    //判断当前浏览器是否支持websocket
                    if (window.WebSocket) {
                        //实例化webSocket
                        window.CHAT.socket = new WebSocket("ws://127.0.0.1:8080/ws");
                        //设置websocket的各个生命周期方法
                        window.CHAT.socket.onopen = function () {
                            console.log("建立连接");
                        },
                            window.CHAT.socket.onclose = function () {
                                console.log("连接关闭");
                            },
                            window.CHAT.socket.onerror = function () {
                                console.log("发生错误");
                            },
                            window.CHAT.socket.onmessage = function (e) {
                                console.log("接收到消息：" + e.data);
                                var receiveMsg = document.getElementById("receiveMsg");
                                var html = receiveMsg.innerHTML;
                                receiveMsg.innerHTML = html + "<br/>" + e.data;
                            }
                    } else {
                        alert("当前浏览器不支持webSocket，请升级！");
                    }
                },
                chat: function () {
                    var msg = document.getElementById("msg");
                    window.CHAT.socket.send(msg.value);
                }
            }
            window.CHAT.init();
            var sendMsg = document.getElementById("sendMsg");
            sendMsg.onclick = function () {
                window.CHAT.chat();
            }
        </script>
    </body>
</html>

?1. 引入依赖

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

2. 配置类

package com.janet;

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

/**
 * @Description TODO
 * @Author Janet
 * @Date 2022-05-09
 */
@Configuration
public class WebSocketConfig {

    /**
     * 扫描项目中带有@ServerEndpoint的注解，转成websocket服务实例
     * @return
     */
    @Bean
    public ServerEndpointExporter serverEndpointExporter(){
        return new ServerEndpointExporter();
    }

}

3. 服务类

package com.janet;

import io.netty.util.internal.ConcurrentSet;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @Description TODO
 * @Author Janet
 * @Date 2022-05-09
 */
@ServerEndpoint("/ws")
@Component
@Slf4j
public class WebSocketServer {
    /**
     * 在线人数
     */
    private static AtomicInteger personNum = new AtomicInteger();

    /**
     * 用来保存每个客户端对应的WebSocketServer实例
     */
    private static ConcurrentSet<WebSocketServer> webSocketSet = new ConcurrentSet<>();

    /**
     * 每个客户端对应的连接会话，通过它来主动给客户端发送消息
     */
    private Session session;


    /**
     * 当连接建立成功之后，会调用该方法
     *
     * @param session
     */
    @OnOpen
    public void onOpen(Session session) {
        this.session = session;
        webSocketSet.add(this);
        personNum.incrementAndGet();
        log.info("新用户上线，当前在线人数:{}", personNum.get());
    }


    @OnClose
    public void onClose() {
        webSocketSet.remove(this);
        personNum.decrementAndGet();
        log.info("用户下线，当前在线人数:{}", personNum.get());
    }


    @OnMessage
    public void onMessage(String message, Session session) throws IOException {
        log.info("来自客户{}的消息：{}", session.getId(), message);
        for (WebSocketServer webSocketServer : webSocketSet) {
            webSocketServer.session.getBasicRemote().sendText(session.getId() + "说：" + message);
        }
    }

}

这样就ok啦~