直接上代码

后端：

首先建一个 Result 类

package com.ljv.chat.util;

import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

public class Result {
    public String clientId;
    public long timestamp;
    public SseEmitter sseEmitter;

    public Result(String clientId, long timestamp, SseEmitter sseEmitter) {
        this.clientId = clientId;
        this.timestamp = timestamp;
        this.sseEmitter = sseEmitter;
    }
}

然后创建一个 SseMap 类

package com.ljv.chat.util;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class SseMap {
    public static final Map<String, Result> sseEmitterMap = new ConcurrentHashMap<>();
}

创建 SaticScheduleTask 类 定时任务

package com.ljv.chat.util;

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class SaticScheduleTask {
    //3.添加定时任务
//    @Scheduled(cron = "0 0 3 * * ? ")


    @Scheduled(cron = "0 0 3 * * ? ")
    private void configureTasks() {
        SseMap.sseEmitterMap.clear();
    }
}

创建 SseEmitterController

package com.ljv.chat.test.controller;

import com.ljv.chat.util.Result;
import com.ljv.chat.util.SseMap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.CrossOrigin;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

/**
 * 服务器端实时推送技术之 SseEmitter 的用法测试
 * <p>
 * 测试步骤:
 * 1.请求http://localhost:8888/sse/start?clientId=111接口,浏览器会阻塞,等待服务器返回结果;
 * 2.请求http://localhost:8888/sse/send?clientId=111接口,可以请求多次,并观察第1步的浏览器返回结果;
 * 3.请求http://localhost:8888/sse/end?clientId=111接口结束某个请求,第1步的浏览器将结束阻塞;
 * 其中clientId代表请求的唯一标志;
 *
 * @author
 */

@CrossOrigin
@RestController
@RequestMapping("/web/sse")
public class SseEmitterController {
    private static final Logger logger = LoggerFactory.getLogger(SseEmitterController.class);

    // 用于保存每个请求对应的 SseEmitter


    /**
     * 返回SseEmitter对象
     *
     * @param clientId
     * @return
     */
    @RequestMapping("/start")
    public SseEmitter testSseEmitter(String clientId) {
        // 默认30秒超时,设置为0L则永不超时
        SseEmitter sseEmitter = new SseEmitter(0L);
        SseMap.sseEmitterMap.put(clientId, new Result(clientId, System.currentTimeMillis(), sseEmitter));
        return sseEmitter;
    }

    /**
     * 向SseEmitter对象发送数据
     *
     * @param clientId
     * @return
     */
    @RequestMapping("/send")
    public String setSseEmitter(String clientId) {
        try {
            Result result =  SseMap.sseEmitterMap.get(clientId);
            if (result != null && result.sseEmitter != null) {
                long timestamp = System.currentTimeMillis();
                String re = "{\"success\":true,\"message\":\"操作成功！\",\"code\":200,\"result\":{\"id\":1018},\"timestamp\":1629254216358}";
                result.sseEmitter.send(re);
            }
        } catch (IOException e) {
            logger.error("IOException!", e);
            return "error";
        }

        return "Succeed!";
    }

    /**
     * 将SseEmitter对象设置成完成
     *
     * @param clientId
     * @return
     */
    @RequestMapping("/end")
    public String completeSseEmitter(String clientId) {
        Result result =  SseMap.sseEmitterMap.get(clientId);
        if (result != null) {
            SseMap.sseEmitterMap.remove(clientId);
            result.sseEmitter.complete();
        }

        return "Succeed!";
    }

}

创建 ChatController

@CrossOrigin   //解决跨域
@RestController
@RequestMapping("chat")
public class ChatController {

   /**
    * 发送消息
    * @param homeId  房间id
    * @param msg   发送的消息
    * @param userId  用户id
    * @return
    */
   @GetMapping("send")
   public Result2<?> send(String homeId,String msg,String userId){

       for (String key :  SseMap.sseEmitterMap.keySet()) {
           if(key.indexOf(String.valueOf(homeId))!=-1){
               try{
                   Result result = SseMap.sseEmitterMap.get(key);
                   Map map=new HashMap();
                   map.put("msg",msg);
                   map.put("userId",userId);
                   String string = JSON.toJSONString(map);
                   result.sseEmitter.send(string);
               }catch (Exception e){
                   SseMap.sseEmitterMap.remove(key);
               }

           }
       }

       return Result2.OK("发送成功");
   }
}

前端（uniapp写的） 建立连接和关闭都是一样的，样式就是简单的测试使用

<template>
    <view class="content">
        <image class="logo" src="/static/logo.png"></image>
        <view class="text-area">
            <!-- <navigator :url="'/pages/index/chat?id='+homeId" hover-class="navigator-hover"> -->
                <button @click="join()"><text class="title">加入{{homeId}}房间</text></button>
            <!-- </navigator> -->
            <button @click="exit()"><text class="title">退出房间</text></button>
            <input v-if="send" type="text" v-model="msg" placeholder="请输入信息" style="border: 1rpx #4CD964 solid; border-radius: 10rpx;" />
            <button @click="sendMsg()">{{title}}</button>
        </view>
        <view v-if="getMsg!=null && getMsg!='' && !isMe">收到消息：<text style="color: red;">{{getMsg}}</text></view>
        <view v-if="getMsg!=null && getMsg!='' && isMe">发送消息：<text style="color: red;">{{getMsg}}</text> 成功</view>
    </view>
</template>

<script>
    export default {
        data() {
            return {
                title: '发送',
                randNum: '',
                msg:'',
                homeId: '1000',
                send: true,
                getMsg: '',
                isMe: false,
                                source:null,
            }
        },
        onLoad() {

        },
        onShow() {
            
        },
        onHide() {
            
        },
        methods: {
            sendMsg(){
                // alert("1")
                let self = this
                self.$http.get('/chat/send', {
                    homeId: self.homeId,
                    msg: self.msg,
                    userId: self.randNum
                }).then((res) => {
                    console.log(res.data)
                    
                });
            },
            exit(){
                // alert("2")
                this.close1();
            },
            join(){
                this.auto();
                // this.send=true
            },
            /**
             * 关闭连接
             */
            close1() {
                let self = this
                self.$http.get('/chat/end', {
                    clientId: self.randNum
                }).then((
                    res) => {
                        
                                                self.source.close();
                        uni.showToast({
                            title: '已退出房间',
                            duration: 2000
                        });
                    });
            },
            /**
             * 与服务器端建立连接
             */
            auto() {
                let self = this
                if (!!window.EventSource) {
                    this.randNum = this.homeId + this.uuid()
                    
                    self.source = new EventSource('http://localhost:8989/chat/start?clientId=' + this
                        .randNum);
                    uni.showToast({
                        title: '加入房间成功',
                        duration: 2000
                    });
                    self.source.onopen = function(event) {
                        console.log("链接建立")
                        
                    };
                    self.source.addEventListener('message', function(e) {
                        let data = JSON.parse(e.data)
                        console.log(data)
                        self.getMsg=data.msg
                        self.isMe=data.userId==self.randNum?true:false
                        // alert(data.message)
                    }, false);
                    self.source.addEventListener('error', function(e) {
                        console.log(e)
                    });
            
            
                } else {
                    alert("不支持sse")
                }
            },
            uuid() {
                var s = [];
                var hexDigits = "0123456789abcdef";
                for (var i = 0; i < 36; i++) {
                    s[i] = hexDigits.substr(Math.floor(Math.random() * 0x10), 1);
                }
                s[14] = "4"; // bits 12-15 of the time_hi_and_version field to 0010
                s[19] = hexDigits.substr((s[19] & 0x3) | 0x8, 1); // bits 6-7 of the clock_seq_hi_and_reserved to 01
                s[8] = s[13] = s[18] = s[23] = "-";
            
                var uuid = s.join("");
                return uuid;
            },
        }
    }
</script>

<style>
    .content {
        display: flex;
        flex-direction: column;
        align-items: center;
        justify-content: center;
    }

    .logo {
        height: 200rpx;
        width: 200rpx;
        margin-top: 200rpx;
        margin-left: auto;
        margin-right: auto;
        margin-bottom: 50rpx;
    }

    .text-area {
        display: flex;
        justify-content: center;
    }

    .title {
        font-size: 36rpx;
        color: #8f8f94;
    }
</style>