SSE（Server-Sent Events）是一种基于HTTP的实时通信协议，它允许服务器向客户端发送持久性的数据流。与WebSocket不同的是，SSE是单向通信，只能由服务器向客户端发送数据。Spring Boot通过Spring WebFlux模块提供了对SSE的支持。下面是一个简单的示例：
1、后端

package com.example.springbootmp.controller;import lombok.SneakyThrows;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;import java.io.IOException;
import java.util.Map;
import java.util.concurrent.*;@Controller
@RequestMapping(path = "sse")
@CrossOrigin("*")
public class SseRest {private final static Map<String, SseEmitter> sseCache = new ConcurrentHashMap<>();/*** 连接sse服务，并向前端推送数据* @param id* @return* @throws IOException*/@GetMapping(path = "subscribe", produces = {MediaType.TEXT_EVENT_STREAM_VALUE})@SneakyThrowspublic SseEmitter push(String id) throws IOException {// 超时时间设置为5分钟，用于演示客户端自动重连SseEmitter sseEmitter = new SseEmitter(5_60_000L);// 设置前端的重试时间为1ssseCache.put(id, sseEmitter);ExecutorService executorService= Executors.newFixedThreadPool(1,(Runnable r)->{Thread t=new Thread(r);t.setDaemon(true);return t;});SseEmitter.SseEventBuilder data = SseEmitter.event().name("message").id(id).data("测试数据");executorService.execute(()->{while (true){if(sseCache.containsKey(id)){System.out.println("发送");try {sseEmitter.send(data);Thread.sleep(2000);} catch (IOException e) {e.printStackTrace();}catch (InterruptedException e) {e.printStackTrace();}}else {System.out.println("结束");break;}}});//        while (true){
//            sseEmitter.send("测试数据",MediaType.APPLICATION_JSON);
//            Thread.sleep(1000);
//        }// onCompletion(): 结束之后的回调触发//sseEmitter.onCompletion(() -> System.out.println("完成！！！"));return sseEmitter;}/*** http://127.0.0.1:8080/sse/push?id=7777&content=%E4%BD%A0%E5%93%88aaaaaa* @param id* @param content* @return* @throws IOException*/@ResponseBody@GetMapping(path = "push")public String push(String id, String content) throws IOException {SseEmitter sseEmitter = sseCache.get(id);if (sseEmitter != null) {sseEmitter.send(content);}return "over";}@ResponseBody@GetMapping(path = "/over/{id}")public String over(@PathVariable("id") String id) {SseEmitter sseEmitter = sseCache.get(id);if (sseEmitter != null) {// complete(): 表示执行完毕，会断开连接sseEmitter.complete();sseCache.remove(id);}return "over";}
}

2、前端

var source
//开始建立连接部分
source = new EventSource('http://localhost:9999/sse/subscribe?id=122')source.addEventListener('message',function(event) {console.log('接收数据')console.log(event.data)},false)
//关闭连接部分
source.close()