java通过SSE实现消息推送

一、什么是SSE

严格地说,HTTP 协议无法做到服务器主动推送信息。但是,有一种变通方法,就是服务器向客户端声明,接下来要发送的是流信息(streaming)。

也就是说,发送的不是一次性的数据包,而是一个数据流,会连续不断地发送过来。这时,客户端不会关闭连接,会一直等着服务器发过来的新的数据流,视频播放就是这样的例子。本质上,这种通信就是以流信息的方式,完成一次用时很长的下载。

SSE 就是利用这种机制,使用流信息向浏览器推送信息。它基于 HTTP 协议,目前除了 IE,其他浏览器都支持。

二、如何在java中实现SSE

在Spring Boot项目中,无需额外引入特定的依赖,因为Spring Web MVC模块已经内置了对SSE的支持。

1、编写SSE服务,来进行创建链接和发送消息

package com.smart3dmap.prjpntmanage.service;

import lombok.extern.slf4j.Slf4j;
import org.apache.commons.lang3.StringUtils;
import org.springframework.stereotype.Service;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

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

@Slf4j
@Service
public class SSEService {
    private static final Map<String,SseEmitter> sseEmitterMap = new ConcurrentHashMap<>();
    public SseEmitter crateSse(String uid) {
        SseEmitter sseEmitter = new SseEmitter(0L);
        sseEmitter.onCompletion(() -> {
            log.info("[{}]结束链接" , uid);
            sseEmitterMap.remove(uid);
        });
        sseEmitter.onTimeout(() -> {
            log.info("[{}]链接超时",uid);
        });
        sseEmitter.onError(throwable -> {
            try{
                log.info("[{}]链接异常,{}",uid,throwable.toString());
                sseEmitter.send(SseEmitter.event()
                        .id(uid)
                        .name("发生异常")
                        .data("发生异常请重试")
                        .reconnectTime(3000));
                sseEmitterMap.put(uid,sseEmitter);
            }catch (IOException e){
                e.printStackTrace();
            }
        });
        try{
            sseEmitter.send(SseEmitter.event().reconnectTime(5000));
        }catch (IOException e){
            e.printStackTrace();
        }
        sseEmitterMap.put(uid,sseEmitter);
        log.info("[{}]创建sse连接成功!",uid);
        return sseEmitter;
    }

    public boolean sendMessage(String uid,String messageId,String message){
        if(StringUtils.isEmpty(message)){
            log.info("[{}]参数异常,msg为空",uid);
            return false;
        }
        SseEmitter sseEmitter = sseEmitterMap.get(uid);
        if(sseEmitter == null){
            log.info("[{}]sse连接不存在",uid);
            return  false;
        }
        try{
            sseEmitter.send(SseEmitter.event().id(messageId).reconnectTime(60000).data(message));
            log.info("用户{},消息ID:{},推送成功:{}",uid,messageId,message);
            return true;
        }catch (IOException e){
            sseEmitterMap.remove(uid);
            log.info("用户{},消息ID:{},消息推送失败:{}",uid,messageId,message);
            sseEmitter.complete();
            return false;
        }
    }

    public void closeSse(String uid){
        if(sseEmitterMap.containsKey(uid)){
            SseEmitter sseEmitter = sseEmitterMap.get(uid);
            sseEmitter.complete();
            sseEmitterMap.remove(uid);
        }else {
            log.info("用户{}连接已关闭",uid);
        }
    }

}

2、编写对应的Controller来实现具体业务

package com.test.controller;

import cn.hutool.core.util.IdUtil;
import com.test.service.SSEService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

@Controller
@RequestMapping("test")
public class TestController {
    @Autowired
    private SSEService sseService;
    @GetMapping("createSse")
    @CrossOrigin
    public SseEmitter createSse(String uid)
    {
        return sseService.crateSse(uid);
    }

    @GetMapping("sendMsg")
    @ResponseBody
    @CrossOrigin
    public String sseChat(String uid){
        for (int i = 0; i < 10; i++) {
            sseService.sendMessage(uid,"消息"+i,IdUtil.fastUUID().replace("-",""));
        }
        return "OK";
    }
    @GetMapping("closeSse")
    @CrossOrigin
    public void closeSse(String uid){
        sseService.closeSse(uid);
    }
}

三、前端实现消息的监听

<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>SSE消息推送监听</title>
</head>
<body>
    <div id="conMsg"></div>
<script>
    let uid = 1;
    let chat = document.getElementById("conMsg");
    if(window.EventSource){
        var eventSource = new EventSource(`http://127.0.0.1:8090/test/createSse?uid=${uid}`);
        eventSource.onopen = ()=>{
            console.log("链接成功");
        }
        eventSource.onmessage = (ev)=>{
            if(ev.data){
                chat.innerHTML += ev.data+"<br>";
            }
        }
        eventSource.onerror = ()=>{
            console.log("sse链接失败")
        }
    }else{
        alert("当前浏览器不支持sse")
    }
</script>
</body>
</html>

 

posted on 2024-11-04 15:25  铁猛  阅读(598)  评论(1编辑  收藏  举报

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