SSE技术，即Server Send Event与异步Servlet 3.0+、Websocket等为服务器端推送技术。SSE技术的特点是使用Http协议，轻量级易使用，在服务器端只要通过ContentType=“text/event-stream; charset=UTF-8”标明支持SSE即可，客户端也只需要建立请求到服务器端url的EventSource，再在EventSource上注册EventListener。相比之下，WebSocket采用的TCP/IP协议，设置较为复杂。
SSE示例：
1. 服务器端的Controller
package com.controller;
import java.util.Random;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class SseController {
/**
* "text/event-stream; charset=UTF-8"表明支持SSE这一服务器端推送技术，
* 字段后面部分"charset=UTF-8"必不可少，否则无法支持SSE。
* 服务器端发送的数据是连续的Stream，而不是一个数据包，
* 因此浏览器接收到数据后，不会关闭连接。
*
* @return 服务端向浏览器推送的消息，具有一定的格式要求，详见SSE说明
*/
@RequestMapping(value = "/push", produces = "text/event-stream; charset=UTF-8")
public @ResponseBody String push() {
Random random = new Random();
try {
Thread.sleep(5000);
} catch (InterruptedException ex) {
ex.printStackTrace();
}
return "data:This is a test data " + random.nextInt() + "\n\n"; // SSE 要求的数据格式，详见SSE说明
}
}2. 浏览器端(jsp)用EventSource作为客户端
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>SSE Demo</title>
</head>
<body>
<div id="msgDiv">This is a sse test</div>
<script type="text/javascript" src="assets/js/jquery-3.3.1.min.js"></script>
<script type="text/javascript">
if (!!window.EventSource) {
var source = new EventSource('push');
console.log(source.readyState);
s = ' ';
/* message event listener */
source.addEventListener('message', function(e) {
s += e.data + "<br/>";
$("#msgDiv").html(s);
});
/* open event listener */
source.addEventListener('open', function(e) {
console.log("Connection is open");
}, false);
/* error event listener */
source.addEventListener('error', function(e) {
if (e.readyState == EventSource.CLOSED) {
console.log("Connection is closed");
} else {
console.log("e.readyState");
}
}, false);
} else {
console.log("Your web browser dosen't support EventSource.");
}
</script>
</body>
</html>3. 测试结果
浏览器显示：
This is a test data -79652348
This is a test data -1095646155
This is a test data -1057602112
This is a test data -136222957
This is a test data 1348517168