jsp 实际上也是是一个继承自 Servlet 接口的 java 类，实际上它就是一个Servlet，JSP的页面渲染是在后端完成的，经过 tomcat 的处理后，把jsp转为 html 后，再统一发送给前端（浏览器）显示出来.

token实现单点登录

 <%@ page language="java" import="java.util.*,java.text.*" contentType="text/html;  charset =UTF-8" pageEncoding=" utf -8"%>
<%@page import="java.io.*" %>
<%@page import="java.net.*" %>
<%@page import="com.alibaba.fastjson.JSONObject"%>



<%
String ticket = transport("#34;,"username=xxxx&password=xxxx&service=#34;);
response.send Redirect ("#34;+ticket);
%>
<%!
public String transport(String url, String message) {
 StringBuffer  sb = new StringBuffer();
String ticket = "";
try {
URL urls = new URL(url);
HttpURLConnection uc = (HttpURLConnection) urls.openConnection();
uc.set Request Method("POST");
uc.setRequestProperty("content-type","application/x-www-form-urlencoded");
uc.setRequestProperty("charset", " UTF-8 ");
uc.setDoOutput(true);
uc.setDoInput(true);
uc.setReadTimeout(10000);
uc.setConnectTimeout(10000);
OutputStream os = uc.getOutputStream();
DataOutputStream dos = new DataOutputStream(os);
dos.write(message.getBytes("utf-8"));
dos.flush();
os.close();
BufferedReader in = new BufferedReader(new  InputStream Reader(uc.getInputStream(), "utf-8"));
String readLine = "";
while ((readLine = in.readLine()) != null) {
sb.append(readLine);
}
in.close();
//JSONObject json = JSONObject.fromObject(sb.toString());
//JSONObject data = JSONObject.fromObject(json.getString("data"));
JSONObject json = JSONObject.parseObject(sb.toString());
JSONObject data = JSONObject.parseObject(json.getString("data"));

ticket = data.get("ticket").toString();
System.out.println("ticket="+ticket);
} catch ( Exception  e) {
e.printStackTrace();
}
return ticket;
}
%>