javaweb会话技术

cookie的入门使用

package com.hspedu.cookie;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 演示如何创建cookie,并保存到浏览器
 */
public class CreateCookie extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CreateCookie 被调用...");


        //1. 创建一个Cookie对象
        //老韩解读
        //1) username 该cookie的名字 是唯一, 可以理解成是key
        //2) hsp : 该cookie的值
        //3) 可以创建多个cookie，老师就创建了一个
        //4) 这是cookie在服务器端, 还没有到浏览器
        Cookie cookie = new Cookie("username", "tom");
        Cookie cookie2 = new Cookie("email", "[email protected]");

        response.setContentType("text/html;charset=utf-8");
        //2. 将cookie发送给浏览器, 让浏览器将该cookie保存
        response.addCookie(cookie);
        response.addCookie(cookie2);

        PrintWriter writer = response.getWriter();
        writer.println("
创建cookie成功~
");
        writer.flush();
        writer.close();


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

修改cookie

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class UpdateCookie extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("UpdateCookie 被调用...");

        //需求
        /**
         * 1. 需求 演示如何修改Cookie
         * 1) 给定一个cookie的name, 找到该cookie, 如果找到, 则修改该cookie的值为 hsp-hi
         * 2) 如果找不到指定的cookie , 则提示, 没有该cookie
         */
        //1. 根据name 去查找 cookie
        String cookieName = "emailx";
        Cookie[] cookies = request.getCookies();

        //如果我们直接创建了一个同名的cookie
        Cookie userNameCookie = new Cookie("username", "hahaha");


        Cookie cookie = CookieUtils.readCookieByName(cookieName, cookies);
        if (null == cookie) {//在该浏览器没有email cookie
            System.out.println("当前访问 服务端的 浏览器没有 该cookie");
        } else {
            cookie.setValue("hsp-hi");
        }
        System.out.println("=====修改后的cookies信息=======");
        //2. 编写cookie
        for (Cookie cookie1 : cookies) {
            System.out.println("cookie name= " + cookie1.getName()
                    + " value= " + cookie1.getValue());
        }

        //3. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        //4. 如果希望我们的浏览器本地的cookie也修改，则需要使用response.addCookie(cookie);
        if(cookie != null) {
            response.addCookie(cookie);
        }
        //把 新创建的userNameCookie 重新保存到浏览器
        //如果 保存的userNameCookie 和已经有的cookie同名，就等价于替换.
        if(userNameCookie != null) {
            response.addCookie(userNameCookie);
        }
        PrintWriter writer = response.getWriter();
        writer.println("
完成修改cookie的任务..
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

读取cookie

package com.jxb.cooki;

import javax.servlet.http.Cookie;

public class CookieUtils {

    //编写一个方法，返回指定名字的cookie值
    public static Cookie readCookieByName(String name, Cookie[] cookies) {

        //判断传入的参数是否正确
        if (name == null || "".equals(name) || cookies == null || cookies.length == 0) {
            return null;
        }
        //遍历cookies
        for (Cookie cookie : cookies) {
            if(name.equals(cookie.getName())) {
                return cookie;
            }
        }
        return null;
    }
}

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class ReadCookieByNameServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("ReadCookieByNameServlet 被调用..");

        //得到指定的cookie的value
        //1. 先得到浏览器携带的所有cookie
        Cookie[] cookies = request.getCookies();
        //2. 使用工具类来获取指定的cookie
        Cookie emailCookie = CookieUtils.readCookieByName("username", cookies);
        if(null != emailCookie) {
            System.out.println("得到cookie name=" + emailCookie.getName()
                    + " value= " + emailCookie.getValue());
        } else {
            System.out.println("sorry, 没有这个cookie");
        }

        //3. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
完成读取cookie的任务..
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

/**
 * 读取从浏览器发送来的cookie信息[底层仍然是http协议]
 */
public class ReadCookies extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("ReadCookies 被调用..");


        //1. 通过request对象读取cookie信息
        Cookie[] cookies = request.getCookies();
        //2. 遍历cookie
        if (cookies != null && cookies.length != 0) {
            for (Cookie cookie : cookies) {
                System.out.println("cookie name= " + cookie.getName()
                        + " value= " + cookie.getValue());
            }
        }



        //3. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
读取cookie信息成功~
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

删除cookie

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class CookieLive extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CookieLive 被调用...");

        //演示创建一个cookie , 生命周期为 60s
        Cookie cookie = new Cookie("job", "java");
        //老韩解读:
        // 1. 从创建该cookie开始计时, 60秒后无效
        // 2. 浏览器来根据创建的时间，计时到60s秒，就认为该cookie无效
        // 3. 如果该cookie无效，那么浏览器在发出http请求时，就不在携带该cookie
        cookie.setMaxAge(60);
        //讲cookie保存到浏览器
        response.addCookie(cookie);


        //演示如何删除一个cookie, 比如删除username
        //1 先得到username cookie
        Cookie[] cookies = request.getCookies();
        Cookie usernameCookie =
                CookieUtils.readCookieByName("username", cookies);
        if(usernameCookie != null) {
            //2. 将其生命周期设置为0
            usernameCookie.setMaxAge(0);
            //3. 重新保存该cookie, 因为你将其生命周期设置0, 就等价于让浏览器删除该cookie
            //4. 说明：该cookie会被浏览器直接删除
            //   返回一个Set-Cookie: xxxxx => 一会抓包.
            //   Set-Cookie: username=tom; Expires=Thu, 01-Jan-1970 00:00:10 GMT
            response.addCookie(usernameCookie);//返回一个Set-Cookie: xxxxx => 一会抓包.
        }else{
            System.out.println("没有找到该cookie, 无法删除...");
        }

        /***********************
         * 默认的会话级别的 Cookie [即浏览器关闭就销毁了]
         * 前面我们讲课时，都是默认会话级别的生命周期
         ***********************/
        Cookie cookie3 = new Cookie("dkey", "dkey_value");
        /**
         * 老韩解读 setMaxAge源码
         * public void setMaxAge(int expiry) {
         *         this.maxAge = expiry;
         * }
         * private int maxAge = -1; 默认就是-1
         */
        //cookie.setMaxAge(-1);//设置存活时间
        response.addCookie(cookie3);


        // 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
设置cookie生命周期
");
        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

cookie路径

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class CookiePath extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CookiePath 被调用...");
        //1. 创建两个cookie
        Cookie cookie = new Cookie("address", "bj");
        Cookie cookie2 = new Cookie("salary", "20000");
        //2. 设置不同有效路径
        //   request.getContextPath() => /cs
        cookie.setPath(request.getContextPath());
        //   cookie2有效路径 /cs/aaa
        cookie2.setPath(request.getContextPath() + "/aaa");

        //老师说明：如果我们没有设置cookie有效路径，默认就是 /工程路径

        //3. 保存到浏览器
        response.addCookie(cookie);
        response.addCookie(cookie2);

        //4. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
设置cookie有效路径成功
");
        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

自动保存登陆名

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class UserUIServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("UserUIServlet .. 被调用..");
        //String contextPath = request.getContextPath();

        //老韩解读
        //1. 难度没有增加，-》文件多了 => 基础
        //2. 读取从浏览器发送来的cookie
        Cookie[] cookies = request.getCookies();
        Cookie loginuserCookie = CookieUtils.readCookieByName("loginuser", cookies);
        String username = "";
        if (loginuserCookie != null) {//如果有
            username = loginuserCookie.getValue();
        }

        response.setContentType("text/html;charset=utf-8");
        //1. 得到writer
        PrintWriter writer = response.getWriter();
        writer.println("\n" +
                "\n" +
                "\n" +
                "    \n" +
                "    \n" +
                "\n" +
                "\n" +
                "
用户登录界面
\n" +
                "
\n" +
                "    u: + username + "\" name=\"username\">
\n" +
                "    p:
\n" +
                "    \n" +
                "\n" +
                "\n" +
                "");


        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("LoginServlet 被调用...~~~");

        //1. 接收表单提交用户名和密码
        String username = request.getParameter("username");
        String pwd = request.getParameter("pwd");

        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        //2. 判断是否合法
        if ("hspedu".equals(username) && "123456".equals(pwd)) {
            //将登录成功的用户名，以cookie的形式，保存到浏览器
            Cookie loginuserCookie = new Cookie("loginuser", username);
            //设置该cookie生命周期
            loginuserCookie.setMaxAge(3600 * 24 * 3);
            response.addCookie(loginuserCookie);
            //合法
            writer.println("
登录OK
");

        } else {
            //不合法
            writer.println("
登录失败
");
        }

        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

cookie中文的解码与编码

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLEncoder;

public class EncoderCookie extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("EncoderCookie 被调用");
        //1. 创建cookie, 有中文
        //老韩解读
        //1) 如果直接存放中文的cookie, 报错 Control character in cookie value or attribute.
        //2) 解决方法，就是将中文 编程成 URL编码  英文： Encode=编码
        //3) 编码后，再保存即可
        String company = URLEncoder.encode("韩顺平教育", "utf-8");

        Cookie cookie = new Cookie("company", company);
        //2. 保存到浏览器
        response.addCookie(cookie);

        //3. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
设置中文cookie成功
");
        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

package com.jxb.cooki;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.URLDecoder;

public class ReadCookie2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        System.out.println("ReadCookie2 被调用..");
        //读取到中文cookie
        Cookie[] cookies = request.getCookies();
        Cookie companyCookie = CookieUtils.readCookieByName("company",cookies);
        String companyVal = companyCookie.getValue();
        System.out.println("companyVal= " + companyVal);//URL

        //解码
        companyVal = URLDecoder.decode(companyVal, "utf-8");
        System.out.println("解码后 companyVal= " + companyVal);//中文

        //3. 给浏览器返回信息
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
读取中文cookie解码成功~
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request,response);
    }
}

创建session

package com.jxb.cooki.session;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

public class CreateSession extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("CreateSession 被调用...");

        //1. 获取session, 同时也可能创建session
        HttpSession session = request.getSession();

        //2. 给session获取id
        System.out.println("CreateSession 当前sessionid= " + session.getId());
        //3. 给session存放数据
        session.setAttribute("email", "[email protected]");

        //4. 给浏览器发送一个回复
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
创建/操作session成功...
");
        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

读取session

package com.jxb.cooki.session;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

public class ReadSession extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("ReadSession 被调用...");
        // 演示读取session
        //1. 获取session, 如果没有sesion, 也会创建
        HttpSession session = request.getSession();
        //输出sessionId
        System.out.println("ReadSession sessionid= " + session.getId());
        //2. 读取属性
        Object email = session.getAttribute("email");
        if (email != null) {
            System.out.println("session属性 email= " + (String) email);
        } else {
            System.out.println("session中没有 email属性 ");
        }
        //给浏览器回复一下
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
读取session成功...
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

删除session

package com.jxb.cooki.session;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

public class DeleteSession extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("DeleteSession 被调用...");

        //演示如何删除session
        HttpSession session = request.getSession();
        session.invalidate();

        //老韩再多说一句, 如果你要删除session的某个属性
        //session.removeAttribute("xxx");

        //回复一下浏览器
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
删除session成功
");
        writer.flush();
        writer.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

session生命周期

package com.jxb.cooki.session;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

public class CreateSession2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("CreateSession2 被调用");
        //创建session
        HttpSession session = request.getSession();
        System.out.println("CreateSession2 sid= " + session.getId());
        //设置生命周期为 60s
        session.setMaxInactiveInterval(60);
        session.setAttribute("u", "jack");

        //回复一下浏览器
        response.setContentType("text/html;charset=utf-8");
        PrintWriter writer = response.getWriter();
        writer.println("
创建session成功, 设置生命周期60s
");
        writer.flush();
        writer.close();

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

package com.jxb.cooki.session;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class ReadSession2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //System.out.println("ReadSession2 被调用...");

        //1. 获取到session
        HttpSession session = request.getSession();
        System.out.println("ReadSession2 sid= " + session.getId());
        //2. 读取session的属性
        Object u = session.getAttribute("u");
        if (u != null) {
            System.out.println("读取到session属性 u= " + (String) u);
        } else {
            System.out.println("读取不到session属性 u 说明原来的session被销毁");
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

CreateSession 当前sessionid= AC78607B4FCC8DC93DE3B3960CE247E7
ReadSession sessionid= AC78607B4FCC8DC93DE3B3960CE247E7
session属性 email= zs@qq.com
DeleteSession 被调用...
ReadSession sessionid= 9465084646BE295082D77AB68F44F7CE
session中没有 email属性 
CreateCookie 被调用...
CreateSession2 被调用
CreateSession2 sid= 9465084646BE295082D77AB68F44F7CE
ReadSession2 sid= 9465084646BE295082D77AB68F44F7CE
读取到session属性 u= jack

session作业

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>登录失败</title>
</head>
<body>
<h1>登录失败</h1>
<!--
老韩回顾 web工程路径专题
1. a 标签是 浏览器解析
2. 第一 / 被解析成 http://localhost:8080/
3. 如果没有 / 会以当前浏览器地址栏 的 http://localhost:8080/工程路径../资源 去掉资源部分作为参考路径
4  其它的回顾请大家看 web工程路径专题~~ , 他会贯彻 整个java后端开发
-->
<a href="/cooki/userlogin.html">点击重新登录</a>
</body>
</html>

package com.jxb.cooki.session.homework;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

public class LoginCheckServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("LoginCheckServlet 被调用..");
        //功能-> 自己拆解 -> 逐步实现 [大量练习]
        //1. 得到提交的用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        if("666666".equals(password)) {//认为合法
            //把用户名保存到 session
            HttpSession session = request.getSession();
            session.setAttribute("loginuser", username);

            //请求转发到ManageServlet
            request.getRequestDispatcher("/manage").forward(request, response);
        } else {
            //请求转发进入到 error.html
            request.getRequestDispatcher("/error.html").forward(request, response);
        }


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}

package com.jxb.cooki.session.homework;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;

public class ManageServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //判断该用户是否登录过
        HttpSession session = request.getSession();
        Object loginuser = session.getAttribute("loginuser");
        if(loginuser == null) {//说明该用户没有登录
            //重新登录-> 请求重定向
            //response.sendRedirect("/cs/userlogin.html");
            response.sendRedirect(request.getContextPath() + "/userlogin.html");
            return;
        } else {
            response.setContentType("text/html;charset=utf-8");
            PrintWriter writer = response.getWriter();
            writer.println("
用户管理页面
");
            writer.println("欢迎你, 管理员：" + loginuser.toString());
            writer.flush();
            writer.close();
        }
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doPost(request, response);
    }
}