Cookie实现用户自动登录

UseController类添加新方法

    /**
     * 用户登录方法
     * @param req
     * @param resp
     * @throws ServletException
     * @throws IOException
     */
    @SuppressWarnings("unused")
    private void login(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String expiredays = req.getParameter("expiredays");
        Cookie[] cookies = req.getCookies();
        //是否登陆的标记，true登录false未登录
        boolean login = false;
        String account = null;//登录账号
        String ssid = null;//这是一个标记，通过cookie判断一个用户该不该成功登录
        /**
         * 非首次登陆，获取userKey和ssid对应的值
         */
        if(cookies != null && cookies.length > 0) {
            for (Cookie cookie : cookies) {
                if(cookie.getName().equals("userKey")) {
                    account = cookie.getValue();
                }

                if(cookie.getName().equals("ssid")) {
                    ssid = cookie.getValue();
                }
            }
        }

        if(account != null && ssid != null) {
            login = ssid.equals(CookiesUtils.md5Encrypt(username));
        }

        if(!login) {//用户首次登陆，不实用Cookie
            //第一次登录
            User user = userService.login(username, password);//通过访问数据库检查用户名和密码
            //登录成功返回用户，登录失败返回null
            if(user != null) { //首次登陆成功
                //写cookie
                expiredays = (expiredays==null)?"":expiredays;
                /**
                 * 写入相关的cookie,分别为userKey和ssid对应的信息
                 */
                switch (expiredays) {
                case "7" : {
                    CookiesUtils.createCookie(username, req, resp, 7*24*60*60);
                    break;
                }
                case "30" : {
                    //创建cookie 30天
                    CookiesUtils.createCookie(username, req, resp, 30*24*60*60);
                    break;
                }
                case "100" : {
                    //创建cookie 永远 Integer.Max
                    CookiesUtils.createCookie(username, req, resp, Integer.MAX_VALUE);
                    break;
                }
                default : {
                    CookiesUtils.createCookie(username, req, resp, -1);
                    break;
                }
                }
                //登陆成功
                req.getRequestDispatcher("/main.jsp").forward(req, resp);
            }else {//首次登陆用户名或密码错误
                req.setAttribute("note", "用户名或密码是错误的！");
                req.getRequestDispatcher("/login.jsp").forward(req, resp);
            }
        } else {//Cookie登陆成功
            expiredays = (expiredays==null)?"":expiredays;
            if(expiredays.equals("-1")) {
                CookiesUtils.createCookie(username, req, resp, -1);
            }
            req.getRequestDispatcher("/main.jsp").forward(req, resp);
        }

    }

1，注意表单提交的名字，一定是login.udo才能被此函数执行
2，程序正常执行需要CookiesUtils工具

CookiesUtils工具

package com.foot.mvcpro.utils;

import java.security.MessageDigest;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public final class CookiesUtils {
    private static final String KEY = "cookie key";
    /**
     * 指令浏览器创建cookie的方法
     * @param username 放到cookie的用户名
     * @param req
     * @param resp 调用addcookie方法的response对象
     * @param sec 失效时间 单位：秒
     */
    public static void createCookie(String username, HttpServletRequest req, HttpServletResponse resp, int sec) {
        //写入userKey和ssid信息，方便下次登陆查询
        Cookie userCookie = new Cookie("userKey", username);
        Cookie ssidCookie = new Cookie("ssid", md5Encrypt(username));
        userCookie.setMaxAge(sec);
        ssidCookie.setMaxAge(sec);
        resp.addCookie(userCookie);
        resp.addCookie(ssidCookie);
    }
    /**
     * 把一个明文字符串加密成密文
     * @param str 要加密的明文
     * @return
     */
    public static String md5Encrypt(String str) {
        str= (str==null)?"":(str+KEY);
        char[] md5Digst = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};//字典
        try {
            MessageDigest md = MessageDigest.getInstance("MD5");//MD5  sha1
            byte[] strArr = str.getBytes();
            md.update(strArr);//把明文放到MessageDigest的对象中，更新数据
            byte[] msg = md.digest();//加密操作
            //进一步加密
            int len = msg.length;

            char[] result = new char[len*2];
            int k = 0;

            for(int i = 0; i < len; i++) {
                byte b = msg[i];
                result[k++] = md5Digst[b>>4 & 0xf];
                result[k++] = md5Digst[b & 0xf];
            }
            System.out.println(result);
            return new String(result);

        } catch(Exception e) {
            e.printStackTrace();
        }
        return null;
    }
 }

jsp页面

<%@ 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>永久登录</title>

<script type="text/javascript">
/****如果以下代码出现有错误，需参考[JavaWeb内javascript出错检测方法](https://blog.csdn.net/footprint01/article/details/82463938)的方法来纠错*****/
    /**
     * 获取指定的键值对对应键的值
     */
    function getCookie(c_name) {
        if(document.cookie.length > 0) {
            var c_start = document.cookie.indexOf(c_name+"=");
            c_start = c_start + c_name.length + 1;
            var c_end = document.cookie.indexOf(";", c_start);
            if(c_end == -1) {
                c_end = document.cookie.length;
            }
            return unescape(document.cookie.substring(c_start, c_end));
        }
    }

    //
    window.onload=function(){
        //alert(123456);
        var form = document.getElementById("loginform");
        var username = document.getElementById("username");
        var password = document.getElementById("password");
        if(getCookie("userKey") != null && getCookie("userKey") != "" && getCookie("ssid") != null && getCookie("ssid") != "") {
            username.value = getCookie("userKey");
            password.value = getCookie("ssid");
            //form.submit();//设置自动提交
        }
    }
</script>

</head>
<body>

    <br><br>
        <% if(request.getAttribute("note") != null) { %>
        <span style="color: red; font-weight: bolder;"><%=request.getAttribute("note") %></span>
        <% } %>
    <br><br>

    <form id="loginform" action="<%=request.getContextPath()%>/login.udo" method="get">
        用户名：<input id="username" type="text" name="username" value=""/> 
        <br> <br> 
        密 码：<input id="password" type="text" name="password" value=""/> 
        <br> <br> 
            <input type="radio" name="expiredays" value="7" /> 记住我一周
            <input type="radio" name="expiredays" value="30" /> 记住我一个月
            <input type="radio" name="expiredays" value="100" /> 永远记住
            <input type="radio" name="expiredays" value="-1" /> 忘掉密码
         <br> <br> 
        <input type="submit" value="登录" />
    </form>

</body>
</html>

username.value = getCookie(“userKey”);
password.value = getCookie(“ssid”);//使建立的网页内哟内容
//form.submit();//设置自动提交该代码可以实现自动提交。