记住用户名的，选中复选框则记住用户名和密码，下次登录的时候就方便用户名的登陆

记住用户名的，选中复选框则记住用户名和密码，下次登录的时候就方便用户名的登陆：
package com.laizhi.util;

import java.io.IOException;

import java.io.PrintWriter;

import java.io.UnsupportedEncodingException;

import javax.servlet.FilterChain;

import javax.servlet.ServletException;

import javax.servlet.http.Cookie;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

import java.security.MessageDigest;

import java.security.NoSuchAlgorithmException;

import com.laizhi.bean.User;

import com.laizhi.dao.UserDAO;

import com.laizhi.factory.DaoImplFactory;

import com.sun.org.apache.xerces.internal.impl.dv.util.Base64;

/*

* 2014.07.01

* */

public class CookieUtil {
       //保存cookie时的cookieName
       private final static String cookieDomainName = “laizhi”;
       //加密cookie时的网站自定码

       private final static String webKey = “123456”;
       //设置cookie有效期是两个星期，根据需要自定义
       private final static long cookieMaxAge = 60 * 60 * 24 * 7 * 2;
       //保存Cookie到客户端-------------------------------------------------------------------------
       //在CheckLogonServlet.java中被调用
       //传递进来的user对象中封装了在登陆时填写的用户名与密码

       public static void saveCookie(User user, HttpServletResponse response) {
              //cookie的有效期
              long validTime = System.currentTimeMillis() + (cookieMaxAge * 5000);
              //MD5加密用户详细信息
              String cookieValueWithMd5 =getMD5(user.getUserName() + ":" + user.getPassword()

                            + ":" + validTime + ":" + webKey);
              //将要被保存的完整的Cookie值
              String cookieValue = user.getUserName() + ":" + validTime + ":" + cookieValueWithMd5;
              //再一次对Cookie的值进行BASE64编码

              String cookieValueBase64 = new String(Base64.encode(cookieValue.getBytes()));
              //开始保存Cookie
              Cookie cookie = new Cookie(cookieDomainName, cookieValueBase64);
              //存两年(这个值应该大于或等于validTime)
              cookie.setMaxAge(60 * 60 * 24 * 365 * 2);

              //cookie有效路径是网站根目录

              cookie.setPath("/");

              //向客户端写入

              response.addCookie(cookie);

       }

      

       //读取Cookie,自动完成登陆操作----------------------------------------------------------------

       //在Filter程序中调用该方法,见AutoLogonFilter.java

       public static void readCookieAndLogon(HttpServletRequest request, HttpServletResponse response,

FilterChain chain) throws IOException, ServletException,UnsupportedEncodingException{
       //根据cookieName取cookieValue
       Cookie cookies[] = request.getCookies();
                     String cookieValue = null;
                     if(cookies!=null){
                            for(int i=0;i
                                   if (cookieDomainName.equals(cookies[i].getName())) {
                                          cookieValue = cookies[i].getValue();
                                          break;
                                   }

                            }

                     }
                     //如果cookieValue为空,返回,
                     if(cookieValue==null){
                            return;
                     }
              //如果cookieValue不为空,才执行下面的代码
              //先得到的CookieValue进行Base64解码
              String cookieValueAfterDecode = new String (Base64.decode(cookieValue),"utf-8");
              //对解码后的值进行分拆,得到一个数组,如果数组长度不为3,就是非法登陆
              String cookieValues[] = cookieValueAfterDecode.split(":");
              if(cookieValues.length!=3){
                     response.setContentType("text/html;charset=utf-8");
                     PrintWriter out = response.getWriter();
                     out.println("你正在用非正常方式进入本站...");
                     out.close();
                     return;
              }
              //判断是否在有效期内,过期就删除Cookie
              long validTimeInCookie = new Long(cookieValues[1]);
              if(validTimeInCookie < System.currentTimeMillis()){
                     //删除Cookie
                     clearCookie(response);
                     response.setContentType("text/html;charset=utf-8");
                     PrintWriter out = response.getWriter();
                     out.println("");你的Cookie已经失效,请重新登陆
                     out.close();
                     return;
              }
              //取出cookie中的用户名,并到数据库中检查这个用户名,
              String username = cookieValues[0];
             
              //根据用户名到数据库中检查用户是否存在
              UserDAO ud = DaoImplFactory.getInstance();
              User user = ud.selectUserByUsername(username);

              //如果user返回不为空,就取出密码,使用用户名+密码+有效时间+ webSiteKey进行MD5加密
              if(user!=null){
                     String md5ValueInCookie = cookieValues[2];
                     String md5ValueFromUser =getMD5(user.getUserName() + ":" + user.getPassword()
                                   + ":" + validTimeInCookie + ":" + webKey);
                     //将结果与Cookie中的MD5码相比较,如果相同,写入Session,自动登陆成功,并继续用户请求
                     if(md5ValueFromUser.equals(md5ValueInCookie)){
                            HttpSession session = request.getSession(true);
                            session.setAttribute("user", user);
                            chain.doFilter(request, response);
                     }

              }else{

              //返回为空执行
                     response.setContentType("text/html;charset=utf-8");
                     PrintWriter out = response.getWriter();
                     out.println("cookie验证错误！");
                     out.close();
               return;

             }

       }

      

       //用户注销时,清除Cookie,在需要时可随时调用-----------------------------------------------------
       public static void clearCookie( HttpServletResponse response){
              Cookie cookie = new Cookie(cookieDomainName, null);
              cookie.setMaxAge(0);
              cookie.setPath("/");
              response.addCookie(cookie);
       }

//获取Cookie组合字符串的MD5码的字符串----------------------------------------------------------------
              public static String getMD5(String value) {
                     String result = null;
                     try{
                            byte[] valueByte = value.getBytes();
                            MessageDigest md = MessageDigest.getInstance("MD5");
                            md.update(valueByte);
                            result = toHex(md.digest());
                     } catch (NoSuchAlgorithmException e2){
                            e1.printStackTrace();
                     }
                     return result;
              }
      //将传递进来的字节数组转换成十六进制的字符串形式并返回
              private static String toHex(byte[] buffer){
                     StringBuffer sb = new StringBuffer(buffer.length * 2);
                     for (int i = 0; i < buffer.length; i++){
                            sb.append(Character.forDigit((buffer[i] & 0xf0) >> 4, 16));
                            sb.append(Character.forDigit(buffer[i] & 0x0f, 16));
                     }
                     return sb.toString();
              }
}