利用session完成用户登陆

 package cn.itcast.cookie;

 import java.io.IOException;
 import java.io.PrintWriter;
 import java.util.List;

 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 javax.servlet.http.HttpSession;

 import cn.itcast.Db;
 import cn.itcast.Db1;
 import cn.itcast.User;

 public class SessionDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setCharacterEncoding("UTF-8");
         response.setContentType("text/html;charset=UTF-8");
         PrintWriter out = response.getWriter();

         String username = request.getParameter("username");
         String password = request.getParameter("password");

         List<User> list = Db1.getAll();
         for (User user : list) {
             if(user.getUsername().equals(username)&&user.getPassword().equals(password)){
                 request.getSession().setAttribute("user", user);//登录成功，向session存入一个登录标记
                 response.sendRedirect("/ServletDemo/index.jsp");
                 return;
             }
         }

         out.write("用户名或密码错误！");
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

 }

 package cn.itcast.cookie;

 import java.io.IOException;
 import java.io.PrintWriter;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpSession;

 //完成任务注销
 public class SessionDemo2 extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setCharacterEncoding("UTF-8");
         response.setContentType("text/html;charset=UTF-8");
         PrintWriter out = response.getWriter();

         HttpSession session = request.getSession();
         if(session==null){
             response.sendRedirect("/ServletDemo/index.jsp");
             return;
         }

         session.removeAttribute("user");
         response.sendRedirect("/ServletDemo/index.jsp");

     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

     }

 }

 package cn.itcast;

 import java.util.ArrayList;
 import java.util.List;

 public class Db1 {

     public static List list = new ArrayList();
     static{
         list.add(new User("aaa","123"));
         list.add(new User("bbb","123"));
         list.add(new User("ccc","123"));
         list.add(new User("ddd","123"));
     }

     public static List getAll(){
         return list;
     }

 }

 package cn.itcast;

 public class User {
     private String username;

     public User() {
         super();
     }

     public User(String username, String password) {
         super();
         this.username = username;
         this.password = password;
     }

     private String password;

     public String getUsername() {
         return username;
     }

     public void setUsername(String username) {
         this.username = username;
     }

     public String getPassword() {
         return password;
     }

     public void setPassword(String password) {
         this.password = password;
     }

 }

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 <%
 String path = request.getContextPath();
 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 %>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
   <head>
     <base href="<%=basePath%>">

     <title>My JSP 'index.jsp' starting page</title>
     <meta http-equiv="pragma" content="no-cache">
     <meta http-equiv="cache-control" content="no-cache">
     <meta http-equiv="expires" content="0">
     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
     <meta http-equiv="description" content="This is my page">
     <!--
     <link rel="stylesheet" type="text/css" href="styles.css">
     -->
   </head>

   <body>
     欢迎您：${user.username }<a href="/ServletDemo/register.html">登录</a> <a href="/ServletDemo/servlet/SessionDemo2">退出登录</a>
   </body>
 </html>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 <html>
     <head>
         <title>register.html</title>

     </head>

     <style>
     </style>

     <body>
         <form action="/ServletDemo/servlet/SessionDemo" method="get">
         用户名：
         <input type="text" name="username">
         <br />
         密码：
         <input type="password" name="password">
         <br />
         <input type="submit" value="注册" />
         </form>
     </body>
 </html>