实验名称：

使用Filter实现用户登录

实验目的：

（1）了解什么是Filter。

（2）熟悉Filter的拦截过程和接口中的方法。

（3）掌握第一个Filter程序的编写方法。

（4）能够使用Filter实现用户自动登录

实验内容及原理：

通过前面的学习，我们已经了解到，使用Cookie可以实现用户自动登录的功能。但是使用Cookie实现用户自动登录后，当客户端访问服务器的Servlet时，所有的Servlet都需要对用户的Cookie信息进行校验，这样势必会导致在Servlet程序中书写大量重复的代码。为了解决这种问题，可以在Filter程序中实现Cookie的校验。本实验使用Filter实现用户的自动登录功能。

实验设备及实验步骤：

Win10操作系统+JDK软件+Idea软件+Apache-tomcat软件

1、创建动态WEB项目（5分）

2、编写User类

package com.example.filter7.entity;
public class User {
    private String username;
    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;
    }
}

3、实现登录页面login.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
         pageEncoding="utf-8" import="java.util.*"%>
<html>
<head></head>
<center><h3>用户登录</h3></center>
<body style="text-align: center;">
<form action="${pageContext.request.contextPath }/LoginServlet"
      method="post">
    <table border="1" width="600px" cellpadding="0" cellspacing="0"
           align="center" >
        <tr>
            <td height="30" align="center">用户名：</td>
            <td>&nbsp;&nbsp;
                <input type="text" name="username" />${errerMsg }</td>
        </tr>
        <tr>
            <td height="30" align="center">密   &nbsp; 码：</td>
            <td>&nbsp;&nbsp;
                <input type="password" name="password" /></td>
        </tr>
        <tr>
            <td height="35" align="center">自动登录时间</td>
            <td><input type="radio" name="autologin"
                       value="${60*60*24*31 }" />一个月
                <input type="radio" name="autologin"
                       value="${60*60*24*31*3 }" />三个月
                <input type="radio" name="autologin"
                       value="${60*60*24*31*6 }" />半年
                <input type="radio" name="autologin"
                       value="${60*60*24*31*12 }" />一年
            </td>
        </tr>
        <tr>
            <td height="30" colspan="2" align="center">
                <input type="submit" value="登录" />
                &nbsp;&nbsp;&nbsp;&nbsp;
                <input type="reset" value="重置" />
            </td>
        </tr>
    </table>
</form>
</body>
<html>

4、实现首页index.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
         pageEncoding="utf-8" import="java.util.*"
%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<html>
<head>
    <title>显示登录的用户信息</title>
</head>
<body>
<br />
<center>
    <h3>欢迎光临</h3>
</center>
<br />
<br />
<c:choose>
    <c:when test="${sessionScope.user==null }">
        <a href="${pageContext.request.contextPath }/login.jsp">用户登录</a>
    </c:when>
    <c:otherwise>
        欢迎你，${sessionScope.user.username }!
        <a href="${pageContext.request.contextPath }/LogoutServlet">注销</a>
    </c:otherwise>
</c:choose>
<hr />
</body>
</html>

5、编写LoginServlet类。

package com.example.filter7.filter;
//省略导包
@WebServlet(name = "LoginServlet")
public class LoginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 获得用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        // 检查用户名和密码
        if ("itcast".equals(username) && "123456".equals(password)) {
            // 登录成功
            // 将用户状态 user 对象存入 session域
            User user = new User();
            user.setUsername(username);
            user.setPassword(password);
            request.getSession().setAttribute("user", user);
            // 获取用户选择的自动登录有效时间
            String autoLogin = request.getParameter("autologin");
            if (autoLogin != null) {
                // 注意 cookie 中的密码要加密
                Cookie cookie = new Cookie("autologin", username + "-"
                        + password);
                cookie.setMaxAge(Integer.parseInt(autoLogin));
                cookie.setPath(request.getContextPath());
                response.addCookie(cookie);
            }
            // 跳转至首页
            response.sendRedirect(request.getContextPath() + "/index.jsp");
        } else {
            request.setAttribute("errerMsg", "用户名或密码错");
            request.getRequestDispatcher("/login.jsp")
                    .forward(request, response);
        }
    }
}

6、编写LogoutServlet类。

package com.example.filter7.filter;
//省略导包
@WebServlet(name = "LogoutServlet")
public class LogoutServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 用户注销
        request.getSession().removeAttribute("user");
        // 从客户端删除自动登录的cookie
        Cookie cookie = new Cookie("autologin", "msg");
        cookie.setPath(request.getContextPath());
        cookie.setMaxAge(0);
        response.addCookie(cookie);
        response.sendRedirect(request.getContextPath()+"/index.jsp");
    }
}

7、创建过滤器AutoLoginFilter类。

package com.example.filter7.filter;
//省略导包
@WebServlet(name = "LogoutServlet")
public class LogoutServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 用户注销
        request.getSession().removeAttribute("user");
        // 从客户端删除自动登录的cookie
        Cookie cookie = new Cookie("autologin", "msg");
        cookie.setPath(request.getContextPath());
        cookie.setMaxAge(0);
        response.addCookie(cookie);
        response.sendRedirect(request.getContextPath()+"/index.jsp");
    }
}

8、配置映射信息。

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    <filter>
        <filter-name>AutoLoginFilter</filter-name>
        <filter-class>com.example.filter7.filter.AutoLoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>AutoLoginFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.example.filter7.filter.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/LoginServlet</url-pattern>
    </servlet-mapping>

    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>com.example.filter7.filter.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/LogoutServlet</url-pattern>
    </servlet-mapping>
</web-app>