JavaWeb 使用Filter实现用户自动登录（教材学习笔记）

1.编写User类

package cn.itcast.chapter08.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;
	}
}

2.实现登录页面

<%@ 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>

3.实现主页面

inde.jsp代码如下：

<%@ 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>

4、在cn.itcast.chapter08.filter包中创建LoginServlet类

代码如下：

package cn.itcast.chapter08.filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
import cn.itcast.chapter08.entity.User;
public class LoginServlet extends HttpServlet {
	public 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);
			// 发送自动登录的cookie
			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);
		}
	}
	public void doPost(HttpServletRequest request, 
          HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

5、编写LogoutServlet类，

代码如下：

package cn.itcast.chapter08.filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class LogoutServlet extends HttpServlet {
	public 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"); 
	}
	public void doPost(HttpServletRequest request,
         HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}
}

6、创建过滤器

AutoLoginFilter类代码如下：

package cn.itcast.chapter08.filter;
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
import cn.itcast.chapter08.entity.User;
public class AutoLoginFilter implements Filter {
	public void init(FilterConfig filterConfig) throws ServletException {
	}
	public void doFilter(ServletRequest req, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		// 获得一个名为 autologin 的cookie
		Cookie[] cookies = request.getCookies();
		String autologin = null;
		for (int i = 0; cookies != null && i < cookies.length; i++) {
			if ("autologin".equals(cookies[i].getName())) {
				// 找到了指定的cookie
				autologin = cookies[i].getValue();
				break;
			}
		}
		if (autologin != null) {
			// 做自动登录
			String[] parts = autologin.split("-");
			String username = parts[0];
			String password = parts[1];
			// 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);
			}
		}
		// 放行
		chain.doFilter(request, response);
	}
	public void destroy() {
	}
}

7、在web.xml中配置相关的几个servlet以及filter文件

代码如下：

<filter>
    <filter-name>AutoLoginFilter</filter-name>
    <filter-class>cn.itcast.chapter08.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>cn.itcast.chapter08.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>cn.itcast.chapter08.filter.LogoutServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LogoutServlet</servlet-name>
    <url-pattern>/LogoutServlet</url-pattern>
  </servlet-mapping>