1 说明
我们给出三个页面：index.jsp、user.jsp、admin.jsp。
设计User类：username、password、grade，其中grade表示用户等级，1表示普通用户，2表示管理员用户。
当用户登录成功后，把user保存到session中。
创建LoginFilter，它有两种过滤方式：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<servlet>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.cug.web.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/LoginServlet</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<filter>
<filter-name>UserFilter</filter-name>
<filter-class>com.cug.filter.UserFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>UserFilter</filter-name>
<url-pattern>/user/*</url-pattern>
</filter-mapping>
<filter>
<filter-name>AdminFilter</filter-name>
<filter-class>com.cug.filter.AdminFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>AdminFilter</filter-name>
<url-pattern>/admin/*</url-pattern>
</filter-mapping>
</web-app>package com.cug.web.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.cug.domain.User;
import com.cug.web.service.UserService;
public class LoginServlet extends HttpServlet{
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
String username = req.getParameter("username");
String password = req.getParameter("password");
User user = UserService.login(username, password);
if(user == null){
req.setAttribute("msg", "用户名或者密码错误");
req.getRequestDispatcher("/login.jsp").forward(req, resp);
} else{
req.getSession().setAttribute("user", user);
req.getRequestDispatcher("index.jsp").forward(req,resp);
}
}
}
package com.cug.web.service;
import java.util.HashMap;
import java.util.Map;
import com.cug.domain.User;
public class UserService {
private static Map<String, User> users = new HashMap<String, User>();
static{
users.put("zhu", new User("zhu", "123", 2));
users.put("xiao", new User("xiao", "123", 1));
}
public static User login(String username, String password){
User user = users.get(username);
if(user == null)
return null;
if(!user.getPassword().equals(password))
return null;
return user;
}
}
package com.cug.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import com.cug.domain.User;
public class AdminFilter implements Filter{
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
req.setCharacterEncoding("utf-8");
resp.setContentType("text/html;charset=utf-8");
HttpServletRequest request = (HttpServletRequest)req;
User user = (User)request.getSession().getAttribute("user");
if(user == null){
resp.getWriter().print("用户还没有登陆");
request.getRequestDispatcher("/login.jsp").forward(req, resp);
}
if(user.getGrade() < 2){
resp.getWriter().print("您的等级不够");
return;
}
chain.doFilter(req, resp);
}
@Override
public void init(FilterConfig arg0) throws ServletException {
}
}
package com.cug.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import com.cug.domain.User;
public class UserFilter implements Filter{
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
HttpServletRequest httpReq = (HttpServletRequest)request;
User user = (User)httpReq.getSession().getAttribute("user");
if(user == null){
request.getRequestDispatcher("/login.jsp").forward(request, response);
}
chain.doFilter(request, response);
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
}
package com.cug.domain;
public class User {
private String username;
private String password;
private int grade;
public User() {
super();
}
public User(String username, String password, int grade) {
super();
this.username = username;
this.password = password;
this.grade = grade;
}
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;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}
@Override
public String toString() {
return "User [username=" + username + ", password=" + password
+ ", grade=" + grade + "]";
}
}
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%
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 'admin.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>
<h1>admin.jsp</h1>
<h3>${user.username }</h3>
<a href="<c:url value='/index.jsp'/>">首页</a><br/>
<a href="<c:url value='/user/user.jsp'/>">用户页</a><br/>
<a href="<c:url value='/admin/admin.jsp'/>">系统管理员</a><br/>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'user.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<h1>user.jsp</h1>
<h3>${user.username }</h3>
<a href="<c:url value='/index.jsp'/>">首页</a><br>
<a href="<c:url value='/user/user.jsp'/>">用户登陆界面</a><br>
<a href="<c:url value='/admin/admin.jsp'/>">管理员登陆界面</a><br>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%
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 'login.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>
${msg }
<form action="<c:url value='/LoginServlet'/>" method="post">
用户名：<input type="text" name="username"/><br/>
密码：<input type="password" name="password"/><br/>
<input type="submit" value="登陆"/>
</form>
</body>
</html>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<h1>index.jsp</h1>
<h3>${user.username }</h3>
<a href="<c:url value='/index.jsp'/>">首页</a><br>
<a href="<c:url value='/user/user.jsp'/>">用户登陆界面</a><br>
<a href="<c:url value='/admin/admin.jsp'/>">管理员登陆界面</a><br>
</body>
</html>
原文地址：http://blog.csdn.net/bluzelee2011/article/details/42784479
