案例目标

情景：系统中的某些页面只有在正常登陆后在可以访问，用户请求这些页面是，需要先检查Session中有无该用户的信息，但是在所有必要的页面上加上对session的判断相当麻烦，因此利用filter实现对资源权限的统一管理

方案：编写一个检测使用户是否登录的过滤器，若未登录，则重定向到登录界面

要求：1.session中的键保存在配置文件中

2.如果用户未登录，则重定向到指定界面

3.未登录用户也可以访问的url列表已配置文件的方式保存

新建抽象类HttpFilter继承Filter类

package com.nupt.javaweb.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 javax.servlet.http.HttpServletResponse;

public abstract class HttpFilter implements Filter {

	private FilterConfig filterConfig;
	@Override
	public void init(FilterConfig filterConfig) throws ServletException {
		// TODO Auto-generated method stub
		this.filterConfig = filterConfig;
		init();

	}
	//Using the function to init Filter
	protected void init() {}
	public FilterConfig getFilterConfig() {
		return this.filterConfig;
	}
	@Override
	public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
			throws IOException, ServletException {
		// TODO Auto-generated method stub
		HttpServletRequest request = (HttpServletRequest)req;
		HttpServletResponse response = (HttpServletResponse)resp;
		doFilter( request ,response,chain);

	}
	public abstract void doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain chain) throws IOException, ServletException;

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}
}

新建a.jsp,b.jsp,c.jsp,d.jsp,e.jsp，list.jsp作为要访问的资源

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<h4>AAA</h4>
	<br/>
	<a href="<%= request.getContextPath() %>/login/list.jsp">Return......</a>
</body>
</html>

list.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<a href="<%= request.getContextPath()%>/login/a.jsp">AAA</a>
	<br/>
	<a href="<%= request.getContextPath()%>/login/b.jsp">BBB</a>
	<br/>
	<a href="<%= request.getContextPath()%>/login/c.jsp">CCC</a>
	<br/>
	<a href="<%= request.getContextPath()%>/login/d.jsp">DDD</a>
	<br/>
	<a href="<%= request.getContextPath()%>/login/e.jsp">EEE</a>
</body>
</html>

新建login.jsp与doLogin.jsp分别用于用户登录，与中间件servlet

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="doLogin.jsp" method="post">
		用户名:<input type="text" name="username"/>
		<br/>
		<input type="submit" value="登录" />
	</form>
</body>
</html>

doLogin.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<%
		String userSessionKey = application.getInitParameter("userSessionKey");
		String username = request.getParameter("username");
		if( username != null && !username.trim().equals("")){
			session.setAttribute(userSessionKey, username);
			response.sendRedirect(request.getContextPath()+"/login/list.jsp");
		}
	%>
</body>

修改配置文件web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="WebApp_ID" version="3.0">
	<!-- 用户信息放入到Session中的键的名字 -->
	<context-param>
		<param-name>userSessionKey</param-name>
		<param-value>USERSESSIONKEY</param-value>
	</context-param>
	<!-- 若未登录需要重定向的页面 -->
	<context-param>
		<param-name>redirectPage</param-name>
		<param-value>/login/login.jsp</param-value>
	</context-param>
	<!-- 不需要检查或者拦截的URL列表 -->
	<context-param>
		<param-name>unCheckedUrls</param-name>
		<param-value>/login/a.jsp,/login/list.jsp,/login/login.jsp,/login/doLogin.jsp</param-value>
	</context-param>
	<filter>
		<filter-name>loginFilter</filter-name>
		<filter-class>com.nupt.javaweb.login.LoginFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>loginFilter</filter-name>
		<url-pattern>/login/*</url-pattern>
	</filter-mapping>
</web-app>

新建LoginFilter类实现HttpFilter类

package com.nupt.javaweb.login;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.nupt.javaweb.filter.HttpFilter;

public class LoginFilter extends HttpFilter {
	
	
	FilterConfig filterConfig;
	ServletContext servletContext;
	String userSessionKey;
	String redirectPage;
	String unCheckedUrls;
	protected void init() {

//		获取用户信息放入到Session中的键值
		filterConfig = this.getFilterConfig();
		servletContext = filterConfig.getServletContext();
		userSessionKey = servletContext.getInitParameter("userSessionKey");
//		获取若用户未登录重定向的页面
		redirectPage = servletContext.getInitParameter("redirectPage");
//		获取无需拦截的url资源
		unCheckedUrls = servletContext.getInitParameter("unCheckedUrls");
	}
	@Override
	public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException  {
		// TODO Auto-generated method stub
		System.out.println("Hello Filter");
//		1.获取servletpath
		String servletPath = request.getServletPath();
//		2判断用户请求的资源是否可以不用登陆就可以访问
		if( this.unCheckedUrls.contains(servletPath)) {
			//System.out.println("servletPath.contains(unCheckedUrls)==true");
			chain.doFilter(request, response);
			return;
		}else{
//			判断HttpSession对象中有没有用户登录的属性信息
			HttpSession httpSession = request.getSession();
			String username = (String) httpSession.getAttribute(this.userSessionKey);
			if( username != null ) {
				chain.doFilter(request, response);
				return;
			}else
				try {
					response.sendRedirect(request.getContextPath()+this.redirectPage);
					return;
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
		}
	}

}

利用Filter与Session实现登录用户可以访问资源，未登录用户禁止访问