filter应用案例二：权限控制

filter可以用来进行权限控制，比如admin文件夹下的文件只允许管理员进入，那么，可以给admin文件夹加上一个过滤器：

简单代码示例：

 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;
 public class RCFilter implements Filter {
     public void destroy() {}
     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
         HttpServletRequest req=(HttpServletRequest) request;
         String admin=(String) req.getSession().getAttribute("admin");    //查看管理员是否登录，这里只是用于演示，方便起见，用字符串代替管理员类
         if(admin==null)
         {
             System.out.println("您不是管理员，不得进入该页面！");    //管理员未登录，不放行
         }
         else chain.doFilter(request, response);            //放行
     }
     public void init(FilterConfig fConfig) throws ServletException {}
 }

RCFilter

 <?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
   <display-name></display-name>
   <welcome-file-list>
     <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
   <filter>
     <display-name>RCFilter</display-name>
     <filter-name>RCFilter</filter-name>
     <filter-class>RCFilter</filter-class>
   </filter>
   <filter-mapping>
     <filter-name>RCFilter</filter-name>
     <url-pattern>/admin/*</url-pattern>
   </filter-mapping>
 </web-app>

web.xml