自定义过滤器

首先在web.xml中对过滤器的监听

 1 <!-- 自定义过滤器 -->
 2   <filter>
 3       <filter-name>AscFilter</filter-name>
 4       <filter-class>com.llh.filter.AscFilter</filter-class>
 5   </filter>
 6   <filter-mapping>
 7       <filter-name>AscFilter</filter-name>
 8       <url-pattern>/main.jsp</url-pattern>
 9   </filter-mapping>
10

新建一个包com.llh.filter,创建一个实现Filter接口的类

 1 package com.llh.filter;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.Filter;
 6 import javax.servlet.FilterChain;
 7 import javax.servlet.FilterConfig;
 8 import javax.servlet.ServletException;
 9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13 
14 import com.llh.entity.Student;
15 
16 /**
17  * 过滤登陆
18  * 
19  * @author Administrator
20  *
21  */
22 public class AscFilter implements Filter {
23     @Override
24     public void init(FilterConfig filterConfig) throws ServletException {
25         // TODO Auto-generated method stub
26     }
27 
28     @Override
29     public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
30             throws IOException, ServletException {
31         // TODO Auto-generated method stub
32         HttpServletRequest request = (HttpServletRequest) req;
33         HttpServletResponse response = (HttpServletResponse) resp;
34         Student s = (Student) request.getSession().getAttribute("s");
35         System.out.println("lanj");
36         if(s==null){
37             System.out.println("拦截了");
38             response.sendRedirect("login.jsp");
39         }
40         chain.doFilter(request, response);
41     }
42     
43     @Override
44     public void destroy() {
45         // TODO Auto-generated method stub
46     }
47 
48 }