学步园

package servletText;

import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class FirstFilter implements Filter
{
public void init(FilterConfig filterConfig)
           throws ServletException
{
   System.out.println("** 过滤器初始化...") ;
}
public void doFilter(ServletRequest request,
                      ServletResponse response,
                      FilterChain chain)
               throws IOException,
                      ServletException
{
   HttpServletRequest req=(HttpServletRequest)request;
   HttpSession session=req.getSession();
   if(session.getAttribute("name")!=null)
   {
   System.out.println("** 过滤器 doFilter (chain之前)...") ;
   chain.doFilter(request,response) ;
   System.out.println("** 过滤器 doFilter (chain之后)...") ;
   }
   else
   {
    System.out.println("失败得登陆") ;
    chain.doFilter(request,response) ;
   }
}
public void destroy()
{
   System.out.println("** 过滤器销毁...") ;
}
}

在xml中得代码

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
   <filter>
<filter-name>text</filter-name>
<filter-class>servletText.FirstFilter</filter-class>
   </filter>
     <filter-mapping>
<filter-name>text</filter-name>
<url-pattern>/*</url-pattern>
   </filter-mapping>
</web-app>