过滤器的使用

 首先写好类:它继承

ackage shop;

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 class MyFilter implements Filter ...{
    protected FilterConfig filterConfig;

    public void init(FilterConfig arg0) throws ServletException ...{
        filterConfig = arg0;


    }

    public void doFilter(ServletRequest arg0, ServletResponse arg1,
            FilterChain arg2) throws IOException, ServletException ...{
        HttpServletRequest request = (HttpServletRequest) arg0;
          HttpServletResponse response = (HttpServletResponse) arg1;
          String tag=(String)request.getSession().getAttribute("isLog");
        
        if((tag!=null)&&(tag.equals("ok")))
        ...{
            
                arg2.doFilter(arg0, arg1);
        }
        
        else
        ...{
              System.out.println("被拦截一个未认证的请求");
              response.sendRedirect("/web/form/login.jsp");
         }

    }

    public void destroy() ...{
        filterConfig = null;
    }
    public void setFilterConfig(FilterConfig filterConfig) ...{
        this.filterConfig = filterConfig;
    }

}

接下来就是在web.xml中配置就可以了:

 

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.4" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee   http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  

<filter>
  <filter-name>MyFilter</filter-name> 
  <filter-class>shop.MyFilter</filter-class> 
  </filter>
 <filter-mapping>
  <filter-name>MyFilter</filter-name> 
  <url-pattern>/form/shopping.jsp</url-pattern> 
  </filter-mapping>
   <filter-mapping>
  <filter-name>MyFilter</filter-name> 
  <url-pattern>/form/checkout.jsp</url-pattern> 
  </filter-mapping>