关于Filter需要注意的问题

过滤器是特殊的servlet，和一般的servlet在参数方面有一些区别如下：

 

对于一般的servlet：参数是HttpServletRequest和HttpServletResponse，而且继承了javax.servlet.http.HttpServlet

对于Filter            ：参数是  ServletRequest和ServletRespnse,实现了javax.servlet.Filter接口

 

 

如下：

一般的servlet：

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Ser extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException

}

 

 

Filter：

 

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class F implements Filter {

 public void doFilter(ServletRequest arg0, ServletResponse arg1,
   FilterChain arg2) throws IOException, ServletException {
HttpServletRequest request=(HttpServletRequest)arg0;//如果需要，可以这样得到HttpServletRequest实例

 }