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

}