/*
 * MyFilter.java
 * 过滤器
 */
package com.baidu.web;

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{

 @Override
 public void destroy() {
 }

 @Override
 public void doFilter(ServletRequest request, ServletResponse response,
 FilterChain chain) throws IOException, ServletException {
 //对请求request进行处理
 HttpServletResponse resp = (HttpServletResponse)response;
 HttpServletRequest req = (HttpServletRequest) request;
 String username = (String) req.getSession().getAttribute("username");
 if(req.getRequestURI().contains("Buy") || req.getRequestURI().contains("collect")){
 if(username==null || username.equals("")){ //满足过滤要求，进行处理
 req.getRequestDispatcher("/login.jsp").forward(req, resp);
 return;
 }
 }
 chain.doFilter(req, resp);
 //对相应response进行处理
 }

 @Override
 public void init(FilterConfig filterConfig) throws ServletException {
 //filterConfig，通过filterConfig的getServletContext() 方法可以获得 ServletContext
 }
}
 

<filter>
 <filter-name>filter</filter-name>
 <filter-class>com.baidu.web.MyFilter</filter-class>
 </filter>
 <filter-mapping>
 <filter-name>filter</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>