详细说下过滤器：

对于后台系统，为了防止用户直接在地址栏发请求获取后台数据页面。需要强制要求其登录这样就用到了过滤器，今天结合一个实例来说明

下面是代码：

package com.jt.xiaoyang.util;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

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;
import javax.servlet.http.HttpSession;

/**   
* 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面    
* filter中配置参数    
* checkSessionKey 需检查的在 Session 中保存的关键字   
  
* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath   
  
* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath   
*/   
public class CheckLoginFilter  implements Filter{
	
      protected FilterConfig filterConfig = null;    
      private String redirectURL = null;    
      private List notCheckURLList = new ArrayList();    
      private String sessionKey = null;    
   
      public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException{    
		    HttpServletRequest request   = (HttpServletRequest) servletRequest;    
		    HttpServletResponse response = (HttpServletResponse) servletResponse;    
		    HttpSession session = request.getSession();    
		    if(sessionKey == null){    
			     filterChain.doFilter(request, response);    
			     return;    
		    } 
		    //登录检查【检查请求是否在列表中】
		    if((checkRequestURIIntNotFilterList(request))){   //如果在检查列表中
		    	if(session.getAttribute(sessionKey) == null){ //并且没有登录
		    		response.sendRedirect(request.getContextPath() + redirectURL);    
		    		return;    
		    	}
		    }    
		    filterChain.doFilter(servletRequest, servletResponse);    
		}    
   
		public void destroy(){    
		    notCheckURLList.clear();    
		}    
   
		private boolean checkRequestURIIntNotFilterList(HttpServletRequest request){  
			//            /user/list/0.do    /login.do
		    String uri = request.getServletPath() + (request.getPathInfo() == null ? "" : request.getPathInfo());
		    int last = uri.lastIndexOf("/");
		    uri = uri.substring(0, last);//user/list
		    	return notCheckURLList.contains(uri);    
		   
		}    

		public void init(FilterConfig filterConfig) throws ServletException{    
		    this.filterConfig = filterConfig;    
		    redirectURL = filterConfig.getInitParameter("redirectURL");    
		    sessionKey =  filterConfig.getInitParameter("checkSessionKey");    
		    String notCheckURLListStr = filterConfig.getInitParameter("notCheckURLList");    
		    if(notCheckURLListStr != null){
			     StringTokenizer st = new StringTokenizer(notCheckURLListStr, ";");    
			     notCheckURLList.clear();    
			     while(st.hasMoreTokens()){    
			    	 notCheckURLList.add(st.nextToken());    
			     }    
		    }    
		}    
}    

这样的话就实现了，对请求的过虑

其实这个功能用拦截器也可以做，比如我们用了spring的框架，则就可以这样配置

综上所述，其实拦截器和过滤去很多时候可以实现相同的功能

没有严格的区别