<filter>

  <filter-name>UsersFilter</filter-name>

  <filter-class>com.web.UsersFilter</filter-class>

 </filter>

 <filter-mapping>

  <filter-name>UsersFilter</filter-name>

  <url-pattern>/*</url-pattern>

 </filter-mapping> 

package com.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;

import javax.servlet.http.HttpSession;

public class UsersFilter implements Filter {

    public void doFilter(ServletRequest request, ServletResponse response,

            FilterChain chain) throws IOException, ServletException {

        // 设置请求的字符编码

        request.setCharacterEncoding("UTF-8");

        // 设置返回请求的字符编码

        response.setCharacterEncoding("UTF-8");

        // 转换ServletRequest为 HttpServletRequest

        HttpServletRequest req = (HttpServletRequest) request;

        // 转换ServletResponse为HttpServletRequest

        HttpServletResponse res = (HttpServletResponse) response;

        // 获取Session

        HttpSession session = req.getSession();

        // 获取Session中存储的对象

        Object o = session.getAttribute("user");

        // 获取当前请求的URI

        String url = req.getRequestURI();

        // 判断Session中的对象是否为空；判断请求的URI是否为不允许过滤的URI

        if (o==null && url.indexOf("test.jsp")<0

                && url.indexOf("comment.jsp")<0

                && url.indexOf("link.jsp")<0) {

            chain.doFilter(request, response);

            res.setHeader("Cache-Control","no-store");

            res.setDateHeader("Expires",0);

            res.setHeader("Pragma","no-cache");

            res.flushBuffer();

            }

    }

    public void destroy() {

        // TODO Auto-generated method stub

    }

    public void init(FilterConfig arg0) throws ServletException {

        // TODO Auto-generated method stub

    }   

}