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创建一个过滤器实现javax.servlet.Filter接口。
package com.lyq; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; public class CountFilter implements Filter{ //来访数量 private int count; public void destroy() { } public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { count++; //访问数量自增 //将ServletRequest转换成HttpServletRequest HttpServletRequest req = (HttpServletRequest)request; //获取ServletContext ServletContext context = req.getSession().getServletContext(); context.setAttribute("count", count); //将访问数量放入到ServletContext中 chain.doFilter(request, response); //向下传递过滤器 } public void init(FilterConfig filterConfig) throws ServletException { String param = filterConfig.getInitParameter("count"); //获取初始化参数 count = Integer.valueOf(param); //将字符串转换为int } }
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <display-name></display-name> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <!-- 过滤器声明 --> <filter> <filter-name>CountFilter</filter-name> <filter-class>com.lyq.CountFilter</filter-class> <init-param> <param-name>count</param-name> <param-value>5000</param-value> </init-param> </filter> <filter-mapping> <filter-name>CountFilter</filter-name> <url-pattern>/index.jsp</url-pattern> </filter-mapping> </web-app>
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP ‘index.jsp‘ starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> </head> <body> <h2> 欢迎光临,<br> 你是本站的第【 <%=application.getAttribute("count") %> 】位访客!</h2> </body> </html>
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原文地址：http://www.cnblogs.com/rixiang/p/4734256.html
