filter应用案例一：分IP统计访问次数

统计工作需要在所有资源之前都执行，那么就可以放到Filter中了。
用Map<String,Integer>装载统计的数据。Map创建时间（使用ServletContextListener，在服务器启动时完成创建），Map保存到ServletContext中！！Map需要在Filter中用来保存数据

代码：

 1 import java.util.HashMap;
 2 import java.util.Map;
 3 
 4 import javax.servlet.ServletContext;
 5 import javax.servlet.ServletContextEvent;
 6 import javax.servlet.ServletContextListener;
 7 
 8 public class MyListener implements ServletContextListener {
 9     public void contextInitialized(ServletContextEvent sce) {
10         ServletContext application= sce.getServletContext();
11         Map<String, Integer>map=new HashMap<String, Integer>();
12         application.setAttribute("map", map);
13     }
14 
15     public void contextDestroyed(ServletContextEvent sce) {
16     }
17     
18 }
MyListener 
 1 import java.io.IOException;
 2 import java.util.Map;
 3 
 4 import javax.servlet.Filter;
 5 import javax.servlet.FilterChain;
 6 import javax.servlet.FilterConfig;
 7 import javax.servlet.ServletContext;
 8 import javax.servlet.ServletException;
 9 import javax.servlet.ServletRequest;
10 import javax.servlet.ServletResponse;
11 
12 public class CountIPFilter implements Filter {
13 
14     private FilterConfig config;
15     public void destroy() {}
16 
17     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
18         ServletContext application= config.getServletContext();
19         Map<String, Integer>map=(Map<String, Integer>) application.getAttribute("map");
20         String ip=request.getRemoteAddr();
21         if(map.containsKey(ip))
22         {
23             int t=map.get(ip);
24             map.put(ip, t+1);
25         }
26         else map.put(ip, 1);
27         chain.doFilter(request, response);
28     }
29 
30     public void init(FilterConfig fConfig) throws ServletException {
31         config=fConfig;
32     }
33 
34 }
CountIPFilter
 1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
 2 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
 3 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 4 <html>
 5   <head>
 6     <title>My JSP 'show.jsp' starting page</title>
 7     <meta http-equiv="pragma" content="no-cache">
 8     <meta http-equiv="cache-control" content="no-cache">
 9     <meta http-equiv="expires" content="0">    
10     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
11     <meta http-equiv="description" content="This is my page">
12   </head>
13   <body>
14 <h1 align="center">显示结果</h1>
15 <table align="center" width="60%" border="1">
16     <tr>
17         <th>IP</th>
18         <th>次数</th>
19     </tr>
20 <c:forEach items="${applicationScope.map }" var="entry">
21     <tr>
22         <td>${entry.key }</td>
23         <td>${entry.value }</td>
24     </tr>
25 </c:forEach>
26 </table>
27   </body>
28 </html>
show.jsp
 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
 3   <display-name></display-name>
 4   <welcome-file-list>
 5     <welcome-file>index.jsp</welcome-file>
 6   </welcome-file-list>
 7   <listener>
 8     <listener-class>MyListener</listener-class>
 9   </listener>
10   <filter>
11     <display-name>CountIPFilter</display-name>
12     <filter-name>CountIPFilter</filter-name>
13     <filter-class>CountIPFilter</filter-class>
14   </filter>
15   <filter-mapping>
16     <filter-name>CountIPFilter</filter-name>
17     <url-pattern>/*</url-pattern>
18   </filter-mapping>
19 </web-app>
web.xml

运行示例：

posted @ 2016-11-17 19:29  凌晨。。。三点  阅读(343)  评论(0)  编辑  收藏  举报