filter应用案例一：分IP统计访问次数

时间：2021-08-09 20:15:13

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：

 import java.util.HashMap;

 import java.util.Map;

 import javax.servlet.ServletContext;

 import javax.servlet.ServletContextEvent;

 import javax.servlet.ServletContextListener;

 public class MyListener implements ServletContextListener {

     public void contextInitialized(ServletContextEvent sce) {

         ServletContext application= sce.getServletContext();

         Map<String, Integer>map=new HashMap<String, Integer>();

         application.setAttribute("map", map);

     }

     public void contextDestroyed(ServletContextEvent sce) {

     }

 }

MyListener

 import java.io.IOException;

 import java.util.Map;

 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;

 public class CountIPFilter implements Filter {

     private FilterConfig config;

     public void destroy() {}

     public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

         ServletContext application= config.getServletContext();

         Map<String, Integer>map=(Map<String, Integer>) application.getAttribute("map");

         String ip=request.getRemoteAddr();

         if(map.containsKey(ip))

         {

             int t=map.get(ip);

             map.put(ip, t+1);

         }

         else map.put(ip, 1);

         chain.doFilter(request, response);

     }

     public void init(FilterConfig fConfig) throws ServletException {

         config=fConfig;

     }

 }

CountIPFilter

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

 <html>

   <head>

     <title>My JSP 'show.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">

   </head>

   <body>

 <h1 align="center">显示结果</h1>

 <table align="center" width="60%" border="1">

     <tr>

         <th>IP</th>

         <th>次数</th>

     </tr>

 <c:forEach items="${applicationScope.map }" var="entry">

     <tr>

         <td>${entry.key }</td>

         <td>${entry.value }</td>

     </tr>

 </c:forEach>

 </table>

   </body>

 </html>

show.jsp

 <?xml version="1.0" encoding="UTF-8"?>

 <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">

   <display-name></display-name>

   <welcome-file-list>

     <welcome-file>index.jsp</welcome-file>

   </welcome-file-list>

   <listener>

     <listener-class>MyListener</listener-class>

   </listener>

   <filter>

     <display-name>CountIPFilter</display-name>

     <filter-name>CountIPFilter</filter-name>

     <filter-class>CountIPFilter</filter-class>

   </filter>

   <filter-mapping>

     <filter-name>CountIPFilter</filter-name>

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

   </filter-mapping>

 </web-app>

web.xml

运行示例：

filter应用案例一：分IP统计访问次数

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