javaWeb----Filter------分ip统计访问次数

注意事项：
1、在show.jsp中使用的是applicationScope而不是application
2、注意web.xml中的配置信息，不要配错
3、在AFilter中获取session的方式

AFilter

package cn.itcast.web.filter;

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;

/**
 * 从application中获取Map
 * 从request中得到当前客户端的IP
 * 进行统计工作，结果保存到Map中
 * @author cxf
 *
 */
public class AFilter implements Filter {
    private FilterConfig config;
    public void destroy() {
    }

    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        /*
         * 1. 得到application中的map
         * 2. 从request中获取当前客户端的ip地址
         * 3. 查看map中是否存在这个ip对应访问次数，如果存在，把次数+1再保存回去
         * 4. 如果不存在这个ip，那么说明是第一次访问本站，设置访问次数为1
         */
        /*
         * 1. 得到appliction
         */
        ServletContext app = config.getServletContext();
        Map<String,Integer> map = (Map<String, Integer>) app.getAttribute("map");
        /*
         * 2. 获取客户端的ip地址
         */
        String ip = request.getRemoteAddr();
        /*
         * 3. 进行判断
         */
        if(map.containsKey(ip)) {//这个ip在map中存在，说明不是第一次访问
            int cnt = map.get(ip);
            map.put(ip, cnt+1);
        } else {//这个ip在map中不存在，说明是第一次访问
            map.put(ip, 1);
        }
        app.setAttribute("map", map);//把map再放回到app中

        chain.doFilter(request, response);//肯定放行
    }

    /**
     * 在服务器启动时就会执行本方法，而且本方法只执行一次！
     */
    public void init(FilterConfig fConfig) throws ServletException {
        this.config = fConfig;
    }
}

AListener

package cn.itcast.web.listener;

import java.util.LinkedHashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class AListener implements ServletContextListener {
    /**
     * 在服务器启动时创建Map，保存到ServletContext
     */
    public void contextInitialized(ServletContextEvent sce) {
        // 创建Map
        Map<String,Integer> map = new LinkedHashMap<String,Integer>();
        // 得到ServletContext
        ServletContext application = sce.getServletContext();
        // 把map保存到application中
        application.setAttribute("map", map);
    }

    public void contextDestroyed(ServletContextEvent sce) {
    }
}

web.xml

<?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>
  <filter>
    <display-name>AFilter</display-name>
    <filter-name>AFilter</filter-name>
    <filter-class>cn.itcast.web.filter.AFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>AFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <listener>
    <listener-class>cn.itcast.web.listener.AListener</listener-class>
  </listener>
</web-app>

show.jsp

<%@ 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">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->

  </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>

javaWeb----Filter------分ip统计访问次数

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