ServletContext设置全局变量实现统计站点访问次数

package com.fl.servlet;


import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HttpServletDemo02 extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        ServletContext sc = getServletContext();
        Integer click_num =(Integer) sc.getAttribute("clicknum");
        if(click_num == null)
            sc.setAttribute("clicknum", 1); //在全局区域设置一个名为clicknum的属性，值为1。
        else
            sc.setAttribute("clicknum", ++click_num);
            System.out.println(click_num);
    }
    @Override
    public void init(ServletConfig config) throws ServletException {
        ServletContext sc = config.getServletContext();
        String temp = sc.getInitParameter("kkkk");
        System.out.println(temp);
    }
}

<?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">
  <servlet>
    <servlet-name>HttpServletDemo02</servlet-name>
    <servlet-class>com.fl.servlet.HttpServletDemo02</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  
  <servlet-mapping>
    <servlet-name>HttpServletDemo02</servlet-name>
    <url-pattern>/servlet/HttpServletDemo02</url-pattern>
  </servlet-mapping>
</web-app>