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用Java程序
現(xiàn)在許多網(wǎng)站都必須統(tǒng)計(jì)瀏覽量，在此為了記錄當(dāng)前在線人數(shù)，我設(shè)計(jì)了一個(gè)計(jì)數(shù)器。其功能是：計(jì)數(shù)器就將自動(dòng)加一，離開時(shí)就自動(dòng)減一。。
這里就做了個(gè)很小的demo:
Java 代碼如下：

package com.dr.demo2.servlet;

import java.io.IOException;
import java.sql.Timestamp;
import java.util.ArrayList;

import javax.servlet.ServletException;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

import org.apache.log4j.Logger;

public class SessionCounter implements HttpSessionListener,
ServletRequestListener {
private static Logger log = Logger.getLogger(SessionCounter.class);
private static final String CONTENT_TYPE = "text/html; charset=GBK";
private static int activeSessions = 0;// 當(dāng)前活動(dòng)的人數(shù)
private HttpServletRequest request;
private static ArrayList list = new ArrayList();// 用來存放不同ip的地址

public void init() throws ServletException {
log.info("SessionCounter init!");

}

public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  log.info("SessionCounter doGet!");
  response.setContentType(CONTENT_TYPE);
  HttpSession session = request.getSession();
}

public void destroy() {
log.info("SessionCounter destroy!");
}

public void requestDestroyed(ServletRequestEvent event) {
  // To change body of implemented methods use File | Settings | File
  // Templates.
  log.info("SessionCounter requestDestroyed!");
}

public void requestInitialized(ServletRequestEvent sre) {
request = (HttpServletRequest) sre.getServletRequest();
log.info("SessionCounter requestInitialized!");
}

public void sessionCreated(HttpSessionEvent httpSessionEvent) {
  log.info("SessionCounter sessionCreater!");
  String sessionId = httpSessionEvent.getSession().getId();
  Timestamp createTime = new Timestamp(System.currentTimeMillis());
  String loginIp = request.getRemoteAddr();
  boolean rs = true;
  if (list.size() > 0) {
   for (int i = 0; i < list.size(); i++) {
    if (loginIp.equals(list.get(i))) {
     rs = false;
    }
   }
  }
  if (rs) { // 如果隊(duì)列中存在相同的IP 則SESSION不增加
   list.add(loginIp);
   log.info("ipList隊(duì)列新增ip: " + loginIp);
   activeSessions++;
   log.info("新增SESSION,sessionId = " + sessionId + "; createTime = "
     + createTime + "; loginIp = " + loginIp + "; 當(dāng)前總SESSION值為 "
     + activeSessions);
  }
}

public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
  log.info("SessionCounter sessionDestroyed!");
  String sessionId = httpSessionEvent.getSession().getId();
  Timestamp overTime = new Timestamp(System.currentTimeMillis());
  String loginIp = request.getRemoteAddr();
  if (activeSessions > 0) {
   if (list.size() > 0) {
    for (int i = 0; i < list.size(); i++) {
     if (loginIp.equals(list.get(i))) {
      list.remove(i);
      log.info("ipList隊(duì)列移除ip: " + loginIp);
     }
    }
   }
   activeSessions--; // 在用戶銷毀的時(shí)候,從隊(duì)列中踢出這個(gè)IP
   log.info("銷毀SESSION,sessionId = " + sessionId + "; overTime = "
     + overTime + "; loginIp = " + loginIp + "; 當(dāng)前總SESSION值為 "
     + activeSessions);
  }
}

public static int getActiveSessions() {
log.info("SessionCounter getActiveSessions!");
return activeSessions;
}

public void setActiveSessions(int i) {
log.info("SessionCounter setActiveSessions!");
activeSessions = i;
}

}

jsp 部分代碼

<%@ 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 'online.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>
<%@ page import= "com.dr.demo2.servlet.SessionCounter" %>
在線： <%= SessionCounter.getActiveSessions() %>人
</body>
</html>

啟動(dòng)tomcat ,在瀏覽器中輸入：http://127.0.0.1:8080/OnlineCount/online.jsp

執(zhí)行效果如下：