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統(tǒng)計(jì)用戶(hù)在線人數(shù)

在統(tǒng)計(jì)用戶(hù)在人數(shù)的時(shí)候，我們用到了監(jiān)聽(tīng)器，監(jiān)聽(tīng)器大致分為以下三種：

1.  

    

   ServletRequestListener：用于監(jiān)聽(tīng)請(qǐng)求的監(jiān)聽(tīng)接口

    

2.  

    

   HttpSessionListener：用于監(jiān)聽(tīng)會(huì)話的監(jiān)聽(tīng)接口

    

3.  

    

   ServletContextListener：用于監(jiān)聽(tīng)?wèi)?yīng)用的回話接口

    

監(jiān)聽(tīng)Request域

這種統(tǒng)計(jì)辦法是錯(cuò)誤的認(rèn)為每次刷新頁(yè)面后進(jìn)行進(jìn)行一次的count++運(yùn)算

import JAVAx.servlet.*;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener()
public class MyRequestListener implements ServletRequestListener{
private ServletContext sc;
private Integer count;
@Override
//請(qǐng)求被初始化 Request
public void requestInitialized(ServletRequestEvent sre) {
//獲取全局域
sc = sre.getServletContext();
//將count從全局域中獲取出來(lái)
count = (Integer) sc.getAttribute("count");
System.out.println(count);
count++;
System.out.println(count);
sc.setAttribute("count",count);
}
}
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener()
public class MyServletContextListener implements ServletContextListener{
private ServletContext sc;
@Override
//Application被初始化的時(shí)候創(chuàng)建
public void contextInitialized(ServletContextEvent sce) {
Integer count = 0;
//獲取全局域
sc = sce.getServletContext();
//將count放入到全局域中
sc.setAttribute("count",count);
}
}
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$title>
head>

You are the ${applicationScope.count} customer to visit. h1>center>
body>
html>

這種錯(cuò)誤地做法導(dǎo)致的是每刷新一次頁(yè)面 就會(huì)導(dǎo)致count進(jìn)行累加操作，最終產(chǎn)生錯(cuò)誤的在線人數(shù)，所以此時(shí)想到不應(yīng)該監(jiān)聽(tīng)Request域，而應(yīng)該監(jiān)聽(tīng)Session域。

監(jiān)聽(tīng)Session域

在第二次監(jiān)聽(tīng)Session域之后，發(fā)現(xiàn)每次刷新頁(yè)面后不改變count但是在啟動(dòng)不同的瀏覽器后count++會(huì)實(shí)現(xiàn)，但是，這樣做并不是我們要統(tǒng)計(jì)的在線人數(shù)，所以此種做法錯(cuò)誤。由于代碼只是將原來(lái)寫(xiě)在Request監(jiān)聽(tīng)器中的代碼轉(zhuǎn)移到Session監(jiān)聽(tīng)器中，所以其他沒(méi)變的代碼將不重復(fù)。

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener()
public class MySessionListener implements HttpSessionListener{

private ServletContext sc;
private Integer count;

@Override
//當(dāng)對(duì)話產(chǎn)生時(shí)激活此方法
public void sessionCreated(HttpSessionEvent se) {
sc = se.getSession().getServletContext();
count = (Integer) sc.getAttribute("count");
count++;
sc.setAttribute("count",count);
}
}

這時(shí)我們發(fā)現(xiàn)對(duì)于在線人數(shù)的統(tǒng)計(jì)，不是網(wǎng)頁(yè)訪問(wèn)的次數(shù)，也不是瀏覽器打開(kāi)的個(gè)數(shù)，對(duì)需求的理解的錯(cuò)誤理解。所以正確的做法是統(tǒng)計(jì)其IP的數(shù)量，這樣的話，不管你在一臺(tái)電腦上開(kāi)啟多少客戶(hù)端，都會(huì)只有一個(gè)。

正確的統(tǒng)計(jì)方法

統(tǒng)計(jì)其IP的數(shù)量，將IP的數(shù)量作為當(dāng)前的在線人數(shù)，那么如何統(tǒng)計(jì)IP的數(shù)量呢？這樣將會(huì)導(dǎo)出以下問(wèn)題：

•  

  如何獲取用戶(hù)的IP？

   

•  

  IP將如何存儲(chǔ)？

   

•  

  如何判斷IP之前已經(jīng)存在？

   

現(xiàn)在來(lái)解決這些問(wèn)題：

•  

  只能從請(qǐng)求中獲取

   

•  

  通過(guò)2、3問(wèn)題，我們想到了集合（List），因?yàn)榧喜粌H可以存儲(chǔ)任何字符串，還可以通過(guò)遍歷來(lái)判斷之前是否有重復(fù)的IP出現(xiàn)。

   

到了這里又冒出來(lái)一個(gè)問(wèn)題集合（List）放到哪個(gè)域里呢？

ServletContext域

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;
import java.util.ArrayList;
import java.util.List;

@WebListener()
public class MyServletContextListener implements ServletContextListener{
private ServletContext sc;

@Override
//Application被初始化的時(shí)候創(chuàng)建
public void contextInitialized(ServletContextEvent sce) {
//創(chuàng)建一個(gè)鏈表來(lái)存儲(chǔ)IP
List ips = new ArrayList<>();
sc = sce.getServletContext();
//將創(chuàng)建好的鏈表對(duì)象，放到Application域中
sc.setAttribute("ips",ips);
}
}

由于IP只能在Request域中獲取，所以遍歷判斷在Request域中進(jìn)行。公眾 號(hào)Java精選，回復(fù)java面試，獲取面試資料，支持在線刷題。

import javax.servlet.*;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.*;
import java.util.List;

@WebListener()
public class MyRequestListener implements ServletRequestListener{

private HttpServletRequest sr;
private String clientIp;
private ServletContext sc;
private List ips;
private HttpSession session;

@Override
//請(qǐng)求被初始化 Request
public void requestInitialized(ServletRequestEvent sre) {
//從請(qǐng)求域中獲取IP
sr = (HttpServletRequest) sre.getServletRequest();
clientIp = sr.getRemoteAddr();
session = sr.getSession();
session.setAttribute("clientIp",clientIp);

//測(cè)試
// System.out.println("clientIp = "+ clientIp);
//獲取Application域中的List
sc = sre.getServletContext();
ips = (List) sc.getAttribute("ips");
//遍歷ips
for (String ip :
ips) {
if (clientIp.equals(ip))
return;
}
ips.add(clientIp);
sc.setAttribute("ips",ips);
}
}

因?yàn)橐y(tǒng)計(jì)在線人數(shù)，所以要設(shè)置退出按鈕，點(diǎn)擊退出按鈕之后，因?yàn)橐獜腖ist域中移除，所以使用Session域監(jiān)聽(tīng)器來(lái)判斷session回話的關(guān)閉

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.*;
import java.util.List;

@WebListener()
public class MySessionListener implements HttpSessionListener{

private ServletContext sc;
private List ips;
private HttpSession session;
private Object clientIp;

@Override
public void sessionDestroyed(HttpSessionEvent se) {
sc = se.getSession().getServletContext();
ips = (List) sc.getAttribute("ips");
session = se.getSession();
clientIp = session.getAttribute("clientIp");
//刪除ip，如何獲取IP，但是不可以從session獲取到IP
//因?yàn)镾ession獲取不到Request
//一個(gè)Session包含多個(gè)Request
//一個(gè)Request只對(duì)應(yīng)一個(gè)Session 所以獲取不到，這時(shí)只能先從Request域中獲取到的ips，放置到Session域
//然后從Session 域中讀取
ips.remove(clientIp);
// session一失效就馬上將此IP從鏈表中移除是錯(cuò)誤的
//應(yīng)該看此IP是否有另外的回話存在，如果有的話不能刪除
}
}

此處代碼是頁(yè)面點(diǎn)擊關(guān)閉后，激活的退出方法

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(name = "LogoutServlet",urlPatterns = "/logoutServlet")
public class LogoutServlet extends HttpServlet {

private HttpSession session;

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//從域中獲取一個(gè)session，設(shè)置為false 如果域中存在一個(gè)session，則直接獲取，如果不存在，則返回一個(gè)空的session
session = request.getSession(false);
if (session != null){
//使session失效
session.invalidate();
//失效后，需要進(jìn)行的操作，List鏈表中需要減去，用到了Session域監(jiān)聽(tīng)器
}
}

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
}

在jsp頁(yè)面進(jìn)行讀取的時(shí)候，因?yàn)閕ps是以List鏈表的形式存在的，所以要想判斷當(dāng)前在線人數(shù)，所以必須要判斷鏈表的長(zhǎng)度，所以是applicationScope.ips.size()

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$title>
head>
You are the ${applicationScope.ips.size()} customer to visit. h1>
安全退出
a>h3>
center>
body>
html>

好了?，這時(shí)候，程序?qū)懲炅耍绾闻袛嗄兀?/code>