?這是javaweb教學(xué)書(shū)上的一道題，要求統(tǒng)計(jì)在線人數(shù)，同時(shí)顯示當(dāng)前在線的每個(gè)用戶的信息，類似于達(dá)到這樣的效果：
javaweb.png
?關(guān)于在線人數(shù)的統(tǒng)計(jì)可以創(chuàng)建一個(gè)會(huì)話監(jiān)聽(tīng)器OnlineListener它實(shí)現(xiàn)了HttpSessionListener接口，每當(dāng)有會(huì)話創(chuàng)建時(shí)則，就會(huì)調(diào)用sessionCreated()方法，然后在里面對(duì)OnlineCount加1，當(dāng)會(huì)話被銷毀時(shí)調(diào)用sessionDestroyed()，對(duì)OnlineCount減1，再將OnlineCount保存為ServletContext屬性
?同時(shí)需要顯示每一個(gè)用戶的信息，所以需要對(duì)每一個(gè)用戶的會(huì)話進(jìn)行記錄，我認(rèn)為可以用SessionID去代表每一個(gè)用戶，然后將每一個(gè)會(huì)話的SessionID和Session對(duì)應(yīng)起來(lái)，這里可以用一個(gè)map集合，將id作為鍵。所以我這里創(chuàng)建了一個(gè)MySession類專門(mén)用于對(duì)Session進(jìn)行管理，即保存Session同時(shí)根據(jù)SessionID得到Session。最后在顯示頁(yè)面Servlet里進(jìn)行遍歷，獲取用戶信息。
以下是相關(guān)代碼實(shí)現(xiàn)：
這是用戶需要提交的表單的簡(jiǎn)單實(shí)現(xiàn)：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=GBK">
<title>Insert title here</title>
</head>
<body>
<form action="/TomcatTest/guest.do" method="post">
name:<input type="text" name="name"><br>
message:<input type="text" name="message"><br>
<input type="submit" name="submit" value="send">
</form>
</body>
</html>
這是監(jiān)聽(tīng)器的實(shí)現(xiàn)：
package com.zoro.listener;
import java.util.Date;
import java.util.LinkedList;
import java.util.List;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
//監(jiān)聽(tīng)器的實(shí)現(xiàn)
//實(shí)現(xiàn)在線人數(shù)的統(tǒng)計(jì)
public class OnlineListener implements HttpSessionListener {
public static int onlineCount;
public OnlineListener(){
onlineCount = 0;
}
/*會(huì)話session創(chuàng)建時(shí)處理*/
public void sessionCreated(HttpSessionEvent sessionEvent){
//每創(chuàng)建一個(gè)會(huì)話count加1
onlineCount++;
//獲取當(dāng)前會(huì)話，進(jìn)行會(huì)話管理
HttpSession session = sessionEvent.getSession();
//添加session
MySessionContext.AddSession(session);
//由session獲取會(huì)話，并將在線人數(shù)設(shè)置為ServletContext屬性
session.getServletContext().setAttribute("online", new Integer(onlineCount));
System.out.println("online people:"+onlineCount);
//獲取會(huì)話創(chuàng)建時(shí)間
long a = session.getCreationTime();
Date createTime = new Date(a);
System.out.println(createTime);
//將會(huì)話創(chuàng)建時(shí)間設(shè)置為會(huì)話屬性
session.setAttribute("createTime", createTime);
}
/*會(huì)話銷毀時(shí)處理*/
public void sessionDestroyed(HttpSessionEvent sessionEvent){
onlineCount--;
HttpSession session = sessionEvent.getSession();
System.out.println("one session is destroyed");
sessionEvent.getSession().getServletContext().setAttribute("online", new Integer(onlineCount));
//從會(huì)話列表中刪除銷毀的會(huì)話
MySessionContext.DelSession(session);
}
}
這是MySessionContext的實(shí)現(xiàn)，用于對(duì)Session進(jìn)行管理：
package com.zoro.listener;
import java.util.HashMap;
import javax.servlet.http.HttpSession;
/*用于對(duì)會(huì)話session進(jìn)行存儲(chǔ)管理*/
public class MySessionContext {
//創(chuàng)建一個(gè)靜態(tài)的hashmap用于存儲(chǔ)
private static HashMap mymap = new HashMap();
/*將sessionID和session添加至map中*/
public static synchronized void AddSession(HttpSession session) {
if (session != null) {
mymap.put(session.getId(), session);
}
}
/*根據(jù)sessionID從map中刪除session*/
public static synchronized void DelSession(HttpSession session) {
if (session != null) {
mymap.remove(session.getId());
}
}
/*根據(jù)sessionID獲取session*/
public static synchronized HttpSession getSession(String session_id) {
if (session_id == null)
return null;
return (HttpSession) mymap.get(session_id);
}
/*獲取存儲(chǔ)session的map*/
public static synchronized HashMap getIdMap(){
return mymap;
}
}
這是用于顯示的Servlet：
package com.zoro.wrap;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.zoro.listener.*;
public class guestServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//通過(guò)request對(duì)象獲取會(huì)話信息
HttpSession session = req.getSession();
//設(shè)置瀏覽器在多久沒(méi)有請(qǐng)求的情況下，httpsession自動(dòng)失效
//session.setMaxInactiveInterval(30);
//創(chuàng)建日期對(duì)象存儲(chǔ)會(huì)話創(chuàng)建時(shí)的日期
Date date = (Date)(session.getAttribute("createTime"));
//獲取用戶瀏覽器的相關(guān)信息
String userAgent = req.getHeader("user-agent");
//將想關(guān)信息設(shè)置為會(huì)話屬性
session.setAttribute("info",userAgent );
//獲取會(huì)話ID
String id = session.getId();
System.out.println("id:"+id);
//將會(huì)話id存儲(chǔ)為會(huì)話屬性
session.setAttribute("id", id);
//Enumeration header = req.getHeaderNames();
//設(shè)置請(qǐng)求字符編碼和響應(yīng)字符編碼
req.setCharacterEncoding("GB2312");
resp.setCharacterEncoding("GB2312");
resp.setHeader("content-type","text/html;charset=GB2312");
//這里是無(wú)關(guān)信息只是打印一下
String name = req.getParameter("name");
session.setAttribute("name",name );
String message = req.getParameter("message");
System.out.println(message);
//創(chuàng)建響應(yīng)對(duì)象
resp.setContentType("text/html; charset=GB2312");
PrintWriter out = resp.getWriter();
//編寫(xiě)輸出頁(yè)面
out.println("<html>");
out.println("<meta http-equiv=\"content-type\" content=\"text/html;charset=GBK\">");
out.println("<head>");
out.println("<title>guest book</title>");
out.println("</head>");
out.println("<body>");
//輸出當(dāng)前在線人數(shù)
out.println("online number:" + OnlineListener.onlineCount+"<br>");
//獲取map的鍵集的遍歷器，這里的map鍵key是會(huì)話id，值value是對(duì)應(yīng)session
Iterator<String> it = MySessionContext.getIdMap().keySet().iterator();
//利用鍵集遍歷器將創(chuàng)建的會(huì)話遍歷
while(it.hasNext()){
String sessionID = it.next();
System.out.println("Sessionid:"+sessionID);
HttpSession session1 =(HttpSession)MySessionContext.getIdMap().get(sessionID);
out.println(session1.getAttribute("createTime")+"<br>");
out.println(session1.getAttribute("name")+","+session1.getAttribute("info")+"<br><br>");
}
out.println("</body");
out.println("</html>");
out.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
System.out.println("post");
doGet(req,resp);
}
}
?當(dāng)然最后還要配置web.xml文件，主要是配置Servlet和Listener。做完后打開(kāi)tomcat，在多個(gè)瀏覽器提交表單后，最后顯示的效果如圖：
Paste_Image.png
?由于知識(shí)有限，所以寫(xiě)得很繁瑣，有待改進(jìn)
