09-即時統計線上人數（jsp內建對象）

最後更新：2018-12-03 來源：互聯網

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enter.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><html><body><!--建立一個使用者登入的表單，提交到doEnter頁面--><form action="doEnter.jsp" method="post">來賓名：<input type="text" name="guestName"/><br/><input type="submit" value="進入"/></form></body></html>

doEnter.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="entity.User"%><%//從請求中取出訪客名String guestName = request.getParameter("guestName");//如果來賓名稱輸入為null或者為空白，則重新登入if (guestName == null || guestName.equals("")) {response.sendRedirect("enter.jsp");} else {//建立使用者物件User user = new User();//在user對象中儲存訪客名user.setUserName(guestName);//在session中儲存User對象session.setAttribute("guest", user);response.sendRedirect("online.jsp");}%>

online.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="entity.User"%><%@page import="entity.Constents"%><body><%entity.User user = null;//判斷有沒有guest屬性if (session.getAttribute("guest") == null) {response.sendRedirect("enter.jsp");} else {user = (entity.User) session.getAttribute("guest");%>您好，<%=user.getUserName()%><br /> 此時線上人數為：<%=Constents.ONLINE_USER_COUNT%><br /><a href="doOut.jsp">離開</a><%}%></body>

doOut.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%//使用session失效session.invalidate();response.sendRedirect("enter.jsp");%>

Constents.java

package entity;public class Constents {//靜態整型變數，用來儲存線上的人數public static int ONLINE_USER_COUNT=0;//網站線上人數}

User.java

package entity;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionBindingListener;public class User implements HttpSessionBindingListener{private int id;private String userName;private String password;private String email;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}public void valueBound(HttpSessionBindingEvent event) {//存入session是自動調用Constents.ONLINE_USER_COUNT++;}public void valueUnbound(HttpSessionBindingEvent event) {//從session中刪除自動調用Constents.ONLINE_USER_COUNT--;}}

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