JavaWeb中的application统计在线人数案例
1、后台部分（a/登录，建一个LoginServlet类继承HttpServlet父类）
package com.iotek.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class LoginServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
ServletContext application = req.getServletContext();
Integer count = (Integer)application.getAttribute("count");
if(count==null){
application.setAttribute("count", 1);
}else{
application.setAttribute("count", count+1);
}
resp.sendRedirect("index.jsp");
}
}<pre name="code" class="java">（b/注销，建一个LogoutServlet类继承HttpServlet父类）
2、前端部分代码
<pre name="code" class="javascript"><%@page import="org.apache.catalina.SessionListener"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8" %>
<!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=utf-8">
<title>Insert title here</title>
</head>
<body>
当前在线人数：
<%
Object obj=application.getAttribute("count");
%>
<%
if(obj==null){
out.print(0);
}else{
out.println(obj);
}
%>
<form action="baidu" method="GET">
<input type="submit" value="登录"/>
</form>
<form action="baidu2" method="GET">
<input type="submit" value="注销"/>
</form>
</body>
</html>3、web.xml的配置
<pre name="code" class="javascript"><?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>demo1103</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.htm</welcome-file>
<welcome-file>index.jsp</welcome-file>
<welcome-file>default.html</welcome-file>
<welcome-file>default.htm</welcome-file>
<welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>test</servlet-name>
<servlet-class>com.iotek.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>test</servlet-name>
<url-pattern>/baidu</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>test2</servlet-name>
<servlet-class>com.iotek.servlet.LogoutServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>test2</servlet-name>
<url-pattern>/baidu2</url-pattern>
</servlet-mapping>
</web-app>4、application
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