首先我需要一個能訪問網站人數的功能，那莫具體來講就是需要一個能全局存儲的，在 java web 中 爲啥不用session 因爲他代表的試一次會話是一種局部存儲， 所以用 servletContext 存儲更加合適因爲他是全局的， 可以實現ServletContextListener 接口重寫裏面的2個方法
如果你沒懂我說的他們之前區別可以看看
http://www.cnblogs.com/javadu/archive/2011/11/25/2263799.html
http://www.cnblogs.com/javadu/archive/2011/11/25/2263808.html
contextDestroyed(ServletContextEvent arg0)
contextInitialized(ServletContextEvent arg0)
在初始化中可以讀取我存儲在磁盤文件那個文件獲取個數 因爲如果不存儲的話 服務器停止他也會沒有了
在銷燬的方法中我可以拿到存儲在servletcontext中的個數並存儲在文件中，這樣就可以實現存儲保存了
當然這邊的方法是多種的你願意存儲在哪就存在哪，數據庫 其他都可以
廢話了那莫多開始 coding 吧
首先自定義一個我自己的監聽器，然後重寫2個方法，銷燬的方法中是存儲在磁盤的路徑你可以任意指定，但是你存儲在WEN-INF/classes 中他會報沒有訪問權限的錯誤
package com.listener;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class MyListener implements ServletContextListener {
@Override
public void contextDestroyed(ServletContextEvent arg0) {
// TODO Auto-generated method stub
System.out.println("推出");
ServletContext sc = arg0.getServletContext();
Counter counter = (Counter) sc.getAttribute("counter");
if(counter!=null) {
//String filepath = s
try {
// BufferedWriter bw = new BufferedWriter(new OutputStreamWriter())
// PrintWriter pw = new PrintWriter("/count.txt");
PrintWriter pw = new PrintWriter(new OutputStreamWriter(new FileOutputStream("D:\\develop\\apache-tomcat-7.0.67\\webapps\\test\\WEB-INF\\classes\\count.txt")));
pw.println(counter.getCounter());
pw.flush();
pw.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
@Override
public void contextInitialized(ServletContextEvent arg0) {
// TODO Auto-generated method stub
System.out.println("進入");
ServletContext sc = arg0.getServletContext();
System.out.println(sc.getResourceAsStream("/WEB-INF/classes/count.txt"));
BufferedReader br = new BufferedReader(new InputStreamReader(sc.getResourceAsStream("/WEB-INF/classes/count.txt")));
try {
int count = Integer.parseInt((br.readLine()));
br.close();
sc.setAttribute("counter", new Counter(count));
} catch (NumberFormatException | IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
然後就是頁面了
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8" import="com.listener.*"%>
<!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>
<%
Counter count = (Counter) this.getServletContext().getAttribute("counter");
count.setCounter(count.getCounter() + 1);
this.getServletContext().setAttribute("counter", count);
%>
<%=count.getCounter()%>
</body>
</html>實體類
package com.listener;
public class Counter {
private int counter;
public void setCounter(int counter) {
this.counter = counter;
}
public int getCounter() {
return counter;
}
public Counter(int counter) {
// TODO Auto-generated constructor stub
this.counter = counter;
}
}
最後不要忘了在web.xml 中配置listener 中讓我們自定義的起作用
<?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" xmlns:web="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_2_5.xsd" id="WebApp_ID" version="2.5">
<listener>
<listener-class>com.listener.MyListener</listener-class>
</listener>
<display-name>Archetype Created Web Application</display-name>
</web-app>