实现监听电脑的动作，实现一个监听器的接口（N种）
1.实现一个监听器接口
package com.kuang.listener;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class OnLineCountListener implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
Integer onLineCount = (Integer) servletContext.getAttribute("onLineCount");
if (onLineCount == null){
onLineCount = new Integer(1);
}else{
onLineCount = new Integer(onLineCount + 1);
}
servletContext.setAttribute("onLineCount",onLineCount);
}
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
Integer onLineCount = (Integer) servletContext.getAttribute("onLineCount");
if (onLineCount == null){
onLineCount = new Integer(0);
}else{
onLineCount = new Integer(onLineCount - 1);
}
servletContext.setAttribute("onLineCount",onLineCount);
httpSessionEvent.getSession().invalidate();
}
}
2.配置监听器web.xml
com.kuang.listener.OnLineCountListener
3.页面验证
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
$Title$
当前共有<%=this.getServletConfig().getServletContext().getAttribute("onLineCount")%>人访问
