实现一个监听器的接口；
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编写一个监听器
实现监听器的接口…
package Java.Listener;import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;//统计在线人数
public class OnlineCountListener implements HttpSessionListener {//创建session监听： 看你的一举一动//一旦创建Session就会触发一次这个事件！@Overridepublic void sessionCreated(HttpSessionEvent se) {ServletContext context= se.getSession().getServletContext();Integer OnlineCount= (Integer) context.getAttribute("OnlineCount");if (OnlineCount==null){OnlineCount = new Integer(1);}else {int count = OnlineCount.intValue();OnlineCount = new Integer(count+1);}context.setAttribute("OnlineCount",OnlineCount);}//销毁session监听//一旦销毁Session就会触发一次这个事件！@Overridepublic void sessionDestroyed(HttpSessionEvent se) {ServletContext ctx = se.getSession().getServletContext();Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");if (onlineCount==null){onlineCount = new Integer(0);}else {int count = onlineCount.intValue();onlineCount = new Integer(count-1);}ctx.setAttribute("OnlineCount",onlineCount);}
}
2.配置XML
<listener><listener-class>Java.Listener.OnlineCountListener</listener-class></listener>4.配置前端页面
<html>
<body>
<h2>Hello World!</h2><h1> 当前在线人数<span><%=this.getServletConfig().getServletContext().getAttribute("OnlineCount")%></span>
</h1>
</body>
</html>