12 监听器
实现一个监听器的接口
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编写一个监听器
package com.karl.listener; import javax.servlet.ServletContext; import javax.servlet.http.HttpSessionEvent; import javax.servlet.http.HttpSessionListener; //统计网站在线人数: 统计session public class OnlineCountListener implements HttpSessionListener { @Override //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! public void sessionCreated(HttpSessionEvent httpSessionEvent) { ServletContext servletContext = httpSessionEvent.getSession().getServletContext(); Integer onlineCount = (Integer)servletContext.getAttribute("OnlineCount"); if (null == onlineCount){ onlineCount = 1; }else { int count = onlineCount; onlineCount = count + 1; } servletContext.setAttribute("OnlineCount", onlineCount); } @Override //销毁session监听 //一旦销毁Session就会触发一次这个事件! public void sessionDestroyed(HttpSessionEvent httpSessionEvent) { } } -
web.xml中配置监听器
<listener> <listener-class>com.karl.listener.OnlineCountListener</listener-class> </listener> 看情况使用
