ServletContextListener(Listener机制)

Listener可以监听服务器端的相关状态变化，当服务器状态发生改变，将调用相应的Listener

这种机制可以成为回调机制，ServletContextListener配置如下

web.xml

<listener>
  <listener-class>com.hugui.drp.util.listener.InitListener</listener-class>
 </listener>

InitListener.java(在tomcat启动时就会被初始化)

package com.hugui.drp.util.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import com.hugui.drp.util.BeanFactory;
import com.hugui.drp.util.Constants;

/**
 * 采用ServletContextListener完成初始化
 * @author Administrator
 *
 */
public class InitListener implements ServletContextListener {

 public void contextDestroyed(ServletContextEvent arg0) {
  

 }

 public void contextInitialized(ServletContextEvent sce) {
  System.out.println("创建系统的BeanFactory...");
  //将抽象工厂放到ServletContext中
  BeanFactory beanFactory = BeanFactory.getInstance();
  sce.getServletContext().setAttribute("beanFactory", beanFactory);
  
  //加入常量
  sce.getServletContext().setAttribute("add", Constants.ADD);
  sce.getServletContext().setAttribute("del", Constants.DEL);
  sce.getServletContext().setAttribute("modify", Constants.MODIFY);
  sce.getServletContext().setAttribute("showAdd", Constants.SHOW_ADD);
  sce.getServletContext().setAttribute("query", Constants.QUERY);
  sce.getServletContext().setAttribute("audit", Constants.AUDIT);

 }

}
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另外还有HttpSessionListener

Method Summary

void	sessionCreated(HttpSessionEvent se) //当session被创建时调用，如jsp页面（session=true）打开时           Notification that a session was created.
void	sessionDestroyed(HttpSessionEvent se)           Notification that a session is about to be invalidated.

 HttpSessionAttributeListener(session的东西发生改变时：如往session里面添加东西)

Method Summary

void	attributeAdded(HttpSessionBindingEvent se) //session.serAttribute("user");           Notification that an attribute has been added to a session.
void	attributeRemoved(HttpSessionBindingEvent se)  //如session.removeAttribute("user");           Notification that an attribute has been removed from a session.
void	attributeReplaced(HttpSessionBindingEvent se)           Notification that an attribute has been replaced in a session.

HttpSessionBindingEvent

Method Summary

String	getName() //能得到session的名字           Returns the name with which the attribute is bound to or unbound from the session.
HttpSession	getSession()           Return the session that changed.
Object	getValue() //得到session的值           Returns the value of the attribute that has been added, removed or replaced.