监听器的使用：
* 作用:
* 监听作用域对象request、session、application的创建、销毁和内容的改变
* 使用:
* 创建一个实现了指定接口的java类
* 监听request--->ServletRequestListener 监听request对象的创建和销毁
* requestInitialized(ServletRequestEvent sre)//创建
* requestDestroyed(ServletRequestEvent sre)//销毁
* 注意:
* 形参可以获取监听的request对象
* sre.getServletRequest();
* 监听request--->ServletRequestAttributeListener 监听request作用域数据的变更。
attributeAdded(ServletRequestAttributeEvent srae)
* attributeRemoved(ServletRequestAttributeEvent srae)
* attributeReplaced(ServletRequestAttributeEvent srae)
* 注意：形参可以获取被监听的数据
* srae.getName() 获取监听数据的键
* srae.getValue() 获取监听数据的值
* 监听session--->HttpSessionListener 监听session的创建和销毁
* sessionCreated(HttpSessionEvent se) 创建
* sessionDestroyed(HttpSessionEvent se) 销毁
* 注意：形参可以获取被监听的session对象
* se.getSession();
* 监听session--->HttpSessionAttributeListener 监听session数据的变更
* attributeAdded(HttpSessionBindingEvent event)
* attributeRemoved(HttpSessionBindingEvent event)
* attributeReplaced(HttpSessionBindingEvent event)
* 注意:形参可以获取被监听的数据
* event.getName() 获取数据的键名
* event.getValue() 获取数据的值
* 监听application--->ServletContextListener 监听application对象的初始化和销毁
* contextInitialized(ServletContextEvent sce) 初始化 服务器启动
* contextDestroyed(ServletContextEvent sce) 销毁 服务器关闭
* 注意：
* 形参可以获取当前application对象。
* sce.getServletContext();
监听application--->ServletContextAttributeListener 监听数据的变更
attributeAdded(ServletContextAttributeEvent event)
* attributeRemoved(ServletContextAttributeEvent event)
* attributeReplaced(ServletContextAttributeEvent event)
* 注意：
* 形参可以获取当前监听的数据
* event.getName() 获取数据的键名
* event.getValue() 获取数据的值
* 在web.xml中配置监听器类
* <listener>
<listener-class>com.gs.listener.MyListener</listener-class>
</listener>
public class MyListener implements ServletRequestListener,ServletRequestAttributeListener,HttpSessionListener,HttpSessionAttributeListener,ServletContextListener,ServletContextAttributeListener{
//request对象销毁
@Override
public void requestDestroyed(ServletRequestEvent sre) {
System.out.println("我被销毁了");
}
//request对象创建
@Override
public void requestInitialized(ServletRequestEvent sre) {
System.out.println("我被创建了");
}
//监听request作用域数据的添加
@Override
public void attributeAdded(ServletRequestAttributeEvent srae) {
System.out.println("request中增加了一条数据-"+srae.getName()+":"+srae.getValue());
}
@Override
public void attributeRemoved(ServletRequestAttributeEvent srae) {
// TODO Auto-generated method stub
}
@Override
public void attributeReplaced(ServletRequestAttributeEvent srae) {
// TODO Auto-generated method stub
}
/*------------------------------------------------------------------------------*/
//监听session的创建
@Override
public void sessionCreated(HttpSessionEvent se) {
System.out.println("session被创建了");
}
//监听session的销毁
@Override
public void sessionDestroyed(HttpSessionEvent se) {
System.out.println("session被销毁了");
}
//监听session数据的表更
@Override
public void attributeAdded(HttpSessionBindingEvent event) {
System.out.println("session中增加了一条数据"+event.getName()+":"+event.getValue());
}
@Override
public void attributeRemoved(HttpSessionBindingEvent event) {
// TODO Auto-generated method stub
}
@Override
public void attributeReplaced(HttpSessionBindingEvent event) {
// TODO Auto-generated method stub
}
/*------------------------------------------------------------------------------*/
@Override
public void contextInitialized(ServletContextEvent sce) {
System.out.println("application对象被初始化了");
}
@Override
public void contextDestroyed(ServletContextEvent sce) {
System.out.println("application对象被销毁了");
}
//监听application的数据变更
@Override
public void attributeAdded(ServletContextAttributeEvent event) {
System.out.println("application中存储了数据:"+event.getName()+":"+event.getValue());
}
@Override
public void attributeRemoved(ServletContextAttributeEvent event) {
// TODO Auto-generated method stub
}
@Override
public void attributeReplaced(ServletContextAttributeEvent event) {
// TODO Auto-generated method stub
}
}
监听器统计在线人数：
package com.js.listener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MyListener implements HttpSessionListener,ServletContextListener{
//session 被创建时人数自增
@Override
public void sessionCreated(HttpSessionEvent se) {
//获取ServletContext对象
ServletContext sc = se.getSession().getServletContext();
//统计在线人数变量
int count = (int) sc.getAttribute("count");
//存储
sc.setAttribute("count", ++count);
}
//session 被销毁时人数自减
@Override
public void sessionDestroyed(HttpSessionEvent se) {
//获取ServletContext对象
ServletContext sc = se.getSession().getServletContext();
//统计在线人数变量
int count = (int) sc.getAttribute("count");
//存储
sc.setAttribute("count", --count);
}
//监听application的创建
@Override
public void contextInitialized(ServletContextEvent sce) {
ServletContext sc = sce.getServletContext();//获取application
//在application对象存储变量，统计在线人数，服务器刚启动的时候人数为0.
sc.setAttribute("count", 0);
}
//监听application的销毁
@Override
public void contextDestroyed(ServletContextEvent sce) {
}
}