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) {
}
}
原文地址：https://www.cnblogs.com/gshao/p/10358050.html
时间： 2024-08-30 04:09:14