J2EE中监听器Listener的应用_j2ee listner-CSDN博客

本文以二个Listener实例来讲述ServletContext、HttpSession对象生命周期及ServletContext、HttpSession对象中属性变化情况。

实例一:

用于监听ServletContext对象生命周期及ServletContext对象中属性的变化情况的监听器ContextListener,分别实现了ServletContextListener,ServletContextAttributeListener接口。代码如下:

package com.hc.znpb.servlet;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class ContextListener implements ServletContextListener,
ServletContextAttributeListener {

    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】应用被关闭!");
    }

    public void contextInitialized(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】应用被启动!");
    }

    public void attributeAdded(ServletContextAttributeEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】ServletContext对象中新增一名为" + arg0.getName()
                + "的属性,其属性值为:" + arg0.getValue());
    }

    public void attributeRemoved(ServletContextAttributeEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】ServletContext对象中一名为" + arg0.getName()
                + "的属性被删除!");
    }

    public void attributeReplaced(ServletContextAttributeEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】ServletContext对象中一名为" + arg0.getName()
                + "的属性被更新!");
    }

}

实例二:

用于监听HttpSession对象生命周期及HttpSession对象中属性的变化情况的监听器SessionListener,分别实现了HttpSessionListener,HttpSessionAttributeListener接口。代码如下:

package com.hc.znpb.servlet;

import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

import com.hc.znpb.util.SysUtil;

public class SessionListener implements HttpSessionAttributeListener,
HttpSessionListener {

// 在线人数统计
private int userCount = 0;

    public void attributeAdded(HttpSessionBindingEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】HttpSession对象中新增一名为" + arg0.getName()
                + "的属性,其属性值为" + arg0.getValue());
    }

    public void attributeRemoved(HttpSessionBindingEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】HttpSession对象中一名为" + arg0.getName()
                + "的属性被删除!");
    }

    public void attributeReplaced(HttpSessionBindingEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("【监听到】HttpSession对象中一名为" + arg0.getName()
                + "的属性被修改！");
    }

    public void sessionCreated(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub
        // 在线人数加1
        arg0.getSession().setAttribute(SysUtil.SESSION_COUNT_USERS,
                new Integer(this.userCount++));
        System.out.println("【监听到】新用户" + arg0.getSession().getId() + "上线！");
        System.out.println("【在线用户数】" + this.userCount + "人");
    }

    public void sessionDestroyed(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub
        // 在线人数减1
        arg0.getSession().setAttribute(SysUtil.SESSION_COUNT_USERS,
                new Integer(--this.userCount));
        System.out.println("【监听到】新用户" + arg0.getSession().getId() + "下线！");
        System.out.println("【在线用户数】" + this.userCount + "人");
    }