Listener 监听Session内的对象

Listener用于监控Session内的对象，分别是HttpSessionBindingListener与HttpSessionActivationListener。它们的触发时机分别为：

  • HttpSessionBindingListener：当对象被放到Session里时执行valueBound(HttpSessionBindingEvent event)方法。当对象被从Session里移除时执行valueUnbound(HttpSessionBingdingEvent event)方法。对象必须实现该Listener接口。
  • HttpSessionActivationListener：服务器关闭时，会将Session里的内容保存到硬盘上，这个过程叫做钝化。服务器重新启动时，会将Session内容从硬盘上重新加载。当Session里的对象被钝化时会执行sessionWillPassivate(HttpSessionEvent event)方法。当对象被重新加载时执行sessionDidActivate(HttpSessionEvent event)。对象必须实现该Listener接口。

事例如下：

package linstener;

import java.io.Serializable;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.util.Date;
import java.util.Locale;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionActivationListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class PersonInfo implements HttpSessionActivationListener,HttpSessionBindingListener,Serializable {

    

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private Log log=LogFactory.getLog(this.getClass());
    private String name;
    private Date dateCreated;

    @Override
    public void sessionDidActivate(HttpSessionEvent arg0) {
    //从硬盘恢复后被调用
        HttpSession session =arg0.getSession();
        log.info(this+"已经成功硬盘中加载。sessionid：" +session.getId());
    }

    @Override
    public void sessionWillPassivate(HttpSessionEvent arg0) {
        //即将被钝化到硬盘时调用
        HttpSession session=arg0.getSession();
        log.info(this+"即将保存到硬盘。sessionid："+session.getId());
    }

    @Override
    public void valueBound(HttpSessionBindingEvent arg0) {
        //被放入session前调用
        HttpSession session=arg0.getSession();
        String name=arg0.getName();
        log.info(this+"被绑定到session\""+session.getId()+"\"的"+name+"属性上。");
        this.setDateCreated(new Date());
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent arg0) {
        //从session 中移除后调用
        HttpSession session=arg0.getSession();
        String name=arg0.getName();
        log.info(this+"被从session\""+session.getId()+"\"的"+name+"属性上移除。");
    }

    public Date getDateCreated() {
        return dateCreated;
    }

    public void setDateCreated(Date dateCreated) {
        this.dateCreated = dateCreated;
    }
    
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "PersonInfo("+name+")";
    }
    

}

 这两个Listener监听的是Session中的对象而非Session等，因此不需要在web.xml中声明。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<jsp:directive.page import="linstener.PersonInfo" /> 
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    <%
        PersonInfo personInfo =(PersonInfo)session.getAttribute("personInfo");
        if(personInfo==null){
            personInfo=new PersonInfo();
            personInfo.setName("Alex Geng");
            session.setAttribute("personInfo", personInfo);
            out.println("PersonInfo 对象不存在。已经成功新信件。sessionId："+session.getId());
        }
        else{
            out.println("PersonInfo对象存在。无需新建。sessionId:"+session.getId());
        }
    %>
</body>
</html>

 

posted on 2017-05-02 22:50  AlexGeng  阅读(239)  评论(0)  编辑  收藏  举报

导航