java之Servlet监听器Listener

常用应用场景:单点登录、统计在线人数

一、简介

（一）概述

1、Listener 用于监听 java web程序中的事件，例如创建、修改、删除Session、request、context等，并触发响应的事件。

2、 Listener 对应观察者模式，事件发生的时候会自动触发该事件对应的Listeer。 Listener 主要用于对 Session、request、context 进行监控。servlet2.5 规范中共有 8 种Listener  。

（二）实现

1、不同功能的Listener 需要实现不同的 Listener  接口，一个Listener也可以实现多个接口，这样就可以多种功能的监听器一起工作。

2、8种监听器可以分为三类：

1）监听 Session、request、context 的创建于销毁，分别为

HttpSessionLister、ServletContextListener、ServletRequestListener

2）监听对象属性变化，分别为：

HttpSessionAttributeLister、ServletContextAttributeListener、ServletRequestAttributeListener

3）监听Session 内的对象，分别为HttpSessionBindingListener 和 HttpSessionActivationListener。与上面六类不同，这两类 Listener 监听的是Session 内的对象，而非 Session 本身，不需要在 web.xml中配置。

2、实现web.xml的Listener配置。

1）<listener>标签与 <listener-class>

2）<listener>一般配置在 <servlet>便签的前面。

package servlet.listener;  

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
/**
 *
 * MyListener.java
 *
 * @title Context监听器
 * @description
 * @author SAM-SHO
 * @Date 2014-9-25
 */
public class MyListener implements ServletContextListener {  

    public void contextDestroyed(ServletContextEvent sce) {  

    }  

    public void contextInitialized(ServletContextEvent sce) {  

    }  

}

　　

<!--监听器 -->
<listener>
    <listener-class>servlet.listener.MyListener</listener-class>
</listener> 

二、八种类型监听器

（一）监听 Session、request、context 的创建于销毁。

HttpSessionLister、ServletContextListener、ServletRequestListener

1、三种监听器的触发时机及使用：

2、实例：实现监听对象的创建与销毁

package servlet.listener;  

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;  

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

/**
 *
 * ListenerTest.java
 *
 * @title 监听对象的创建与销毁
 * @description
 * @author SAM-SHO
 * @Date 2014-12-10
 */
public class ListenerTest implements HttpSessionListener, ServletContextListener, ServletRequestListener {  

    Log log = LogFactory.getLog(getClass());  

    // 创建 session
    public void sessionCreated(HttpSessionEvent se) {
        HttpSession session = se.getSession();
        log.info("新创建一个session, ID为: " + session.getId());
    }  

    // 销毁 session
    public void sessionDestroyed(HttpSessionEvent se) {
        HttpSession session = se.getSession();
        log.info("销毁一个session, ID为: " + session.getId());
    }  

    // 加载 context
    public void contextInitialized(ServletContextEvent sce) {
        ServletContext servletContext = sce.getServletContext();
        log.info("即将启动" + servletContext.getContextPath());
    }  

    // 卸载 context
    public void contextDestroyed(ServletContextEvent sce) {
        ServletContext servletContext = sce.getServletContext();
        log.info("即将关闭" + servletContext.getContextPath());
    }  

    // 创建 request
    public void requestInitialized(ServletRequestEvent sre) {  

        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();  

        String uri = request.getRequestURI();
        uri = request.getQueryString() == null ? uri : (uri + "?" + request.getQueryString());  

        request.setAttribute("dateCreated", System.currentTimeMillis());  

        log.info("IP " + request.getRemoteAddr() + " 请求 " + uri);
    }  

    // 销毁 request
    public void requestDestroyed(ServletRequestEvent sre) {  

        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();  

        long time = System.currentTimeMillis() - (Long) request.getAttribute("dateCreated");  

        log.info(request.getRemoteAddr() + "请求处理结束, 用时" + time + "毫秒. ");
    }  

}

　　

（二）监听对象属性变化，分别为HttpSessionAttributeLister、ServletContextAttributeListener、ServletRequestAttributeListener

1、三种监听器的触发时机及使用：

2、实例：实现对象属性的监听

package servlet.listener;  

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;  

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
 *
 * SessionAttributeListenerTest.java
 *
 * @title 监听Session对象的属性
 * @description
 * @author SAM-SHO
 * @Date 2014-12-10
 */
public class SessionAttributeListenerTest implements HttpSessionAttributeListener {  

    Log log = LogFactory.getLog(getClass());  

    // 添加属性
    public void attributeAdded(HttpSessionBindingEvent se) {
        HttpSession session = se.getSession();
        String name = se.getName();
        log.info("新建session属性：" + name + ", 值为：" + se.getValue());
    }  

    // 删除属性
    public void attributeRemoved(HttpSessionBindingEvent se) {
        HttpSession session = se.getSession();
        String name = se.getName();
        log.info("删除session属性：" + name + ", 值为：" + se.getValue());
    }  

    // 修改属性
    public void attributeReplaced(HttpSessionBindingEvent se) {
        HttpSession session = se.getSession();
        String name = se.getName();
        Object oldValue = se.getValue();
        log.info("修改session属性：" + name + ", 原值：" + oldValue + ", 新值：" + session.getAttribute(name));
    }
}

　　

（三）监听Session 内的对象，分别为HttpSessionBindingListener 和 HttpSessionActivationListener

1、触发时机及使用：对象必须实现Listener接口，不需要在web.xml中配置

2、实例：实现对象属性的监听

package servlet.listener;  

import java.io.Serializable;
import java.util.Date;  

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;
/**
 *
 * PersonInfo.java
 *
 * @title 同时实现多个接口
 * 被串行化，需要实现Serializable接口
 * @description
 * @author SAM-SHO
 * @Date 2014-12-10
 */
public class PersonInfo implements HttpSessionActivationListener, HttpSessionBindingListener, Serializable {  

    private static final long serialVersionUID = -4780592776386225973L;  

    Log log = LogFactory.getLog(getClass());  

    private String name;
    private Date dateCreated;  

    // 从硬盘加载后
    public void sessionDidActivate(HttpSessionEvent se) {
        HttpSession session = se.getSession();
        log.info(this + "已经成功从硬盘中加载。sessionId: " + session.getId());
    }  

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

    // 被放进session前
    public void valueBound(HttpSessionBindingEvent event) {
        HttpSession session = event.getSession();
        String name = event.getName();
        log.info(this + "被绑定到session \"" + session.getId() + "\"的" + name + "属性上");  

        // 记录放到session中的时间
        this.setDateCreated(new Date());
    }  

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

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

    public String getName() {
        return name;
    }  

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

    public Date getDateCreated() {
        return dateCreated;
    }  

    public void setDateCreated(Date dateCreated) {
        this.dateCreated = dateCreated;
    }  

}

　　

三、Listener 实例

（一）单态登录：一个账号只能在一台机器上登录。

1、Listener 的代码：

package servlet.listener.singleton;  

import java.util.HashMap;
import java.util.Map;  

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;  

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

/**
 *
 * LoginSessionListener.java
 *
 * @title 实现单态登录的监听器
 * @description
 * @author SAM-SHO
 * @Date 2014-12-10
 */
public class LoginSessionListener implements HttpSessionAttributeListener {  

    Log log = LogFactory.getLog(this.getClass());  

    Map<String, HttpSession> map = new HashMap<String, HttpSession>();  

    public void attributeAdded(HttpSessionBindingEvent event) {  

        String name = event.getName();  

        // 登录
        if (name.equals("personInfo")) {  

            PersonInfo personInfo = (PersonInfo) event.getValue();  

            if (map.get(personInfo.getAccount()) != null) {  

                // map 中有记录，表明该帐号在其他机器上登录过，将以前的登录失效
                HttpSession session = map.get(personInfo.getAccount());
                PersonInfo oldPersonInfo = (PersonInfo) session.getAttribute("personInfo");//map已经存在的旧的信息  

                log.info("帐号" + oldPersonInfo.getAccount() + "在" + oldPersonInfo.getIp() + "已经登录，该登录将被迫下线。");  

                session.removeAttribute("personInfo");
                session.setAttribute("msg", "您的帐号已经在其他机器上登录，您被迫下线。");
            }  

            // 将session以用户名为索引，放入map中
            map.put(personInfo.getAccount(), event.getSession());
            log.info("帐号" + personInfo.getAccount() + "在" + personInfo.getIp() + "登录。");
        }
    }  

    public void attributeRemoved(HttpSessionBindingEvent event) {  

        String name = event.getName();  

        // 注销
        if (name.equals("personInfo")) {
            // 将该session从map中移除
            PersonInfo personInfo = (PersonInfo) event.getValue();
            map.remove(personInfo.getAccount());
            log.info("帐号" + personInfo.getAccount() + "注销。");
        }
    }  

    public void attributeReplaced(HttpSessionBindingEvent event) {  

        String name = event.getName();  

        // 没有注销的情况下，用另一个帐号登录
        if (name.equals("personInfo")) {  

            // 移除旧的的登录信息
            PersonInfo oldPersonInfo = (PersonInfo) event.getValue();
            map.remove(oldPersonInfo.getAccount());  

            // 新的登录信息
            PersonInfo personInfo = (PersonInfo) event.getSession().getAttribute("personInfo");  

            // 也要检查新登录的帐号是否在别的机器上登录过
            if (map.get(personInfo.getAccount()) != null) {
                // map 中有记录，表明该帐号在其他机器上登录过，将以前的登录失效
                HttpSession session = map.get(personInfo.getAccount());
                session.removeAttribute("personInfo");
                session.setAttribute("msg", "您的帐号已经在其他机器上登录，您被迫下线。");
            }
            map.put("personInfo", event.getSession());
        }  

    }  

}

　　

package servlet.listener.singleton;  

import java.io.Serializable;
import java.util.Date;  

/**
 *
 * PersonInfo.java
 *
 * @title
 * @description
 * @author SAM-SHO
 * @Date 2014-12-10
 */
public class PersonInfo implements Serializable {  

    private static final long serialVersionUID = 4063725584941336123L;  

    // 帐号
    private String account;  

    // 登录IP地址
    private String ip;  

    // 登录时间
    private Date loginDate;  

    public String getAccount() {
        return account;
    }  

    public void setAccount(String account) {
        this.account = account;
    }  

    public String getIp() {
        return ip;
    }  

    public void setIp(String ip) {
        this.ip = ip;
    }  

    public Date getLoginDate() {
        return loginDate;
    }  

    public void setLoginDate(Date loginDate) {
        this.loginDate = loginDate;
    }  

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((account == null) ? 0 : account.hashCode());
        result = prime * result + ((ip == null) ? 0 : ip.hashCode());
        return result;
    }  

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        PersonInfo other = (PersonInfo) obj;
        if (account == null) {
            if (other.account != null)
                return false;
        } else if (!account.equals(other.account))
            return false;
        if (ip == null) {
            if (other.ip != null)
                return false;
        } else if (!ip.equals(other.ip))
            return false;
        return true;
    }  

}

　　

<!-- 单态登录监听器 -->
<listener>
    <listener-class>servlet.listener.singleton.LoginSessionListener</listener-class>
</listener>

　　

（二）显示在线人数：会需要3个监听器。

1、ContextListener：获取服务启动的时间等。

2、RequestListener：获取客户端的IP、访问地址，访问次数等。

3、SessionListener：需要监听 Session 的创建与属性变化。

4、代码如下：

　　

package com.helloweenvsfei.listener;  

import java.util.Date;  

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

import com.helloweenvsfei.util.ApplicationConstants;  

public class MyContextListener implements ServletContextListener {  

    public void contextInitialized(ServletContextEvent event) {
        // 启动时，记录服务器启动时间
        ApplicationConstants.START_DATE = new Date();
    }  

    public void contextDestroyed(ServletContextEvent event) {
        // 关闭时，将结果清除。也可以将结果保存到硬盘上。
        ApplicationConstants.START_DATE = null;
        ApplicationConstants.MAX_ONLINE_COUNT_DATE = null;
    }
}

　　

package com.helloweenvsfei.listener;  

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;  

public class MyRequestListener implements ServletRequestListener {  

    public void requestDestroyed(ServletRequestEvent event) {
    }  

    public void requestInitialized(ServletRequestEvent event) {  

        HttpServletRequest request = (HttpServletRequest) event
                .getServletRequest();  

        HttpSession session = request.getSession(true);  

        // 记录IP地址
        session.setAttribute("ip", request.getRemoteAddr());  

        // 记录访问次数，只记录访问 .html, .do, .jsp, .action 的累计次数
        String uri = request.getRequestURI();
        String[] suffix = { ".html", ".do", ".jsp", ".action" };
        for (int i=0; i<suffix.length; i++) {
            if (uri.endsWith(suffix[i])) {
                break;
            }
            if(i == suffix.length-1)
                return;
        }  

        Integer activeTimes = (Integer) session.getAttribute("activeTimes");  

        if (activeTimes == null) {
            activeTimes = 0;
        }  

        session.setAttribute("activeTimes", activeTimes + 1);
    }
}

　　

package com.helloweenvsfei.listener;  

import java.util.Date;  

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

import com.helloweenvsfei.util.ApplicationConstants;  

public class MySessionListener implements HttpSessionListener,
        HttpSessionAttributeListener {  

    public void sessionCreated(HttpSessionEvent sessionEvent) {  

        HttpSession session = sessionEvent.getSession();  

        // 将 session 放入 map
        ApplicationConstants.SESSION_MAP.put(session.getId(), session);
        // 总访问人数++
        ApplicationConstants.TOTAL_HISTORY_COUNT++;  

        // 如果当前在线人数超过历史记录，则更新最大在线人数，并记录时间
        if (ApplicationConstants.SESSION_MAP.size() > ApplicationConstants.MAX_ONLINE_COUNT) {
            ApplicationConstants.MAX_ONLINE_COUNT = ApplicationConstants.SESSION_MAP
                    .size();
            ApplicationConstants.MAX_ONLINE_COUNT_DATE = new Date();
        }
    }  

    public void sessionDestroyed(HttpSessionEvent sessionEvent) {
        HttpSession session = sessionEvent.getSession();
        // 将session从map中移除
        ApplicationConstants.SESSION_MAP.remove(session.getId());
    }  

    public void attributeAdded(HttpSessionBindingEvent event) {  

        if (event.getName().equals("personInfo")) {  

            // 当前登录用户数++
            ApplicationConstants.CURRENT_LOGIN_COUNT++;
            HttpSession session = event.getSession();  

            // 查找该帐号有没有在其他机器上登录
            for (HttpSession sess : ApplicationConstants.SESSION_MAP.values()) {  

                // 如果该帐号已经在其他机器上登录，则以前的登录失效
                if (event.getValue().equals(sess.getAttribute("personInfo"))
                        && session.getId() != sess.getId()) {
                    sess.invalidate();
                }
            }
        }
    }  

    public void attributeRemoved(HttpSessionBindingEvent event) {  

        // 注销 当前登录用户数--
        if (event.getName().equals("personInfo")) {
            ApplicationConstants.CURRENT_LOGIN_COUNT--;
        }
    }  

    public void attributeReplaced(HttpSessionBindingEvent event) {  

        // 重新登录
        if (event.getName().equals("personInfo")) {
            HttpSession session = event.getSession();
            for (HttpSession sess : ApplicationConstants.SESSION_MAP.values()) {
                // 如果新帐号在其他机器上登录过，则以前登录失效
                if (event.getValue().equals(sess.getAttribute("personInfo"))
                        && session.getId() != sess.getId()) {
                    sess.invalidate();
                }
            }
        }
    }  

}