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();  
                }  
            }  
        }  
    }  
  
}

　　

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原文地址：https://www.cnblogs.com/zhangyongJava/p/8297210.html