• 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
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