java servlet 监听_java之Servlet监听器Listener

落日映苍穹つ 2022-11-06 09:50 145阅读 0赞

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)标签与

2)一般配置在 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) \{

servlet.listener.MyListener

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：

![b2fad55d04a2e21daa40d96a50cad9eb.png][]

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：

![311479902da65816780ae3a16bde3b92.png][]

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

![0d7e25e7df1feec9f42034e456696b5e.png][]

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 map = new HashMap();

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;

servlet.listener.singleton.LoginSessionListener

(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

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();

[b2fad55d04a2e21daa40d96a50cad9eb.png]: /images/20221023/d1d7ba515b354c74a8f3a69a2739eaf8.png
[311479902da65816780ae3a16bde3b92.png]: /images/20221023/a0ade612c352451b82324f21fb788f1e.png
[0d7e25e7df1feec9f42034e456696b5e.png]: /images/20221023/555b0af16c2d4dd8af4a8e368c0526eb.png