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Servlet学习笔记（九）：监听器Listener详解
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：
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 = http://www.mamicode.com/se.getValue();>
（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();
}
}
}
}
}
Servlet学习笔记（九）：监听器Listener详解
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