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Java web----监听器

时间:2015-01-15 20:20:05      阅读:176      评论:0      收藏:0      [点我收藏+]

标签:java web   监听器   

1 JavaWeb监听器概述

在JavaWeb被监听的事件源为:ServletContext、HttpSession、ServletRequest,即三大域对象。

  • 监听域对象“创建”与“销毁”的监听器;
  • 监听域对象“操作域属性”的监听器;
  • 监听HttpSession的监听器。

2 创建与销毁监听器

创建与销毁监听器一共有三个:

ServletContextListener:Tomcat启动和关闭时调用下面两个方法

  • public void contextInitialized(ServletContextEvent evt):ServletContext对象被创建后调用;
  • public void contextDestroyed(ServletContextEvent evt):ServletContext对象被销毁前调用;

HttpSessionListener:开始会话和结束会话时调用下面两个方法

  • public void sessionCreated(HttpSessionEvent evt):HttpSession对象被创建后调用;
  • public void sessionDestroyed(HttpSessionEvent evt):HttpSession对象被销毁前调用;

ServletRequestListener:开始请求和结束请求时调用下面两个方法

  • public void requestInitiallized(ServletRequestEvent evt):ServletRequest对象被创建后调用;
  • public void requestDestroyed(ServletRequestEvent evt):ServletRequest对象被销毁前调用。

3 事件对象

ServletContextEvent:ServletContextgetServletContext();

HttpSeessionEvent:HttpSessiongetSession();

ServletRequestEvent:

  • ServletRequest getServletRequest()
  • ServletContext getServletContext()

编写测试例子:

  • 编写MyServletContextListener类,实现ServletContextListener接口;
  • 在web.xml文件中部署监听器;
  • 为了看到session销毁的效果,在web.xml文件中设置session失效时间为1分钟;

/*
 * ServletContextListener实现类
 * contextDestroyed() -- 在ServletContext对象被销毁前调用
 * contextInitialized() --  -- 在ServletContext对象被创建后调用
 * ServletContextEvent -- 事件类对象
 *     该类有getServletContext(),用来获取ServletContext对象,即获取事件源对象
 */
public class MyServletContextListener implements ServletContextListener {
	public void contextDestroyed(ServletContextEvent evt) {
		System.out.println("销毁ServletContext对象");
	}

	public void contextInitialized(ServletContextEvent evt) {
		System.out.println("创建ServletContext对象");
	}
}

/*
 * HttpSessionListener实现类
 * sessionCreated() -- 在HttpSession对象被创建后被调用
 * sessionDestroyed() --  -- 在HttpSession对象被销毁前调用
 * HttpSessionEvent -- 事件类对象
 *     该类有getSession(),用来获取当前HttpSession对象,即获取事件源对象
 */
public class MyHttpSessionListener implements HttpSessionListener {
	public void sessionCreated(HttpSessionEvent evt) {
		System.out.println("创建session对象");
	}

	public void sessionDestroyed(HttpSessionEvent evt) {
		System.out.println("销毁session对象");
	}
}

/*
 * ServletRequestListener实现类
 * requestDestroyed() -- 在ServletRequest对象被销毁前调用
 * requestInitialized() -- 在ServletRequest对象被创建后调用
 * ServletRequestEvent -- 事件类对象
 *     该类有getServletContext(),用来获取ServletContext对象
 *     该类有getServletRequest(),用来获取当前ServletRequest对象,即事件源对象
 */
public class MyServletRequestListener implements ServletRequestListener {
	public void requestDestroyed(ServletRequestEvent evt) {
		System.out.println("销毁request对象");
	}

	public void requestInitialized(ServletRequestEvent evt) {
		System.out.println("创建request对象");
	}
}

<listener>
<listener-class>cn.itcast.listener.MyServletContextListener</listener-class>
</listener>
<listener>
<listener-class>cn.itcast.listener.MyHttpSessionListener</listener-class>
</listener>
<listener>
<listener-class>cn.itcast.listener.MyServletRequestListener</listener-class>
</listener>
<session-config>
 <session-timeout>1</session-timeout>
</session-config>

4 操作域属性的监听器

当对域属性进行增、删、改时,执行的监听器一共有三个:

ServletContextAttributeListener:在ServletContext域进行增、删、改属性时调用下面方法。

  • public void attributeAdded(ServletContextAttributeEvent evt)
  • public void attributeRemoved(ServletContextAttributeEvent evt)
  • public void attributeReplaced(ServletContextAttributeEvent evt)

HttpSessionAttributeListener:在HttpSession域进行增、删、改属性时调用下面方法

  • public void attributeAdded(HttpSessionBindingEvent evt)
  • public void attributeRemoved (HttpSessionBindingEvent evt)
  • public void attributeReplaced (HttpSessionBindingEvent evt)

ServletRequestAttributeListener:在ServletRequest域进行增、删、改属性时调用下面方法

  • public void attributeAdded(ServletRequestAttributeEvent evt)
  • public void attributeRemoved (ServletRequestAttributeEvent evt)
  • public void attributeReplaced (ServletRequestAttributeEvent evt)

下面对这三个监听器的事件对象功能进行介绍:

ServletContextAttributeEvent

  • String getName():获取当前操作的属性名;
  • Object getValue():获取当前操作的属性值;
  • ServletContext getServletContext():获取ServletContext对象。

HttpSessionBindingEvent

  • String getName():获取当前操作的属性名;
  • Object getValue():获取当前操作的属性值;
  • HttpSession getSession():获取当前操作的session对象。

ServletRequestAttributeEvent

  • String getName():获取当前操作的属性名;
  • Object getValue():获取当前操作的属性值;
  • ServletContext getServletContext():获取ServletContext对象;
  • ServletRequest getServletRequest():获取当前操作的ServletRequest对象。

package com.cug.attribute01;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;

public class MyServletContextAttributeListener implements ServletContextAttributeListener{

	@Override
	public void attributeAdded(ServletContextAttributeEvent arg0) {
		System.out.println("attributeAdded:"+arg0.getName()+",\n"+arg0.getValue());
	}

	@Override
	public void attributeRemoved(ServletContextAttributeEvent arg0) {
		System.out.println("attributeRemoved:"+arg0.getName()+","+arg0.getValue());
	}

	@Override
	public void attributeReplaced(ServletContextAttributeEvent arg0) {
		//arg0.getValue()为替代之前的值
		//arg0.getServletContext().getAttribute(arg0.getName())为替代之后的值
		System.out.println("attributeReplaced:"+arg0.getName()+","+arg0.getValue()
				+","+arg0.getServletContext().getAttribute(arg0.getName()));
	}

}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'index.jsp' starting page</title>
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->
  </head>
  
  <body>
    <%
    	application.setAttribute("xxx", "aaa");
    %>
  </body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'replace.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
  <%
    application.setAttribute("xxx","bbb");
  %>
  </body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'remove.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
  <%
    application.removeAttribute("xxx");
  %>
  </body>
</html>

5 HttpSession的监听器

还有两个与HttpSession相关的特殊的监听器,这两个监听器的特点如下:

  • 不用在web.xml文件中部署;
  • 这两个监听器不是给session添加,而是给Bean添加。即让Bean类实现监听器接口,然后再把Bean对象添加到session域中。

下面对这两个监听器介绍一下:

HttpSessionBindingListener:当某个类实现了该接口后,可以感知本类对象添加到session中,以及感知从session中移除。例如让Person类实现HttpSessionBindingListener接口,那么当把Person对象添加到session中,或者把Person对象从session中移除时会调用下面两个方法:

  • public void valueBound(HttpSessionBindingEvent event):当把监听器对象添加到session中会调用监听器对象的本方法;
  • public void valueUnbound(HttpSessionBindingEvent event):当把监听器对象从session中移除时会调用监听器对象的本方法;

这里要注意,HttpSessionBindingListener监听器的使用与前面介绍的都不相同,当该监听器对象添加到session中,或把该监听器对象从session移除时会调用监听器中的方法。并且无需在web.xml文件中部署这个监听器。

package com.cug.session;

import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class Person implements HttpSessionBindingListener{
	private String name;
	private int age;
	private String sex;
	public Person() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Person(String name, int age, String sex) {
		super();
		this.name = name;
		this.age = age;
		this.sex = sex;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", sex=" + sex + "]";
	}
	@Override
	public void valueBound(HttpSessionBindingEvent arg0) {
		System.out.println("valueBound~");
	}
	@Override
	public void valueUnbound(HttpSessionBindingEvent arg0) {
		System.out.println("valueUnbound~");
	}
	
	
}

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'a.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
    <%
    	com.cug.session.Person per = new com.cug.session.Person("zhu",23,"男");
    	session.setAttribute("person", per);
    %>
  </body>
</html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'b.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
    <%
    	out.println(session.getAttribute("person"));
    %>
  </body>
</html>

6 HttpSession的监听器

HttpSessionActivationListener:Tomcat会在session从时间不被使用时钝化session对象,所谓钝化session,就是把session通过序列化的方式保存到硬盘文件中。当用户再使用session时,Tomcat还会把钝化的对象再活化session,所谓活化就是把硬盘文件中的session在反序列化回内存。当session被Tomcat钝化时,session中存储的对象也被纯化,当session被活化时,也会把session中存储的对象活化。如果某个类实现了HttpSessionActiveationListener接口后,当对象随着session被钝化和活化时,下面两个方法就会被调用:

  • public void sessionWillPassivate(HttpSessionEvent se):当对象感知被钝化时调用本方法;
  • public void sessionDidActivate(HttpSessionEvent se):当对象感知被活化时调用本方法;

HttpSessionActivationListener监听器与HttpSessionBindingListener监听器相似,都是感知型的监听器,例如让Person类实现了HttpSessionActivationListener监听器接口,并把Person对象添加到了session中后,当Tomcat钝化session时,同时也会钝化session中的Person对象,这时Person对象就会感知到自己被钝化了,其实就是调用Person对象的sessionWillPassivate()方法。当用户再次使用session时,Tomcat会活化session,这时Person会感知到自己被活化,其实就是调用Person对象的sessionDidActivate()方法。

注意,因为钝化和活化session,其实就是使用序列化和反序列化技术把session从内存保存到硬盘,和把session从硬盘加载到内存。这说明如果Person类没有实现Serializable接口,那么当session钝化时就不会钝化Person,而是把Person从session中移除再钝化!这也说明session活化后,session中就不在有Person对象了。

示例步骤:

先不管HttpSessionActivationListener监听器接口,先来配置Tomcat钝化session的参数,把下面配置文件放到tomcat\conf\catalina\localhost目录下!文件名称为项目名称。

<Context>
	<Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1">
		<Store className="org.apache.catalina.session.FileStore" directory="mysession"/>
	</Manager>
</Context>

访问项目的index.jsp页面,这会使Tomcat创建Session对象,然后等待一分钟后,查看Tomcat\work\Catalina\localhost\listener\mysession目录下是否会产生文件,如果产生了,说明钝化session的配置成功了,可以开始下一步了。

创建Person类,让Person类实现HttpSessionActivationListener和Serializable接口:

public class Person implements HttpSessionActivationListener, Serializable {
	private String name;
	private int age;
	private String sex;
	
	public Person(String name, int age, String sex) {
		super();
		this.name = name;
		this.age = age;
		this.sex = sex;
	}

	public Person() {
		super();
	}

	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", sex=" + sex + "]";
	}

	public String getName() {
		return name;
	}

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

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public void sessionDidActivate(HttpSessionEvent evt) {
		System.out.println("session已经活化");
	}

	public void sessionWillPassivate(HttpSessionEvent evt) {
		System.out.println("session被钝化了!");
	}
}

与上例一样,编写Servlet,提供两个方法:一个向session中添加Person对象,另一个从session中移除Person对象:

public class ListenerServlet extends BaseServlet {
	public String addPerson(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		Person p = new Person("zhangSan", 23, "male");
		request.getSession().setAttribute("person", p);
		return "/index.jsp";
	}
	
	public String removePerson(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.getSession().removeAttribute("person");
		return "/index.jsp";
	}
}

在index.jsp页面中给出访问addPerson()和removePerson()的方法:

  <body>
    <a href="<c:url value='/ListenerServlet?method=addPerson'/>">addPerson</a>
    <br/>
    <a href="<c:url value='/ListenerServlet?method=removePerson'/>">removePerson</a>
    <br/>
  </body>

  • 打开index.jsp页面,这时Tomcat会创建session,必须在1分钟之前点击addPerson链接,这能保证在session被钝化之前把Person对象添加到session中;
  • 等待一分钟,这时session会被钝化,也就会调用Person的sessionWillPassivate();
  • 刷新一下index.jsp页面,这会使session活化,会调用Person的sessionDidActivate()方法。


Java web----监听器

标签:java web   监听器   

原文地址:http://blog.csdn.net/bluzelee2011/article/details/42739331

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