WEB23_监听器

短命女 2022-02-28 07:06 212阅读 0赞

## 一、监听器Listener ##

### 1.1、什么是监听器 ###

监听器就是监听某个对象的的状态变化的组件。  
监听器的相关概念：  
事件源：被监听的对象 —– 三个域对象 request session servletContext  
监听器：监听事件源对象 事件源对象的状态的变化都会触发监听器 —- 6+2  
注册监听器：将监听器与事件源进行绑定  
响应行为：监听器监听到事件源的状态变化时 所涉及的功能代码 —- 程序员编写代码

### 1.2、监听器有哪些 ###

第一维度：按照被监听的对象划分：ServletRequest域、HttpSession域、ServletContext域  
第二维度：监听的内容分：监听域对象的创建与销毁的，监听域对象的属性变化的  
![在这里插入图片描述][20190325140928992.png]

### 1.3、监听三大域对象的创建与销毁的监听器 ###

#### （1）监听ServletContext域的创建与销毁的监听器ServletContextListener ####

##### 1）Servlet域的生命周期 #####

何时创建：服务器启动创建  
何时销毁：服务器关闭销毁

##### 2）监听器的编写步骤（重点）： #####

编写一个监听器类去实现监听器接口  
覆盖监听器的方法  
需要在web.xml中进行配置—注册

package com.itheima.create;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    public class MyServletContextListener implements ServletContextListener{
    
    	@Override
    	//监听context域对象的创建
    	public void contextInitialized(ServletContextEvent sce) {
    		//得到的就是被监听的对象--ServletContext
    		ServletContext servletContext = sce.getServletContext();
    		
    		System.out.println("context创建了...");
    	}
    
    	@Override
    	//监听context域对象的销毁
    	public void contextDestroyed(ServletContextEvent sce) {
    		System.out.println("context销毁了...");
    	}
    	
    }

需要在web.xml中进行配置—注册

<listener>
      	<listener-class>com.itheima.create.MyServletContextListener</listener-class>
      </listener>

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#### （2）ServletContextListener监听器的主要作用 ####

a、初始化的工作：初始化对象，初始化数据 —- 加载数据库驱动连接池的初始化  
b、加载一些初始化的配置文件 — spring的配置文件  
c、任务调度—-定时器—-Timer/TimerTask

//开启一个计息任务调度----每天晚上12点 计息一次
    		Timer timer = new Timer();
    		//task:任务  firstTime：第一次执行时间  period：间隔执行时间
    		//timer.scheduleAtFixedRate(task, firstTime, period);
    		timer.scheduleAtFixedRate(new TimerTask() {
    			
    			@Override
    			public void run() {
    				System.out.println("银行计息了....");
    			}
    		}, new Date(), 5000);

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//修改成银行真实计息业务
    		//1、起始时间： 定义成晚上12点
    		//2、间隔时间：24小时
    		SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
    		String currentTime = "2019-03-25 14:24:00";
    		Date parse = null;
    		try {
    			parse = format.parse(currentTime);
    		} catch (Exception e) {
    			System.out.println(e);
    		}
    		timer.scheduleAtFixedRate(new TimerTask() {
    			
    			@Override
    			public void run() {
    				System.out.println("银行计息了...");
    			}
    		}, parse, 24*60*1000);

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#### （3）监听Httpsession域的创建与销毁的监听器HttpSessionListener ####

HttpSession对象的生命周期：  
何时创建：第一次调用request.getSession时创建  
何时销毁：服务器关闭销毁、session过期 、手动销毁  
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#### （4）监听ServletRequest域创建与销毁的监听器ServletRequestListener ####

ServletRequest的生命周期：  
创建：每一次请求都会创建request  
销毁：请求结束  
ServletRequestListener的方法：

### 1.4、监听三大域对象的属性变化的 ###

#### (1) 域对象的通用的方法： ####

setAttribute(name,value)  
— 触发添加属性的监听器的方法  
attributeReplace(name）  
— 触发修改属性的监听器的方法  
getAttribute(name)  
removeAttribute(name)  
— 触发删除属性的监听器的方法

#### (2) ServletContextAttibuteListener监听器 ####

package com.itheima.attribute;
    
    import java.io.IOException;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class TestMySerrvletContextAttributeListener extends HttpServlet {
    
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		ServletContext servletContext = this.getServletContext();
    		
    		//想context域中存数据
    		servletContext.setAttribute("name", "tom");
    		
    		//改context数据
    		servletContext.setAttribute("name", "lucy");
    		
    		//删除context数据
    		servletContext.removeAttribute("name");
    	}
    
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

package com.itheima.attribute;
    
    import javax.servlet.ServletContextAttributeEvent;
    import javax.servlet.ServletContextAttributeListener;
    
    public class MyServletContextAttributeListener implements ServletContextAttributeListener{
    
    	@Override
    	public void attributeAdded(ServletContextAttributeEvent scab) {
    		//放到域中的属性
    		System.out.println(scab.getName());//放到域中的name
    		System.out.println(scab.getValue());//放到域中的value
    	}
    
    	@Override
    	public void attributeRemoved(ServletContextAttributeEvent scab) {
    		//删除域中的属性
    		System.out.println(scab.getName());//删除域中的name
    		System.out.println(scab.getValue());//删除域中的value
    	}
    
    	@Override
    	public void attributeReplaced(ServletContextAttributeEvent scab) {
    		System.out.println(scab.getName());//获得修改前的name
    		System.out.println(scab.getValue());//获得修改前的value
    	}
    
    }

![在这里插入图片描述][20190325145819988.png]  
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#### (3) HttpSessionAttributeListener监听器（同上） ####

\#\#\#\#(4) ServletRequestAriibuteListenr监听器（同上）

### 5．与session中的绑定的对象相关的监听器（对象感知监听器） ###

#### (1)即将要被绑定到session中的对象有几种状态 ####

绑定状态：就一个对象被放到session域中  
解绑状态：就是这个对象从session域中移除了  
钝化状态：是将session内存中的对象持久化（序列化）到磁盘  
活化状态：就是将磁盘上的对象再次恢复到session内存中

面试题：当用户很对时，怎样对服务器进行优化？

#### (2)绑定与解绑的监听器HttpSessionBindingListener ####

package com.itheima.domain;
    
    import javax.servlet.http.HttpSessionBindingEvent;
    import javax.servlet.http.HttpSessionBindingListener;
    //与session中的绑定的对象相关的监听器（对象感知监听器）
    public class Person implements HttpSessionBindingListener{
    	private String id;
    	private String name;
    	public String getId() {
    		return id;
    	}
    	public void setId(String id) {
    		this.id = id;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	@Override
    	//绑定的方法
    	public void valueBound(HttpSessionBindingEvent event) {
    		System.out.println("person被绑定了...");
    	}
    	@Override
    	//解绑方法
    	public void valueUnbound(HttpSessionBindingEvent event) {
    		System.out.println("person被解绑了...");
    	}
    }

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package com.itheima.domain;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    
    public class TestPersonBindingServlet extends HttpServlet {
    
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		HttpSession session = request.getSession();
    		
    		//将Person对象绑定到session中
    		Person p = new Person();
    		p.setId("100");
    		p.setName("zhangsanfeng");
    		
    		session.setAttribute("person", p);
    		
    		//将Person对象从session域中解绑
    		session.removeAttribute("person");		
    	}
    
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

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#### (3)钝化与活化的监听器HttpSessionActivationListener ####

可以通过配置文件 指定对象钝化时间 — 对象多长时间不用被钝化  
在META-INF下创建一个context.xml  
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##### context.xml文件内容： #####

<?xml version="1.0" encoding="UTF-8"?>
    <Context>
     
     
     <Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1">																				maxIdleSwap="1">
      <Store className="org.apache.catalina.session.FileStore" directory="itcast205" />
     </Manager>
    </Context>

com.itheima.domain.Customer

package com.itheima.domain;
    
    import java.io.Serializable;
    
    import javax.servlet.http.HttpSessionActivationListener;
    import javax.servlet.http.HttpSessionEvent;
    
    public class Customer implements HttpSessionActivationListener,Serializable{
    	private String id;
    	private String name;
    	public String getId() {
    		return id;
    	}
    	public void setId(String id) {
    		this.id = id;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	@Override
    	//钝化
    	public void sessionWillPassivate(HttpSessionEvent se) {
    		System.out.println("customer被钝化了...");
    	}
    	@Override
    	//活化
    	public void sessionDidActivate(HttpSessionEvent se) {
    		System.out.println("customer被活化了...");
    	}
    	
    }

package com.itheima.domain;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    public class TestCutomerActiveServlet extends HttpServlet {
    
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		
    		HttpSession session = request.getSession();
    		
    		//将customer放到session中
    		Customer customer = new Customer();
    		customer.setId("200");
    		customer.setName("lucy");
    		session.setAttribute("customer", customer);
    		System.out.println("customer被放到session域中了");
    		
    	}
    
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

package com.itheima.domain;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    public class TestCutomerActiveServlet2 extends HttpServlet {
    
    	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		//当向Session中存取登录信息时
    		HttpSession session = request.getSession();
    		Customer customer = (Customer) session.getAttribute("customer");
    		System.out.println(customer.getName());
    	}
    
    	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    }

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被钝化到work/catalina/localhost/的文件  
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## [二、邮箱服务器][Link 1] ##

### 1．邮箱服务器的基本概念 ###

邮件的客户端：可以只安装在电脑上的也可以是网页形式的  
邮件服务器：起到邮件的接受与推送的作用  
邮件发送的协议：  
协议：就是数据传输的约束  
接受邮件的协议：POP3 IMAP

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[Link 1]: https://blog.csdn.net/weixin_41835916/article/details/80849232