java web-- listen

1. HttpSessionActivationListener

1). 监听实现了该接口和 Serializable 接口的 Java 类的对象随 session 钝化和活化事件

> 活化: 从磁盘中读取 session 对象
> 钝化: 向磁盘中写入 session 对象
> session 对象存储在tomcat 服务器的 workCatalinalocalhostcontextPath 目录下. SESSION.SER
2). 该监听器不需要在 web.xml 文件中进行配置.

3).

/ /在活化之后被调用.
public void sessionDidActivate(HttpSessionEvent se)

/ /在钝化之前被调用
public void sessionWillPassivate(HttpSessionEvent se)

HttpSessionEvent: getSession()

4). 该监听器较少被使用.

2. HttpSessionBindingListener

1). 监听实现了该接口的 Java 类的对象被绑定到 session 或从 session 中解除绑定的事件.

//当前对象被绑定到 session 时调用该方法
public void valueBound(HttpSessionBindingEvent event)

//当前对象从 session 中解除绑定调用该方法
public void valueUnbound(HttpSessionBindingEvent event)

2). 注意: 该监听器不需要在 web.xml 文件中进行配置.

3). HttpSessionBindingEvent:

getName()
getValue()
getSession()

4). 该监听器较少被使用.

3. XxxAttributeListener

1). 监听 ServletContext, HttpSession, ServletRequest 中添加属性, 替换属性, 移除属性的事件监听器.

2). 以 ServletRequestAttributeListener 为例:

//添加属性时被调用
public void attributeAdded(ServletRequestAttributeEvent srae) {
System.out.println("向 request 中添加了一个属性...");
}

//移除属性时被调用
@Override
public void attributeRemoved(ServletRequestAttributeEvent srae) {
System.out.println("从 request 中移除了一个属性...");
}

//替换属性时被调用.
@Override
public void attributeReplaced(ServletRequestAttributeEvent srae) {
System.out.println("request 中属性替换了...");
}

3). 这三个 ServletContextAttributeListener,
ServletRequestAttributeListener, HttpSessionAttributeListener 监听器较少被使用.

4). API:

ServletRequestAttributeEvent:
> getName(): 获取属性的名字
> getValue(): 获取属性的值.

4. ServletRequestListener & HttpSessionListener

1). 和 ServletContextListener 类似。

2). 利用 ServletRequestListener、HttpSessionListener 以及 ServletContextListener 可以把 request, session
及 application 的生命周期进一步的做一了解.

> request: 是一个请求, 当一个响应返回时, 即被销毁. 当发送一个请求时被创建. 注意, 请求转发的过程是一个 request 对象.
重定向是两个请求
> session: 当第一次访问 WEB 应用的一个 JSP 或 Servlet 时, 且该 JSP 或 Servlet 中还需要创建 session 对象. 此时服务器会
创建一个 session 对象.
session 销毁: session 过期, 直接调用 session 的 invalidate 方法, 当前 web 应用被卸载(session 可以被持久化).
* 关闭浏览器, 并不意味着 session 被销毁, 还可以通过 sessionid 找到服务器中的 session 对象.

JSESSIONID=F4119DE0FC93ED38E8EC83B24CFA3B81
http://localhost:8989/day_40/session.jsp;jsessionid=F4119DE0FC93ED38E8EC83B24CFA3B81
> application: 贯穿于当前的 WEB 应用的生命周期. 当前 WEB 应用被加载时创建 application 对象, 当前 WEB 应用被卸载时
销毁 application 对象.

5. ServletContextListener:

1). what: 监听 ServletContext 对象被创建或销毁的 Servlet 监听器

2). how:

> 创建一个实现了 ServletContextListener 的类, 并且实现其中的两个方法
public class HelloServletContextListner implements ServletContextListener
> 在 web.xml 文件中配置 Listener
<listener>
<listener-class>com.atguigu.javaweb.test.HelloServletContextListner</listener-class>
</listener>
3). why: ServletContextListener 是最常用的 Listener, 可以在当前 WEB 应用被加载时对当前 WEB 应用的相关资源进行初始化操作:
创建数据库连接池, 创建 Spring 的 IOC 容器, 读取当前 WEB 应用的初始化参数 ...

4). API:

/ / SerlvetContext 对象被创建(即, 当前 WEB 应用被加载时)的时候, Servlet 容器调用该方法.
public void contextInitialized(ServletContextEvent sce)

// SerlvetContext 对象被销毁之前(即, 当前 WEB 应用被卸载时)的时候, Servlet 容器调用该方法.
public void contextDestroyed(ServletContextEvent sce)
ServletContextEvent 中的: getServletContext() 获取 ServletContext

6.代码区

package com.atguigu.javaweb.test;

import java.io.Serializable;

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

public class Customer implements Serializable,HttpSessionBindingListener, HttpSessionActivationListener{

    private String time;
    
    public void setTime(String time) {
        this.time = time;
    }
    
    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        System.out.println("绑定到 session");
        Object value = event.getValue();
        System.out.println(value == this);
        System.out.println(event.getName()); 
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println("从 sessoin 中解除绑定");
    }

    @Override
    public void sessionWillPassivate(HttpSessionEvent se) {
        System.out.println("从内存中写到磁盘上...");
    }

    @Override
    public void sessionDidActivate(HttpSessionEvent se) {
        System.out.println("从磁盘中读取出来...");
    }
    
    @Override
    public String toString() {
        return super.toString() + ", time: " + time;
    }

}

Customer

package com.atguigu.javaweb.test;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
    
public class HelloServletContextListner 
    implements ServletContextListener, ServletRequestListener, HttpSessionListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("ServletContext 对象被创建。 " + sce.getServletContext());
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("ServletContext 对象被销毁。" + sce.getServletContext());
    }

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("HttpSession 被创建。");
    }
       
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        // TODO Auto-generated method stub
        System.out.println("HttpSession 被销毁");
    }

    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        // TODO Auto-generated method stub
        System.out.println("ServletRequest 被销毁");
    }

    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        // TODO Auto-generated method stub
        System.out.println("ServletRequest 被创建");
    }

}

HelloServletContextListner

package com.atguigu.javaweb.test;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class TestAttributeListener implements ServletContextAttributeListener,
    ServletRequestAttributeListener, HttpSessionAttributeListener{

    @Override
    public void attributeAdded(ServletRequestAttributeEvent srae) {
        System.out.println("向 request 中添加了一个属性: " + srae.getName() + ": " + srae.getValue());
    }

    @Override
    public void attributeRemoved(ServletRequestAttributeEvent srae) {
        System.out.println("从 request 中移除了一个属性: " + srae.getName() + ": " + srae.getValue());
    }

    @Override
    public void attributeReplaced(ServletRequestAttributeEvent srae) {
        System.out.println("request 中属性替换了: " + srae.getName() + ": " + srae.getValue());
    }

    @Override
    public void attributeAdded(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void attributeRemoved(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void attributeAdded(HttpSessionBindingEvent se) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent se) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent se) {
        // TODO Auto-generated method stub
        
    }

}
/*ServletRequest 被创建
request 中属性替换了: org.apache.catalina.ASYNC_SUPPORTED: true
向 request 中添加了一个属性: name: ABCD
-----------------------------
request 中属性替换了: name: ABCD
-----------------------------
从 request 中移除了一个属性: name: DEFG
-----------------------------
ServletRequest 被销毁
*/

TestAttributeListener

package com.atguigu.javaweb.test;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestServlet
 */
public class TestServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("requestKey", "requestValue2");
        request.getRequestDispatcher("/test.jsp").forward(request, response);
    //    response.sendRedirect("test.jsp");
    }

}

TestServlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
 
 
  <listener>
      <listener-class>com.atguigu.javaweb.test.TestAttributeListener</listener-class>
  </listener>
  <listener>
    <listener-class>com.atguigu.javaweb.test.HelloServletContextListner</listener-class>
  </listener>
  
  
  <servlet>
    <description></description>
    <display-name>TestServlet</display-name>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>com.atguigu.javaweb.test.TestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/TestServlet</url-pattern>
  </servlet-mapping>
</web-app>

web.xml

<%@page import="java.util.Date"%>
<%@page import="com.atguigu.javaweb.test.Customer"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>HttpSessionBindingListener</h4>
    
    <%--
        Customer customer = new Customer();
        session.setAttribute("customer", customer);
    
        System.out.println("------------------------");
        
        session.removeAttribute("customer");
    --%>
    
    <%
        Customer customer = (Customer)session.getAttribute("customer");
    
        if(customer == null){
            customer = new Customer();
            customer.setTime("" + new Date()); 
            session.setAttribute("customer", customer);
            System.out.println("创建一个新的 Customer 对象: " + customer + ", 并放入到 session 中");
        }else{
            System.out.println("从 session 中读取到 Customer 对象: " + customer);
            
        }
    %>
<!-- ServletRequest 被创建
request 中属性替换了: org.apache.catalina.ASYNC_SUPPORTED: true
绑定到 session
true
customer
创建一个新的 Customer 对象: com.atguigu.javaweb.test.Customer@2f089b0d, time: Wed Jan 17 15:03:43 CST 2018, 并放入到 session 中
ServletRequest 被销毁
 -->    
</body>
</html>

HttpSessionBindingListener.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>Index Page</h4>
    
    <a href="test.jsp">To Test Page</a>
    
    <%-- 
        request.setAttribute("requestKey", "requestValue");
        <jsp:forward page="/test.jsp"></jsp:forward>
    --%>
    
    <br><br>
    
    <a href="TestServlet">TestServlet</a>
<!-- ServletRequest 被创建
request 中属性替换了: org.apache.catalina.ASYNC_SUPPORTED: true
HttpSession 被创建。
ServletRequest 被销毁 -->    
    
</body>
</html>

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" session="false"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>

    <h4>Session Page</h4>
    
    <% 
        HttpSession session = request.getSession(true);
        //session.setMaxInactiveInterval(10);
        session.invalidate();
    %>
<!-- ServletRequest 被创建
request 中属性替换了: org.apache.catalina.ASYNC_SUPPORTED: true
HttpSession 被创建。
HttpSession 被销毁
ServletRequest 被销毁 -->
</body>
</html>

session.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <% 
        request.setAttribute("name", "ABCD");
        System.out.println("-----------------------------");
        
        request.setAttribute("name", "DEFG");
        System.out.println("-----------------------------");
        
        request.removeAttribute("name");
        System.out.println("-----------------------------");
    %>
<!-- ServletRequest 被创建
request 中属性替换了: org.apache.catalina.ASYNC_SUPPORTED: true
HttpSession 被创建。
向 request 中添加了一个属性: name: ABCD
-----------------------------
request 中属性替换了: name: ABCD
-----------------------------
从 request 中移除了一个属性: name: DEFG
-----------------------------
ServletRequest 被销毁
 -->    
</body>
</html>

test-attribute-listener.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
    
    <h4>Test Page</h4>
    
    <%= request.getAttribute("requestKey") %>
    
</body>
</html>

test.jsp