Java學習路線-50：Servlet監聽器Listener

課時12 什麼叫監聽器Listener

AWT、SAX

監聽器：

一個接口，内容由使用者實作

需要注冊

監聽器中的方法，會在特殊事件發生時被調用

觀察者

事件源

事件

監聽器

課時13 監聽器概述以及生命周期監聽器

1、ServletContext
    生命周期監聽 ServletContextListener
        建立 contextInitialized
        銷毀 contextDestroyed
        ServletContextEvent
            -getServletContext()

    屬性監聽 ServletContextAttributeListener
        添加 attributeAdded
        替換 attributeReplaced
        移除 attributeRemoved
        ServletContextAttributeEvent
            -getName()
            -getValue()


2、HttpSession
    生命周期監聽 HttpSessionListener
        建立 sessionCreated
        銷毀 sessionDestroyed
        HttpSessionEvent
            -getSession()

    屬性監聽 HttpSessionAttributeListener
        添加 attributeAdded
        替換 attributeReplaced
        移除 attributeRemoved
        HttpSessionBindingEvent
            -getSession()
            -getName()
            -getValue()


3、ServletRequest
    生命周期監聽 ServletRequestListener
        建立 requestDestroyed
        銷毀 requestInitialized
        ServletRequestEvent
            -getServletRequest()
            -getServletContext()

    屬性監聽 ServletRequestAttributeListener
        添加 attributeAdded
        替換 attributeReplaced
        移除 attributeRemoved
        ServletRequestAttributeEvent
            -getName()
            -getValue()
      

編寫監聽器

繼承父類，實作方法

package com.pengshiyu.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class AListener implements ServletContextListener{

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {

    }
}
      

配置監聽器web.xml

<listener>
    <listener-class>com.pengshiyu.listener.AListener</listener-class>
</listener>      

課時14 監聽器之屬性監聽器

設定屬性

package com.pengshiyu.servlet;

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

public class AServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        getServletContext().setAttribute("key", "value");
        response.getWriter().print("Hello");
    }
}
      

監聽屬性變化

package com.pengshiyu.listener;

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

public class AListener implements ServletContextAttributeListener {

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

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

    @Override
    public void attributeReplaced(ServletContextAttributeEvent event) {
        System.out.println(event.getName() + ":" + event.getValue() + "->" +
                event.getServletContext().getAttribute(event.getName()));
    }
}
      

課時15 感覺監聽器

都與HttpSession相關

添加到JavaBean上

不需要再web.xml中注冊

package com.pengshiyu.bean;

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

public class User implements HttpSessionBindingListener {
    private String name;

    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        System.out.println("session值綁定了: " + event.getName() + "=" + event.getValue());
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println("session值解除綁定了: " + event.getName() + "=" + event.getValue());
    }
}      

package com.pengshiyu.servlet;

import com.pengshiyu.bean.User;

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

public class AServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        User user = new User();
        request.getSession().setAttribute("user", user);

        response.getWriter().print("Hello");
    }
}
      

課時16 session的序列化

session會在程式關閉的時候序列化到硬碟

再次啟動程式，硬碟上的session會反序列化到記憶體

課時17 session的鈍化和活化

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

鈍化儲存，活化重新加載

課時18 監聽器之HttpSessionActivationListener

package com.pengshiyu.bean;

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

public class User implements HttpSessionActivationListener, java.io.Serializable {
    @Override
    public void sessionWillPassivate(HttpSessionEvent se) {
        
    }

    @Override
    public void sessionDidActivate(HttpSessionEvent se) {

    }
}