监听三大域对象的属性变化

(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   

 --- 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.itcast.attribute;

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

public class MyServletContextAttributeListener implements ServletContextAttributeListener{

	@Override
	public void attributeAdded(ServletContextAttributeEvent arg0) {
		System.out.println(arg0.getName());//添加域中的name
		System.out.println(arg0.getValue());//添加域中的value
	}

	@Override
	public void attributeRemoved(ServletContextAttributeEvent arg0) {
		// TODO Auto-generated method stub
		System.out.println(arg0.getName());//删除域中的name
		System.out.println(arg0.getValue());//删除域中的value
	}

	@Override
	public void attributeReplaced(ServletContextAttributeEvent arg0) {
		System.out.println(arg0.getName());//获得修改前的name
		System.out.println(arg0.getValue());//获得修改前的value
	}

}

package com.itcast.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 TestServletContextAttributeListener extends HttpServlet {
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	
		ServletContext servletContext = this.getServletContext();
		//添加
		servletContext.setAttribute("name", "tom");
		//修改
		servletContext.setAttribute("name", "lucy");
		//删除
		servletContext.removeAttribute("name");
	}


	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}


}

(3) HttpSessionAttributeListener监听器（同上）

(4) ServletRequestAriibuteListenr监听器（同上）