JSP之监听器Listener(二)

ServletContextAttributeListener

用于监听ServletContext也就是application范围内属性的变化，实现该结构主要重写三个方法

•  attributeAdded()方法：当向application中添加参数的时候会自动调用
• attributeRemoved()方法：当把application中的参数移除的时候调用
• attributeReplaced()方法：当修改application中的参数时调用

package com.huayu.listener;

import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.annotation.WebListener;
@WebListener
public class Listener3 implements ServletContextAttributeListener{
    
    @Override
    public void attributeAdded(ServletContextAttributeEvent event) {
        String named=event.getName().toString();
        String value=event.getValue().toString();
        System.out.println("application中添加了一个"+named+"变量值为"+value);
        
    }

    @Override
    public void attributeRemoved(ServletContextAttributeEvent event) {
        String named=event.getName().toString();
        String value=event.getValue().toString();
        System.out.println("application中添移除一个"+named+"变量值为"+value);
        
        
        
    }

    @Override
    public void attributeReplaced(ServletContextAttributeEvent event) {
        String named=event.getName().toString();
        String value=event.getValue().toString();
        System.out.println("application中"+named+"变量值变为"+value);
    }

}

ServletRequestListener

用来监听用户的请求到达，请求的结束

requestInitialized:用户请求到达，被初始化时触发该方法

requestDestroyed:用户请求结束，被销毁时触发该方法

ServletRequestAttributeListener

用来监听request范围内变量的变化

attributeAdded（）

attributeReplaced（）

attributeRemoved（）

package com.huayu.listener;

import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServletRequest;
@WebListener
public class Listener4 implements ServletRequestListener,ServletRequestAttributeListener{

    @Override
    public void requestDestroyed(ServletRequestEvent arg0) {

        HttpServletRequest request=(HttpServletRequest) arg0.getServletRequest();
        System.out.println("---发向"+request.getRequestURI()+"请求被销毁-----");
        
    }

    @Override
    public void requestInitialized(ServletRequestEvent arg0) {
        HttpServletRequest request=(HttpServletRequest) arg0.getServletRequest();
        System.out.println("---发向"+request.getRequestURI()+"请求被初始化-----");
    }

    @Override
    public void attributeAdded(ServletRequestAttributeEvent arg0) {
            ServletRequest request=arg0.getServletRequest();
            String name=arg0.getName();
            String value=arg0.getValue().toString();
            System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性");
        
    }

    @Override
    public void attributeRemoved(ServletRequestAttributeEvent arg0) {
        ServletRequest request=arg0.getServletRequest();
        String name=arg0.getName();
        String value=arg0.getValue().toString();
        System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性被删除");
        
    }

    @Override
    public void attributeReplaced(ServletRequestAttributeEvent arg0) {
        ServletRequest request=arg0.getServletRequest();
        String name=arg0.getName();
        String value=arg0.getValue().toString();
        System.out.println(request+"范围内添加了名为"+name+"值为"+value+"的属性被替换了");
        
    }

}

HttpSessionListener

用于监听用户session的创建和销毁

sessionCreated(HttpSessionEvent se)：当session

被建立的时候调用

 sessionDestroyed(HttpSessionEvent se)

当session没有任何客户端与之链接的时候执行

HttpSessionAttributeListener

使用方法同上