监听器

一、监听器

https://www.cnblogs.com/zhai1997/p/11651085.html摘抄

监听器即监视域对象的创建与销毁以及域对象的属性的变化。

监听ServletContext域对象的创建与销毁：实现ServletContextListener 接口

监听HttpSession域对象的创建与销毁：实现HttpSessionListener 接口（在Session被创建的时候监听器被创建）

监听ServletRequest域对象的创建与销毁：实现ServletRequesttListener 接口

监听ServletContext域对象属性：实现ServletContextAttributeListener 接口

监听HttpSession域对象属性：实现HttpSessionAttributeListener 接口

监听ServletRequest域对象属性：实现ServletRequestAttributetListener 接口

两种方式：

     1）直接new listener

     2）在web.xml中配置

   
        net.pp.FirstServletContextListener
    

FirstServletContextListener.java

package net.pp;

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

public class FirstServletContextListener implements ServletContextListener{

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("Servletcontext初始化了");

    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("Servletcontext销毁了");
    }
}

FirstHttpSessionListener.java

package net.pp;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import javax.servlet.http.HttpSessionBindingEvent;

@WebListener()
public class FirstHttpSessionListener implements HttpSessionListener{

    // Public constructor is required by servlet spec
    public FirstHttpSessionListener() {
    }

    public void sessionCreated(HttpSessionEvent se) {
        System.out.println(se.getSession().getId());
    }

    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("session销毁了！");
    }


}

 

2、监听三大域对象的属性变化

二、对象感知监听器

与session中绑定的对象相关。

User.java

package net.pp.bean;

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

public class User implements HttpSessionBindingListener{
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public void valueBound(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("对象被绑定了！");
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("对象被解除绑定了！");
    }
}

TestBindingServlet.java

package net.pp.servlet;

import net.pp.bean.User;

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

@WebServlet(name = "TestBindingServlet", urlPatterns = "/testBind")
public class TestBindingServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

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

        HttpSession session =  request.getSession();
        User user = new User();
        user.setId(1);
        user.setName("wen");
        //绑定对象
        session.setAttribute("user",user);
        //解除绑定
        session.removeAttribute("user");

    }
}