06 监听器

SessionAttListenerDemo.java

package com.aistart.listener;

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



/*
* 使用步骤
* 1. 实现对应的Listener
* 2. 重写接口函数,监听对应的功能
* 3. 配置  @WebListener
 *
* */
@WebListener
public class SessionAttListenerDemo implements HttpSessionAttributeListener {

    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println("增加值");
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {

        System.out.println("删除值");
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

        System.out.println("修改值");
    }
}

SessionListenerDemo.java

package com.aistart.listener;

import javax.servlet.ServletContext;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;



/*
* 使用步骤
* 1. 实现对应的Listener
* 2. 重写接口函数,监听对应的功能
* 3. 配置  @WebListener
 *
* */
@WebListener
public class SessionListenerDemo implements HttpSessionListener {

    private int OnlineUserNumber = 0;
    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

        System.out.println("seesion创建并调用监听");

        //通过事件获取session
        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();

        this.OnlineUserNumber++;

        servletContext.setAttribute("userNumber",this.OnlineUserNumber);

    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

        System.out.println("seesion销毁并调用监听");

        //通过事件获取session
        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();

        this.OnlineUserNumber--;

        servletContext.setAttribute("userNumber",this.OnlineUserNumber);
    }
}

ProductController.java

package com.aistart.controller;

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({"/product/init","/product/add","/product/del"})
public class ProductController extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //1.先看有没有登录状态

        /*这个部分我们就可以放在过滤器中操作*/

        System.out.println("我开始操作了");

        Object userNumber = req.getServletContext().getAttribute("userNumber");

        System.out.println("当前在线人数"+userNumber);


    }
}