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 {@Overridepublic void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {System.out.println("增加值");}@Overridepublic void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {System.out.println("删除值");}@Overridepublic 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;@Overridepublic void sessionCreated(HttpSessionEvent httpSessionEvent) {System.out.println("seesion创建并调用监听");//通过事件获取sessionServletContext servletContext = httpSessionEvent.getSession().getServletContext();this.OnlineUserNumber++;servletContext.setAttribute("userNumber",this.OnlineUserNumber);}@Overridepublic void sessionDestroyed(HttpSessionEvent httpSessionEvent) {System.out.println("seesion销毁并调用监听");//通过事件获取sessionServletContext 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 {@Overrideprotected 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);}
}