监听器的两个应用

一、获得当前在线人数

package com.bjsxt.listener;

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

/**
 * @program: JavaEE
 * @description
 * @author: wuhao
 * @create: 2019-12-13 09:41
 **/
public class OnlineListener implements HttpSessionListener, HttpSessionAttributeListener {
    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
        if ("employee".equals(httpSessionBindingEvent.getName())){
            //获得全局对象
            ServletContext servletContext = httpSessionBindingEvent.getSession().getServletContext();
            //获得在线人数
            Integer online = (Integer) servletContext.getAttribute("online");

            if (online == null) {
                online = 1;
            } else {
                online++;
            }
            //设置全局属性
            servletContext.setAttribute("online",online );
        }
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {

    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {

    }

    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        //注销session时 人数-1
        //获得全局对象
        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();

         Integer online = (Integer) servletContext.getAttribute("online");

         if (online==null){
             online=0;
         }else {
             online--;
         }

         servletContext.setAttribute("online",online );



    }
}

　　web.xml配置

<listener>
    <listener-class>com.bjsxt.listener.OnlineListener</listener-class>
</listener>

　二、监听用户的操作（日志文件）

package com.bjsxt.listener;

import javax.servlet.ServletRequest;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

/**
 * @program: JavaEE
 * @description
 * 日志
 * @author: wuhao
 * @create: 2019-12-12 19:28
 **/
public class UserListener implements ServletRequestListener {
    @Override
    public void requestDestroyed(ServletRequestEvent servletRequestEvent) {

    }

    @Override
    //监听发出的请求
    public void requestInitialized(ServletRequestEvent servletRequestEvent) {
        ServletRequest servletRequest = servletRequestEvent.getServletRequest();

        HttpServletRequest request =(HttpServletRequest)servletRequest;

        //获得远程请求的ip
        String  ip = request.getRemoteAddr();
        //获得请求的时间
        String date = new Date().toLocaleString();
        //获得请求的动作
        String requestURI = request.getRequestURI();
        String queryString = request.getQueryString();

        //把这写到日志文件中去
        try {
            PrintWriter printWriter = new PrintWriter(new FileWriter("D:/sxtOA.txt", true));

            printWriter.println("用户，ip为："+ip+"在"+date+"访问了程序的"+requestURI+"?"+queryString);

            printWriter.close();
        } catch (IOException e) {
            e.printStackTrace();

        }


    }
}

　　web.xml配置

<listener>
        <listener-class>com.bjsxt.listener.UserListener</listener-class>
    </listener>