监听器

监听器介绍

　　监听器 - Listener

　　监听器（Listener）是J2EE Servlet模块下的组件

　　Listener的作用对web应用对象的行为进行监控

　　通过Listener监听自动触发指定的功能代码

　　

 　　

第一个监听器

　　

package com.imooc.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
@WebListener
public class FirstListener implements ServletContextListener {

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("监听器销毁");
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        System.out.println("监听器初始化");
    }

}

<listener>
　　<listener-class>com.imooc.listener.FirstListener</listener-class>
</listener>

内置对象监听器

　　

 

 案例应用

　　请求流量分析统计

　　　　

package com.imooc.total;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;

public class RequestTotal implements ServletContextListener,ServletRequestListener {

    @Override
    public void requestDestroyed(ServletRequestEvent arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void requestInitialized(ServletRequestEvent arg0) {
        /**
         * 监听请求，每次请求来临时，记录时间段的请求次数
         * 
         */
        
        //获取ServletContext对象
        ServletContext context = arg0.getServletContext();
        
        //取出属性对象
        List<String> timeArray = (List<String>) context.getAttribute("timeArray");
        List<Integer> valueArray = (List<Integer>) context.getAttribute("valueArray");
        //定义一个时间类型的对象
        Date date = new Date();
        
        //时间格式化
        SimpleDateFormat hourMinute = new SimpleDateFormat("HH:mm");
        //对小时和分钟格式化
        String time = hourMinute.format(date);
        
        //判断当前时间在不在集合里
        if(timeArray.indexOf(time) == -1) {
            //时间集合里增加这个时间段
            timeArray.add(time);
            //在请求记录集合里，初始化有一次请求
            valueArray.add(1);
            
            //保存ServletContext对象里
            context.setAttribute("timeArray", timeArray);
            context.setAttribute("valueArray", valueArray);
        }else {
            //获取该时间段索引
            int index = timeArray.indexOf(time);
            //根据索引获取值
            int value = valueArray.get(index);
            //根据索引累加值
            valueArray.set(index, value+1);
            
            //保存属性
            
            context.setAttribute("valueArray", valueArray);
            
        }
        
        
        
    }

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        // 初始化时间集合，累加请求集合
        
        List timeArray = new ArrayList();
        List valueArray = new ArrayList();
        
        //获取ServletContext对象
        ServletContext context = arg0.getServletContext();
        
        //把timeArray当属性保存在ServletContext里
        context.setAttribute("timeArray", timeArray);
        
        context.setAttribute("valueArray", valueArray);
        
    }

}

xml配置

　　

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>request-total</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <listener>
      <listener-class>com.imooc.total.RequestTotal</listener-class>
  </listener>
</web-app>

入门百度Echarts组件

　　

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
    <script type="text/javascript" src="js/echarts.min.js"></script>
    <script type="text/javascript" src="js/jquery-3.5.1.min.js"></script>
</head>
<body>
    <!-- 为ECharts准备一个具备大小（宽高）的Dom -->
    <div id="main" style=" 600px;height:400px;"></div>
    <script type="text/javascript">
    
        function showCase(){
            //ajax的使用
               $.ajax(
                   {
                   url:"./rt",
                   type:"get",
                   dataType:"json",
                   success : function(json) {
                       // data = jQuery.parseJSON(data);  //dataType指明了返回数据为json类型，故不需要再反序列化
                       console.log(json);
                       console.log(json.timeArray);
                       console.log(json.vauleArray);
                       // 基于准备好的dom，初始化echarts实例
                       var myChart = echarts.init(document.getElementById('main'));

                       // 指定图表的配置项和数据
                       var option = {
                           title: {
                               text: '请求流量数据表'
                           },
                           tooltip: {},
                           legend: {
                               data:['访问量']
                           },
                           xAxis: {
                               data: json.timeArray
                           },
                           yAxis: {},
                           series: [{
                               name: '次数',
                               type: 'bar',
                               data: json.valueArray
                           }]
                       };

                       // 使用刚指定的配置项和数据显示图表。
                       myChart.setOption(option);
                   },
                   error:function(){
                       alert("请求失败");
                   }

                   }
               )

        }
           window.setInterval("showCase()",1000);
    </script>
    
</body>
    

</html>

package com.imooc.total;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;

public class RequestTotal implements ServletContextListener,ServletRequestListener {

    @Override
    public void requestDestroyed(ServletRequestEvent arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void requestInitialized(ServletRequestEvent arg0) {
        /**
         * 监听请求，每次请求来临时，记录时间段的请求次数
         * 
         */
        //获取HttpServletRequest对象
        HttpServletRequest request = (HttpServletRequest)arg0.getServletRequest();
        
        //获取请求的URL
        String url = request.getRequestURL().toString();
        
        if(url.endsWith("/rt") == true) {
            return;
        }
        
        //获取ServletContext对象
        ServletContext context = arg0.getServletContext();
        
        //取出属性对象
        List<String> timeArray = (List<String>) context.getAttribute("timeArray");
        List<Integer> valueArray = (List<Integer>) context.getAttribute("valueArray");
        //定义一个时间类型的对象
        Date date = new Date();
        
        //时间格式化
        SimpleDateFormat hourMinute = new SimpleDateFormat("HH:mm");
        //对小时和分钟格式化
        String time = hourMinute.format(date);
        
        //判断当前时间在不在集合里
        if(timeArray.indexOf(time) == -1) {
            //时间集合里增加这个时间段
            timeArray.add(time);
            //在请求记录集合里，初始化有一次请求
            valueArray.add(1);
            
            //保存ServletContext对象里
            context.setAttribute("timeArray", timeArray);
            context.setAttribute("valueArray", valueArray);
        }else {
            //获取该时间段索引
            int index = timeArray.indexOf(time);
            //根据索引获取值
            int value = valueArray.get(index);
            //根据索引累加值
            valueArray.set(index, value+1);
            
            //保存属性
            
            context.setAttribute("valueArray", valueArray);
            
        }
        
        
        
    }

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {
        // 初始化时间集合，累加请求集合
        
        List timeArray = new ArrayList();
        List valueArray = new ArrayList();
        
        //获取ServletContext对象
        ServletContext context = arg0.getServletContext();
        
        //把timeArray当属性保存在ServletContext里
        context.setAttribute("timeArray", timeArray);
        
        context.setAttribute("valueArray", valueArray);
        
    }

}

package com.imooc.total;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.ServletContext;
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 com.alibaba.fastjson.JSON;

/**
 * Servlet implementation class RequestTotalServlet
 */
@WebServlet("/rt")
public class RequestTotalServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public RequestTotalServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        
//        out.println("<h1>流量统计计算器</h1>");
        
        ServletContext context = request.getServletContext();
        List<String> timeArray = (List) context.getAttribute("timeArray");
        List<Integer> valueArray = (List<Integer>) context.getAttribute("valueArray");
        
        
//        out.println(timeArray.toString()+"
");
//        out.println(valueArray.toString());
        
        //整合集合，采取map映射表的方式
        Map dict = new HashMap();
        //初始化键值对
        dict.put("timeArray", timeArray);
        dict.put("valueArray", valueArray);
        //转化为JSON字符串
        String json = JSON.toJSONString(dict);
        
        out.println(json);
        
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}