如何正确的使用servlet监听器

package com.learn;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import java.io.*;public class MyServletContextListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) {  System.out.println("Webapp initital.......");  ServletContext servletContext = sce.getServletContext();  InputStreamReader inputStreamReader = new InputStreamReader(servletContext.getResourceAsStream("/count/count.txt"));  BufferedReader bufferedReader = new BufferedReader(inputStreamReader);  try {   int icount = Integer.parseInt(bufferedReader.readLine());   icount++;   servletContext.setAttribute("count",icount);   System.out.println("Webapp initital success");  } catch (IOException e) {   e.printStackTrace();  } } @Override public void contextDestroyed(ServletContextEvent sce) {  System.out.println("webApp destroyed ........");  ServletContext servletContext = sce.getServletContext();  Integer count = (Integer) servletContext.getAttribute("count");  if(count != null){   count ++;   String filePath = servletContext.getRealPath("/count");   filePath = filePath+"/count.txt";   try {    PrintWriter printWriter = new PrintWriter(filePath);    printWriter.write(count);    printWriter.close();    System.out.println("webApp desdroyed success ");   } catch (FileNotFoundException e) {    e.printStackTrace();   }  } }}