自動監聽器 PropertiesListener

import javax.servlet.*;

/**
  * 自動監聽器
  *
  */
public class PropertiesListener implements ServletContextListener  {
     
     /**
      * 自動監聽時鐘
     */
     private PropertiesTimer rt = null;
     
     public void contextInitialized(ServletContextEvent event) {
         String status = "Properties listener start .";
         event.getServletContext().log(status);
         System.out.println(status);
         
         // 啟用自動監聽時鐘
        rt = new PropertiesTimer(15, event.getServletContext());
         rt.start();
     }
     
     public void contextDestroyed(ServletContextEvent event) {
         String status = "Properties listener stop .";
         event.getServletContext().log(status);
         System.out.println(status);
         
         // 停止自動監聽時鐘
        if (rt != null) {
             rt.stop();
         }
     }
 }
 

import java.util.*;
import javax.servlet.*;


/**
  * 自動監聽時鐘
  *
  */
public class PropertiesTimer {
     
     private final Timer timer = new Timer();
     private final int sec;
     private ServletContext context = null;
     
     public PropertiesTimer(int seconds, ServletContext context) {
         sec = seconds;
         this.context = context;
     }
     
     /**
      * 啟動自動監聽任務
     */
     public void start() {
         
         // 取得當前日期時間
        Date date = new Date();
         
         // 執行自動監聽計劃
        timer.schedule(new PropertiesTask(this.context), date, sec * 1000);
     }
     
     /**
      * 停止自動監聽任務
     */
     public void stop() {
         timer.cancel();

     }

 }
 

import java.io.IOException;
import java.io.*;
import java.util.*;

import javax.servlet.*;
/**
  * 自動監聽任務
 * @author stephen
  *
  */
public class PropertiesTask extends TimerTask {
     
     private ServletContext context = null;
     /**
      * 配置檔案的最後更新時間
     */
     private long lastModified = 0;
     
     /**
      * 構造一個自動更新任務
     * @param context
      */
     public PropertiesTask(ServletContext context){
         this.context = context;
         System.out.println("A task instance is created now."); // 任務在整個 application 週期內只建立一次。
    }
     
     /**
      * 每次執行任務時顯示一個隨機數。
     */
     public void todoTestRandom(){
         System.out.println("Task running");
         context.setAttribute("random", String.valueOf(Math.random()));
         System.out.println((String)context.getAttribute("random"));
     }
     
     /**
      * 監聽配置檔案是否被更新。
     */
     public void todoTestFileStatus(){
         System.out.println("Getting file status");
         System.out.println(this.isFileUpdated("WEB-INF/platforms/test.properties"));
     }
     
     /**
      * 監聽配置檔案是否被更新，自動更新檔案中的配置項儲存到 application 變數中。
     */
     public void todo(){
         String filename = "WEB-INF/platforms/test.properties";
         if(this.isFileUpdated(filename)){
             
             System.out.println("Getting properties");
             try{
                 this.loadProperties("test", filename);
             }catch(IOException ioe){
                 System.err.println(ioe.getMessage());
             }
         }
         System.out.println("Test value is: " + this.getTestProperty("name"));
     }
     
     public void run() {
         todoTestRandom();
         todo();
         //todo();
    }
     
     /**
      * 判斷物理檔案是否已被更新
     * @param filename 物理檔名
     * @return 是 true 否 false
      */
     private boolean isFileUpdated(String filename){
         File file = new File(context.getRealPath(filename));
         if(file.isFile()){
             long lastUpdateTime = file.lastModified();
             if(lastUpdateTime > this.lastModified){
                 System.out.println("The properties file was modified.");
                 this.lastModified = lastUpdateTime;
                 return true;
             }else{
                 System.out.println("The properties file was not modified.");
                 return false;
             }
         }else{
             System.out.println("The path does not point to a file.");
             return false;
         }
     }
     
     /**
      * 獲取配置檔案
     * @param key
      * @param filename
      * @return
      */
     public void loadProperties(String key, String filename) throws IOException{
         Properties prop = new Properties();
         InputStream stream = context.getResourceAsStream(filename);
         prop.load(stream);
         if(stream!=null){
             stream.close();
         }
         context.setAttribute(key, prop);
     }
     
     /**
      * 從 application 取配置項的值
     * @param key 配置項的鍵名
     * @return 配置項的值
     */
     public String getTestProperty(String key){
         Properties prop = (Properties)context.getAttribute("test");
         if(prop==null){
             return null;
         }else{
             return (String)prop.get(key);
         }
     }

 }
 

<?xml version="1.0" encoding="GB18030"?>
<web-app version="2.4" 
     xmlns="http://java.sun.com/xml/ns/j2ee" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
     http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
      
<listener>
     <listener-class>org.stephencat.listener.PropertiesListener</listener-class>
</listener>    
</web-app>