Java 多线程 监听文件改动，文件一有改动就重新加载配置文件信息

自动监听器 PropertiesListener

package org.stephencat.listener;

import javax.servlet.*;

/**
 * 自动监听器
 * @author stephen
 *
 */
public class PropertiesListener implements ServletContextListener  {
    
    /**
     * 自动监听时钟
     */
    private PropertiesTimer rt = null;
    
    public void contextInitialized(ServletContextEvent event) {
        String status = "Properties listener start .";
        event.getServletContext().log(status);
        System.out.println(status);
        
        // 激活自动监听时钟
        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);
        
        // 停止自动监听时钟
        if (rt != null) {
            rt.stop();
        }
    }
}

自动监听时钟 PropertiesTimer

package org.stephencat.listener;
import java.util.*;
import javax.servlet.*;


/**
 * 自动监听时钟
 * @author stephen
 *
 */
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;
    }
    
    /**
     * 启动自动监听任务
     */
    public void start() {
        
        // 取得当前日期时间
        Date date = new Date();
        
        // 执行自动监听计划
        timer.schedule(new PropertiesTask(this.context), date, sec * 1000);
    }
    
    /**
     * 停止自动监听任务
     */
    public void stop() {
        timer.cancel();

    }

}

自动监听任务 PropertiesTask

package org.stephencat.listener;
import java.io.IOException;
import java.io.*;
import java.util.*;

import javax.servlet.*;
/**
 * 自动监听任务
 * @author stephen
 *
 */
public class PropertiesTask extends TimerTask {
    
    private ServletContext context = null;
    /**
     * 配置文件的最后更新时间
     */
    private long lastModified = 0;
    
    /**
     * 构造一个自动更新任务
     * @param context
     */
    public PropertiesTask(ServletContext context){
        this.context = context;
        System.out.println("A task instance is created now."); // 任务在整个 application 周期内只创建一次。
    }
    
    /**
     * 每次执行任务时显示一个随机数。
     */
    public void todoTestRandom(){
        System.out.println("Task running");
        context.setAttribute("random", String.valueOf(Math.random()));
        System.out.println((String)context.getAttribute("random"));
    }
    
    /**
     * 监听配置文件是否被更新。
     */
    public void todoTestFileStatus(){
        System.out.println("Getting file status");
        System.out.println(this.isFileUpdated("WEB-INF/platforms/test.properties"));
    }
    
    /**
     * 监听配置文件是否被更新，自动更新文件中的配置项存储到 application 变量中。
     */
    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();
    }
    
    /**
     * 判断物理文件是否已被更新
     * @param filename 物理文件名
     * @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;
        }
    }
    
    /**
     * 获取配置文件
     * @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);
    }
    
    /**
     * 从 application 取配置项的值
     * @param key 配置项的键名
     * @return 配置项的值
     */
    public String getTestProperty(String key){
        Properties prop = (Properties)context.getAttribute("test");
        if(prop==null){
            return null;
        }else{
            return (String)prop.get(key);
        }
    }

}

web.xml 配置

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

在 WEB-INF 目录下增加 platforms/test.properties 文件

name=Stephen Wong

启动应用服务器，控制台输出如下：

11:30:31,000 INFO  [TomcatDeployer] undeploy, ctxPath=/ServerTest, warUrl=.../deploy/ServerTest.war/
11:30:31,000 INFO  [[/ServerTest]] Properties listener stop .
11:30:31,000 INFO  [STDOUT] Properties listener stop .
11:30:31,046 INFO  [TomcatDeployer] deploy, ctxPath=/ServerTest, warUrl=.../deploy/ServerTest.war/
11:30:31,359 INFO  [[/ServerTest]] Properties listener start .
11:30:31,359 INFO  [STDOUT] Properties listener start .
11:30:31,375 INFO  [STDOUT] A task instance is created now.
11:30:31,390 INFO  [STDOUT] Task running
11:30:31,390 INFO  [STDOUT] 0.9924364802139768
11:30:31,390 INFO  [STDOUT] The properties file was modified.
11:30:31,390 INFO  [STDOUT] Getting properties
11:30:31,390 INFO  [STDOUT] Test value is: Stephen
11:30:46,390 INFO  [STDOUT] Task running
11:30:46,390 INFO  [STDOUT] 0.24869896604923036
11:30:46,390 INFO  [STDOUT] The properties file was not modified.
11:30:46,390 INFO  [STDOUT] Test value is: Stephen
11:31:01,390 INFO  [STDOUT] Task running
11:31:01,390 INFO  [STDOUT] 0.47994173379307203
11:31:01,390 INFO  [STDOUT] The properties file was not modified.
11:31:01,390 INFO  [STDOUT] Test value is: Stephen
11:31:16,390 INFO  [STDOUT] Task running
11:31:16,390 INFO  [STDOUT] 0.6379331056768383
11:31:16,390 INFO  [STDOUT] The properties file was modified.
11:31:16,390 INFO  [STDOUT] Getting properties
11:31:16,390 INFO  [STDOUT] Test value is: Stephen Wong
11:31:31,390 INFO  [STDOUT] Task running
11:31:31,390 INFO  [STDOUT] 0.30415561271978353
11:31:31,390 INFO  [STDOUT] The properties file was not modified.
11:31:31,390 INFO  [STDOUT] Test value is: Stephen Wong
11:31:46,390 INFO  [STDOUT] Task running
11:31:46,390 INFO  [STDOUT] 0.03696303208126983
11:31:46,390 INFO  [STDOUT] The properties file was not modified.
11:31:46,390 INFO  [STDOUT] Test value is: Stephen Wong