2015-10-10

监听文件变化

目录

1. 使用场景
2. 例子
3. 注意

使用场景

对于某些文件的变化进行监听操作（如IDE及各编辑器监听文件变化来进行同步，应用服务器监听如jsp、jar等文件的变化来重新部署）。
个人学习使用该API的目的是想监听功能开关配置文件，达到修改文件后，程序重新加载配置到内存的目的。

例子

import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;

public class PathsDemo {
    public static void main(String[] args){
        try {
            //The first step is to create a new WatchService by using the newWatchService method in the FileSystem class.
            WatchService watchService=FileSystems.getDefault().newWatchService();
 
            //register one or more objects with the watch service.
            //When registering an object with the watch service, you specify the types of events that you want to monitor.
            Paths.get(propertiesPath).register(watchService,  
                    StandardWatchEventKinds.ENTRY_CREATE, //A directory entry is created
                    StandardWatchEventKinds.ENTRY_DELETE, //A directory entry is deleted
                    StandardWatchEventKinds.ENTRY_MODIFY);//A directory entry is modified.
 
            while(true) 
            { 
                //Returns a queued key. If no queued key is available, this method waits.
                WatchKey key=watchService.take(); 
                for(WatchEvent<?> event:key.pollEvents()) 
                { 
                    System.out.println(event.context()+" happens "+event.kind()+" event."); 
                   //TODO business operations...
                } 
                if(!key.reset()) 
                { 
                    break; 
                } 
            } 
        } catch (Exception e) {
            System.err.println(e);
        }
    }
}

//控制台输出
config.properties happen ENTRY_MODIFY event.  

注意

Java7 才支持NIO Paths。
该API 设计不是用于索引硬盘。

Java

Java, NIO