转自：http://www.cnblogs.com/callwangxiang/archive/2011/08/04/JavaDirectoryWatcherFileWatcher.html

package marvellousworks.practicalpattern.concept.unittest;

import java.nio.file.WatchEvent.Kind;

/**
 * 文件系统事件类型
 * @author wangxiang
 *
 */
public final class FileSystemEventArgs {
    private final String fileName;
    private final Kind<?> kind;
    
    public FileSystemEventArgs(String fileName, Kind<?> kind){
        this.fileName = fileName;
        this.kind = kind;
    }
    
    /**
     * 文件的路径
     */
    public String getFileName(){return fileName;}
    
    /**
     * 操作类型：变更、创建、删除
     */
    @SuppressWarnings("rawtypes")
    public Kind getKind(){return kind;}
}

package marvellousworks.practicalpattern.concept.unittest;

import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchEvent.Kind;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.Observable;
import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;

import static java.nio.file.StandardWatchEventKinds.*;

/**
 * 监控一个目录内文件的更新、创建和删除事件（不包括子目录）
 * 
 * 对于http://download.oracle.com/javase/tutorial/essential/io/notification.html进行了改造
 * 使其更接近.NET的DirectoryWatcher使用习惯
 * 
 * 由于java没有类似.NET源生的事件机制
 * 因此实现上采用了Java SE自带的Observer/Observable对象对外抛出“假”事件
 * 
 * 适于Java SE 7
 * 
 * @author wangxiang
 *
 */
public class DirectoryWatcher extends Observable{

    private WatchService watcher;
    private Path path;
    private WatchKey key;
    private Executor executor = Executors.newSingleThreadExecutor();
    
    FutureTask<Integer> task = new FutureTask<Integer>(
            new Callable<Integer>(){
                public Integer call() throws InterruptedException{
                    processEvents();
                    return Integer.valueOf(0);}});

    @SuppressWarnings("unchecked")
    static <T> WatchEvent<T> cast(WatchEvent<?> event) {
        return (WatchEvent<T>) event;
    }

    public DirectoryWatcher(String dir) throws IOException {
        watcher = FileSystems.getDefault().newWatchService();
        path = Paths.get(dir);
        //    监控目录内文件的更新、创建和删除事件
        key = path.register(watcher, ENTRY_MODIFY, ENTRY_CREATE, ENTRY_DELETE);
    }

    /**
     * 启动监控过程
     */
    public void execute(){
        // 通过线程池启动一个额外的线程加载Watching过程
        executor.execute(task);        
    }
    
    /**
     * 关闭后的对象无法重新启动
     * @throws IOException
     */
    public void shutdown() throws IOException {
        watcher.close();
        executor = null;
    }

    /**
     * 监控文件系统事件
     */
    void processEvents() {
        while (true) {
            // 等待直到获得事件信号
            WatchKey signal;
            try {
                signal = watcher.take();
            } catch (InterruptedException x) {
                return;
            }

            for (WatchEvent<?> event : signal.pollEvents()) {
                Kind<?> kind = event.kind();

                // TBD - provide example of how OVERFLOW event is handled
                if (kind == OVERFLOW) {
                    continue;
                }

                // Context for directory entry event is the file name of entry
                WatchEvent<Path> ev = cast(event);
                Path name = ev.context();
                notifiy(name.getFileName().toString(), kind);
            }
            //    为监控下一个通知做准备
            key.reset();
        }
    }
    
    /**
     * 通知外部各个Observer目录有新的事件更新
     */
    void notifiy(String fileName, Kind<?> kind){
        // 标注目录已经被做了更改
        setChanged();
        //     主动通知各个观察者目标对象状态的变更
        //    这里采用的是观察者模式的“推”方式
        notifyObservers(new FileSystemEventArgs(fileName, kind));
    }
}

package com.ieslab.web.tool;

import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Observable;
import java.util.Observer;
import org.junit.Assert;
import org.junit.Test;

public class DirectoryWatcherFixture {

    private static final String DIR_PATH =System.getProperty("user.dir"); 
    private static final File DIR = new File(DIR_PATH);
    private static final String SUFFIX = ".txt";
    private static final String PREFIX = "test";
    private static final int ADD_TIMES = 3;

    /**
     * 观察者
     * @author wangxiang
     *
     */
    public class Logger implements Observer{
        @Override
        public void update(Observable observable, Object eventArgs) {
            FileSystemEventArgs args = (FileSystemEventArgs) eventArgs;
            System.out.printf("%s has been %s\n", args.getFileName(), args.getKind());
            Assert.assertTrue(args.getFileName().startsWith(PREFIX));
            Assert.assertEquals(ENTRY_CREATE, args.getKind());
        }
    }
    
    @Test
    public void testWatchFile() throws IOException, InterruptedException{
        DirectoryWatcher watcher = new DirectoryWatcher(DIR_PATH);
        Logger l1 = new Logger();
        watcher.addObserver(l1);
        watcher.execute();
        
        //    创建一系列临时文件
        List<String> files = new ArrayList<>();
        for(int i=0; i<ADD_TIMES; i++){
            files.add(File.createTempFile(PREFIX, SUFFIX, DIR).toString());
        }
        
        //    延迟等待后台任务的执行
        Thread.sleep(4000);
        watcher.shutdown();
        System.out.println("finished");
    }
}