开发过程中我们需要对某个目录或者某个文件做监听，当文件的创建、修改、删除时执行某些操作。
除了使用定时任务来定时监听之外，还可以使用apache.commons.io包的监听工具类。

import org.apache.commons.io.monitor.FileAlterationListener;
import org.apache.commons.io.monitor.FileAlterationMonitor;
import org.apache.commons.io.monitor.FileAlterationObserver;

import java.io.File;

public class FileMonitor {
    private FileAlterationMonitor monitor;

    public FileMonitor(long interval) {
        monitor = new FileAlterationMonitor(interval);
    }

    /**
     * 给文件添加监听
     *
     * @param path         文件路径
     * @param listener 文件监听器
     */
    public void monitor(String path, FileAlterationListener listener) {
        FileAlterationObserver observer = new FileAlterationObserver(new File(path));
        monitor.addObserver(observer);
        observer.addListener(listener);
    }

    public void stop() throws Exception {
        monitor.stop();
    }

    public void start() throws Exception {
        monitor.start();
    }


    public static void main(String[] args) throws Exception {
        FileMonitor fileMonitor = new FileMonitor(1000);
        fileMonitor.monitor("F:\\test\\", new FileTail()); // FileTail、FileListener
        fileMonitor.start();
    }
}

import org.apache.commons.io.monitor.FileAlterationListenerAdaptor;
import org.apache.commons.io.monitor.FileAlterationObserver;

import java.io.File;

public class FileListener extends FileAlterationListenerAdaptor {

    @Override
    public void onStart(FileAlterationObserver observer) {
        super.onStart(observer);
        //System.out.println("onStart");
    }


    @Override
    public void onDirectoryCreate(File directory) {
        System.out.println("新建：" + directory.getAbsolutePath());
    }

    @Override
    public void onDirectoryChange(File directory) {
        System.out.println("修改：" + directory.getAbsolutePath());
    }

    @Override
    public void onDirectoryDelete(File directory) {
        System.out.println("删除：" + directory.getAbsolutePath());
    }

    @Override
    public void onFileCreate(File file) {
        String compressedPath = file.getAbsolutePath();
        System.out.println("新建：" + compressedPath);
        if (file.canRead()) {
            System.out.println("文件变更，进行处理");
        }
    }

    @Override
    public void onFileChange(File file) {
        String compressedPath = file.getAbsolutePath();
        System.out.println("修改：" + compressedPath);
    }

    @Override
    public void onFileDelete(File file) {
        System.out.println("删除：" + file.getAbsolutePath());
    }

    @Override
    public void onStop(FileAlterationObserver observer) {
        super.onStop(observer);
        //System.out.println("onStop");
    }
}