Directory Watcher

A recursive directory watcher utility for JDK 8+, along with a native OS X implementation of the WatchService.

Getting started

First add the dependency for your preferred build system.

SBT

libraryDependencies += "io.methvin" % "directory-watcher" % "0.2.2"

Maven

<dependency>
    <groupId>io.methvin</groupId>
    <artifactId>directory-watcher</artifactId>
    <version>0.2.2</version>
</dependency>

API

Use DirectoryWatcher.create to create a new watcher, then use either watch() to block the current thread while watching or watchAsync() to watch in another thread. This will automatically detect Mac OS X and provide a native implementation based on the Carbon File System Events API.

Example

package com.example;

import java.io.IOException;
import java.nio.file.Path;

import io.methvin.watcher.DirectoryChangeListener;
import io.methvin.watcher.DirectoryWatcher;

import static io.methvin.watcher.DirectoryChangeEvent.EventType.*;

public class DirectoryWatchingUtility {

  private final Path pathToWatch;
  private final DirectoryWatcher watcher;

  public DirectoryWatchingUtility(Path directoryToWatch) {
    this.directoryToWatch = directoryToWatch;
    this.watcher = DirectoryWatcher.create(directoryToWatch, event -> {
      switch (event.eventType()) {
        case CREATE: /* file created */; break;
        case MODIFY: /* file modified */; break;
        case DELETE: /* file deleted */; break;
      }
    });
  }

  public void stopWatching() {
    watcher.close();
  }

  public CompletableFuture<Void> watch() {
    // you can also use watcher.watch() to block the current thread
    return watcher.watchAsync();
  }
}

Implementation differences

The Mac OS X implementation returns the full absolute path of the file in its change notifications, so the returned path does not need to be resolved against the WatchKey. The DirectoryWatcher abstracts away the details of that though.

Credits

Large parts of this code are taken from https://github.com/takari/directory-watcher/, which is also licensed under the Apache 2 license. The library has been updated to make it more idiomatic Java 8 style and to remove some of the special cases.