// files/PathWatcher.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// {ExcludeFromGradle}
import java.io.IOException;
import java.nio.file.*;
import static java.nio.file.StandardWatchEventKinds.*;
import java.util.concurrent.*;

public class PathWatcher {
 static Path test = Paths.get("test");
 static void delTxtFiles() {
 try {
 Files.walk(test)
 .filter(f ->
 f.toString().endsWith(".txt"))
 .forEach(f -> {
 try {
 System.out.println("deleting " + f);
 Files.delete(f);
 } catch(IOException e) {
 throw new RuntimeException(e);
 }
 });
 } catch(IOException e) {
 throw new RuntimeException(e);
 }
 }
 public static void
 main(String[] args) throws Exception {
 Directories.refreshTestDir();
 Directories.populateTestDir();
 Files.createFile(test.resolve("Hello.txt"));
 WatchService watcher =
 FileSystems.getDefault().newWatchService();
 test.register(watcher, ENTRY_DELETE);
 Executors.newSingleThreadScheduledExecutor()
 .schedule(
 PathWatcher::delTxtFiles,
 250, TimeUnit.MILLISECONDS);
 WatchKey key = watcher.take();
 for(WatchEvent evt : key.pollEvents()) {
 System.out.println(
 "evt.context(): " + evt.context() +
 "\nevt.count(): " + evt.count() +
 "\nevt.kind(): " + evt.kind());
 System.exit(0);
 }
 }
}
/* Output:
deleting test\bag\foo\bar\baz\File.txt
deleting test\bar\baz\bag\foo\File.txt
deleting test\baz\bag\foo\bar\File.txt
deleting test\foo\bar\baz\bag\File.txt
deleting test\Hello.txt
evt.context(): Hello.txt
evt.count(): 1
evt.kind(): ENTRY_DELETE
*/