Java Directory Watcher Example

Java Directory Watcher Example

There are many ways you can put watcher on the directory and if you are trying to do it through java please have an example below:

• DirectoryWatcher.java:

package com.javahonk;

import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchEvent.Kind;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;

public class DirectoryWatcher implements Runnable {

    private Path path;

    public DirectoryWatcher(Path path) {
        this.path = path;
    }

    // print the events and the affected file
    private void printEvent(WatchEvent<?> event) {
        Kind<?> kind = event.kind();
        if (kind.equals(StandardWatchEventKinds.ENTRY_CREATE)) {
            Path pathCreated = (Path) event.context();
            System.out.println("Entry created:" + pathCreated);
        } else if (kind.equals(StandardWatchEventKinds.ENTRY_DELETE)) {
            Path pathDeleted = (Path) event.context();
            System.out.println("Entry deleted:" + pathDeleted);
        } else if (kind.equals(StandardWatchEventKinds.ENTRY_MODIFY)) {
            Path pathModified = (Path) event.context();
            System.out.println("Entry modified:"+ pathModified);
        }
    }

    @Override
    public void run() {
        try {
            WatchService watchService = path.getFileSystem().newWatchService();
            path.register(watchService, StandardWatchEventKinds.ENTRY_CREATE,
                    StandardWatchEventKinds.ENTRY_MODIFY, StandardWatchEventKinds.ENTRY_DELETE);

            // loop forever to watch directory
            while (true) {
                WatchKey watchKey;
                watchKey = watchService.take(); // this call is blocking until events are present

                // poll for file system events on the WatchKey
                for (final WatchEvent<?> event : watchKey.pollEvents()) {
                    printEvent(event);
                }

                // if the watched directed gets deleted, get out of run method
                if (!watchKey.reset()) {
                    System.out.println("No longer valid");
                    watchKey.cancel();
                    watchService.close();
                    break;
                }
            }

        } catch (InterruptedException ex) {
            System.out.println("interrupted. Goodbye");
            return;
        } catch (IOException ex) {
            ex.printStackTrace();
            return;
        }
    }
}

• Test program to run the test: DirectoryWatcherTest.java:

package com.javahonk;

import java.nio.file.FileSystems;
import java.nio.file.Path;

public class DirectoryWatcherTest {
	
	public static void main(String[] args) throws InterruptedException {
        
		Path pathToWatch = FileSystems.getDefault().getPath("C:\\LAS\\JavaHonk\\New folder");
        DirectoryWatcher dirWatcher = new DirectoryWatcher(pathToWatch);
        Thread dirWatcherThread = new Thread(dirWatcher);
        dirWatcherThread.start();
        
        // interrupt the program after 60 seconds to stop it.
        Thread.sleep(60000);
        dirWatcherThread.interrupt();
    }

}

• Sample output:

• For more information please visit java documentation here