Cacher is the code snippet organizer for pro developers

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.commons.io.monitor.FileAlterationListener;
import org.apache.commons.io.monitor.FileAlterationListenerAdaptor;
import org.apache.commons.io.monitor.FileAlterationMonitor;
import org.apache.commons.io.monitor.FileAlterationObserver;

/**
 * @author Edward Beckett :: <Edward@EdwardBeckett.com>
 * @since :: 12/5/2014
 */
public class Watcher {

	private final static String WATCHDIR = "D:\\Edward\\Desktop\\watch";
	private final static File dir = new File( WATCHDIR );
	private final static ReentrantLock lock = new ReentrantLock();

	public static void main( String[] args ) throws Exception {

		FileAlterationObserver fao = new FileAlterationObserver( dir );
		final long interval = 500;
		FileAlterationMonitor monitor = new FileAlterationMonitor( interval );
		FileAlterationListener listener = new FileAlterationListenerAdaptor() {

			@Override
			public void onFileCreate( File file ) {
				try {
					System.out.println( "File created: " + file.getCanonicalPath() + " checksum: " + calcSum( file ) );
				} catch( IOException e ) {
					e.printStackTrace( System.err );
				}
			}

			@Override
			public void onFileDelete( File file ) {
				try {
					System.out.println( "File removed: " + file.getCanonicalPath() );
				} catch( IOException e ) {
					e.printStackTrace( System.err );
				}
			}

			@Override
			public void onFileChange( File file ) {
				try {
					lock.lock();
					System.out.println( file.getName() + " changed: " + " checksum: " + calcSum( file ) );
				} catch( Exception e ) {
					e.printStackTrace();
				} finally {
					lock.unlock();
				}

			}
		};
		// Add listeners...
		fao.addListener( listener );
		monitor.addObserver( fao );
		monitor.start();
	}

	public static String calcSum( File file ) {

		byte[] hashBytes = null;
		try( FileInputStream fis = new FileInputStream( file ) ) {
			MessageDigest digest = MessageDigest.getInstance( "MD5" );
			byte[] buffer = new byte[1024];
			int bytesRead = -1;

			while( ( bytesRead = fis.read( buffer ) ) != -1 ) {
				digest.update( buffer, 0, bytesRead );

			}

			hashBytes = digest.digest();

		} catch( IOException | NoSuchAlgorithmException ex ) {
			ex.printStackTrace();
		}
		return bytesToHex( hashBytes );
	}

	public static String bytesToHex( byte[] bytes ) {
		final char[] hexArray = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
		char[] hexChars = new char[bytes.length * 2];
		int v;
		for(int j = 0; j < bytes.length; j++) {
			v = bytes[j] & 0xFF;
			hexChars[j * 2] = hexArray[v >>> 4];
			hexChars[j * 2 + 1] = hexArray[v & 0x0F];
		}
		return new String( hexChars );
	}

}