gistfile1.txt

import java.io.File;
import java.io.IOException;

public class RobustSingletonBatchJob {

	public static void main(String[] args) throws Exception 
	{
		try(FileLock lock = new FileLock(new File("dir", "file")))
		{
			if (lock.isOwnsLock()) 
			{
			// ... // do the job (may throw exceptions)
			}
		}
	}
	
	public static class FileLock implements AutoCloseable
	{
		private File file;
		private boolean ownsLock = false;		
		
		public FileLock(File file)
		{
			super();
			this.file = file;
			tryLock();
		}
		
		@Override
		public void close() 
		{
			unLock();
		}

		public boolean isOwnsLock()
		{
			return ownsLock;
		}

		private void tryLock()
		{
			try 
			{
				if (!ownsLock) 
				{
					file.getParentFile().mkdirs(); // #1 Create the lock dir if
												   // it doesn't exist
					if (file.createNewFile())
					{
						ownsLock = true;
					}
				}
			}
			catch (IOException e)
			{
				throw new RuntimeException("Failed to create lock file "
						+ file.getAbsolutePath() + " due to " + e
						+ ". Fix the problem and retry.", e); // #3 Helpful
																// error
																// message with
																// context (file
																// path)
			}
		}

		private void unLock() 
		{
			if (ownsLock)
			{
				file.delete();
				ownsLock = false;
			}
		}		
	}

}