code: public static String getRandomFilename(final String prefix) {
  		final Random rnd = new Random();
  		final StringBuilder stringBuilder = new StringBuilder(prefix);
  
  		for (int i = 0; i < RANDOM_FILE_NAME_LENGTH; i++) {
  			stringBuilder.append(ALPHABET[rnd.nextInt(ALPHABET.length)]);
  		}
  
  		return stringBuilder.toString();
  	}
docs: Constructs a random filename with the given prefix and
  a random part generated from hex characters.
  
  @param prefix
  the prefix to the filename to be constructed
  @return the generated random filename with the given prefix