code: public static String generateString(int length) {
  
  		if (length <= 0 || length > 100) {
  			throw new IllegalArgumentException("Can't generate random id with length: " + length);
  		}
  
  		SecureRandom random = new SecureRandom();
  		StringBuilder sb = new StringBuilder(length);
  		for (int i = 0; i < length; i++) {
  			sb.append(ELEMENTS.charAt(random.nextInt(ELEMENTS.length())));
  		}
  
  		return sb.toString();
  	}
docs: Generates random string from ELEMENTS set of chars and numbers
  
  @param length desired length of key greater than 0
  @return random string of desired length (min 1, max 100 characters long)