code: public static String generateSalt(int saltLength) {
  		StringBuilder salt = new StringBuilder(saltLength);
  		for (int i=0; i<saltLength; i++) {
  			salt.append(CHAR_ARRAY[random.nextInt(CHAR_ARRAY.length)]);
  		}
  		return salt.toString();
  	}
docs: md5 128bit 16bytes
  sha1 160bit 20bytes
  sha256 256bit 32bytes
  sha384 384bit 48bytes
  sha512 512bit 64bytes