code: public static String toHex(byte[] bytes, int offset, int length) {
        return toHex(bytes, offset, length, null);
     }
docs: Encodes an array of bytes as hex symbols.
  
  @param bytes
  the array of bytes to encode
  @param offset
  the start offset in the array of bytes
  @param length
  the number of bytes to encode
  @return the resulting hex string