code: public static String toHexString(byte[] bytes) {
  		final int l = bytes.length;
  		final char[] out = new char[l << 1];
  
  		for (int i = 0, j = 0; i < l; i++) {
  			out[j++] = hexDigits[(0xF0 & bytes[i]) >>> 4];
  			out[j++] = hexDigits[0x0F & bytes[i]];
  		}
  		return new String(out);
  	}
docs: Converts an array of bytes in a hex string; Taken from
  org.apache.commons.codec.binary.Hex.
  @param bytes array of bytes
  @return concatenated hex representation of input byte array