code: public static byte[] hexString2Bytes(String hexString) {
          if (StringKit.isBlank(hexString)) return null;
          int len = hexString.length();
          if (len % 2 != 0) {
              hexString = "0" + hexString;
              len = len + 1;
          }
          char[] hexBytes = hexString.toUpperCase().toCharArray();
          byte[] ret      = new byte[len >> 1];
          for (int i = 0; i < len; i += 2) {
              ret[i >> 1] = (byte) (hex2Dec(hexBytes[i]) << 4 | hex2Dec(hexBytes[i + 1]));
          }
          return ret;
      }
docs: hexString转byteArr
  <p>例如：</p>
  hexString2Bytes("00A8") returns { 0, (byte) 0xA8 }
  
  @param hexString 十六进制字符串
  @return 字节数组