code: public static byte[] _16_2(String hexStr) {
          if (StringUtils.isEmpty(hexStr))
              return null;
  
          byte[] result = new byte[hexStr.length() / 2];
          for (int i = 0; i < hexStr.length() / 2; i++) {
              int high = Integer.parseInt(hexStr.substring(i * 2, i * 2 + 1), 16);
              int low = Integer.parseInt(hexStr.substring(i * 2 + 1, i * 2 + 2), 16);
              result[i] = (byte) (high * 16 + low);
          }
          return result;
      }
docs: 16进制转化为 2进制
  @param hexStr 16进制字符串
  @return byte[]