public byte[] encoder(Long obj, int maxwidth) throws Exception {

   if (obj == null) {

    return new byte[] {};

   }

   if (maxwidth > 8) {

    return new byte[] {};

   }

   long value = obj.longValue();

   byte[] b = new byte[maxwidth];

   for (int i = 0; i < maxwidth; i++) {

    b[i] = (byte) ((value >>> ((maxwidth - 1) * 8 - i * 8)) & 0xFF);

   }

   return b;

  }