docs: public static void appendHex(StringBuilder builder, byte b, boolean toLowerCase) {
  		final char[] toDigits = toLowerCase ? DIGITS_LOWER : DIGITS_UPPER;
  		
  		int high = (b & 0xf0) >>> 4;//高位
  		int low = b & 0x0f;//低位
  		builder.append(toDigits[high]);
  		builder.append(toDigits[low]);
  	}