convert a uuid to biginteger

gistfile1.java

private BigInteger getBigIntegerFromUuid(UUID randomUUID) {
    ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
    bb.putLong(randomUUID.getMostSignificantBits());
    bb.putLong(randomUUID.getLeastSignificantBits());
    return new BigInteger(bb.array());
}

What if I want to get back an unsigned bitInteger value rather than 2's complement value?

The same but you can reverse this operation (and result value is much smaller):

private static BigInteger pair(UUID uuid) {
	BigInteger value1 = BigInteger.valueOf(uuid.getMostSignificantBits());
	BigInteger value2 = BigInteger.valueOf(uuid.getLeastSignificantBits());
	if (value1.compareTo(value2) < 0) {
		return value2.multiply(value2).add(value1);
	}
	return value1.multiply(value1).add(value1).add(value2);
}

Another approach using unsigned longs can be found here:
https://gist.github.com/drmalex07/9008c611ffde6cb2ef3a2db8668bc251