ShorterUuid.java

import java.math.BigInteger;
import java.util.Collections;
import java.util.UUID;
import java.util.stream.Stream;

public class ShorterUuid {
    private static void doit() {
        String original = UUID.randomUUID().toString();
        String hex = original.replaceAll("-", "");
        String s = new BigInteger(hex, 16).toString(36);
        String unpadded = new BigInteger(s, 36).toString(16);
        StringBuilder padded = new StringBuilder(String.join("", Collections.nCopies(32, "0")).substring(unpadded.length()) + unpadded);
        Stream.of(20, 16, 12, 8).forEach(index -> padded.insert(index, "-"));
        assert original.equals(padded.toString());
    }
}