Encode and Decode a 128-bit UUID to DICOM UID Segment

gistfile1.txt

    private static String dotEncode(long n) {
        String s = String.format("%d", n);
       if (s.startsWith("-")) {
           return ".2" + s.substring(1);
       }
       return ".1" + s;
    }

    private static long dotDecode(String s) {
        if (s.startsWith("1")) {
            return Long.parseLong(s.substring(1));
        }
        if (s.startsWith("2")) {
            return Long.parseLong("-" + s.substring(1));
        }
        return 0L;
    }

    /**
     * Convert a UUID to two long number segments in a way it will not violate their rule.
     * It decimal encodes high and low parts, and prefixes each value with 1 if it's positive
     * or 2 if it is negative. UUID rule disallows a zero after a dot.
     * It generates 42 characters or so. Limit your prefix to about 20 characters.
     *
     * @param uuidOrNull a 128-bit UUID or null to self-generate one.
     *                   leaving the . at front.
     * @return The string that looks like this .17683760201842708094.28650710562283253775 appendable this to your prefix.
     */
    public static String uuidToUid(UUID uuidOrNull) {
        final UUID uuid = uuidOrNull == null ? UUID.randomUUID() : uuidOrNull;
        long h = uuid.getMostSignificantBits();
        long lo = uuid.getLeastSignificantBits();
        return dotEncode(h) + dotEncode(lo);
    }

    /**
     * Encoded Uid fragment to UUID
     * Given the UUID fragment converted by uuidToUid plus your prefix, please give the fragment part
     * including the first dot.
     * String MUST start with a . and only have two segments like this;
     * .17683760201842708094.28650710562283253775
     * @param s String containing ONLY the encoded UID fragment like .17683760201842708094.28650710562283253775
     * @return the decoded 128-bit UUID
     */
    public static UUID uidToUuid(String s) {
        String[] t = s.split("\\.");
        long high = dotDecode(t[1]);
        long low = dotDecode(t[2]);
        return new UUID(high, low);
    }