Example of generating unique id's using sha256

ObjectIdUtils.java

public final class ObjectIdUtils {

    private static final Logger LOGGER = LoggerFactory.getLogger(ObjectIdUtils.class);

    private static final char[] BASE36 = {
            '0', '1', '2', '3', '4', '5',
            '6', '7', '8', '9', 'A', 'B',
            'C', 'D', 'E', 'F', 'G', 'H',
            'I', 'J', 'K', 'L', 'M', 'N',
            'O', 'P', 'Q', 'R', 'S', 'T',
            'U', 'V', 'W', 'X', 'Y', 'Z'
    };

    private ObjectIdUtils() {
    }

    public static String getId(){
        byte[] byteArray = ObjectId.get().toByteArray();
        byte[] hash = sha256(byteArray);
        return encodeAsBase36(Arrays.copyOf(hash, 7));
    }

    private static byte[] sha256(byte[] byteArray) {
        try {
            final Random rnd = new Random();
            rnd.setSeed(System.currentTimeMillis());

            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            byte[] salt = new byte[byteArray.length];
            byte[] value = byteArray;

            for(int i = 0; i < 1000; i++) {
                rnd.nextBytes(salt);
                digest.update(ObjectId.get().toByteArray());
                value = digest.digest(value);
            }
            return value;
        } catch (NoSuchAlgorithmException e) {
            LOGGER.error("This should never happen because we using SHA-256 !!!", e);
            return null;
        }
    }

    private static String encodeAsBase36(byte[] input) {
        char[] chars = new char[input.length];
        for (int i = 0; i < input.length; i++) {
            chars[i] = BASE36[(input[i] & 0xFF) % BASE36.length];
        }
        return new String(chars);
    }
}