Generate name-based UUID in Java

HashUuidCreator.java

package your.package.name;

import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;

/**
 * A UUID generator that creates hash-based or name-based UUIDs (MD5 and SHA-1).
 *
 * RFC-4122 compliant.
 *
 * Tags: uuid guid uuid-generator guid-generator generator name hash md5 sha1 rfc4122 rfc-4122
 *
 * @author: Fabio Lima 2020
 */
public class HashUuidCreator {

	// Domain Name System
	public static final UUID NAMESPACE_DNS = new UUID(0x6ba7b8109dad11d1L, 0x80b400c04fd430c8L);
	// Uniform Resource Locator
	public static final UUID NAMESPACE_URL = new UUID(0x6ba7b8119dad11d1L, 0x80b400c04fd430c8L);
	// ISO Object ID
	public static final UUID NAMESPACE_ISO_OID = new UUID(0x6ba7b8129dad11d1L, 0x80b400c04fd430c8L);
	// X.500 Distinguished Name
	public static final UUID NAMESPACE_X500_DN = new UUID(0x6ba7b8149dad11d1L, 0x80b400c04fd430c8L);

	private static final int VERSION_3 = 3; // UUIDv3 MD5
	private static final int VERSION_5 = 5; // UUIDv5 SHA1

	private static final String MESSAGE_DIGEST_MD5 = "MD5"; // UUIDv3
	private static final String MESSAGE_DIGEST_SHA1 = "SHA-1"; // UUIDv5

	private static UUID getHashUuid(UUID namespace, String name, MessageDigest hasher, int version) {

		final byte[] hash;

		// Insert name space if NOT NULL
		if (namespace != null) {
			hasher.update(toBytes(namespace.getMostSignificantBits()));
			hasher.update(toBytes(namespace.getLeastSignificantBits()));
		}

		// Generate the hash
		hash = hasher.digest(name.getBytes(StandardCharsets.UTF_8));

		// Split the hash into two parts: MSB and LSB
		long msb = toNumber(hash, 0, 8); // first 8 bytes for MSB
		long lsb = toNumber(hash, 8, 16); // last 8 bytes for LSB

		// Apply version and variant bits (required for RFC-4122 compliance)
		msb = (msb & 0xffffffffffff0fffL) | (version & 0x0f) << 12; // apply version bits
		lsb = (lsb & 0x3fffffffffffffffL) | 0x8000000000000000L; // apply variant bits

		// Return the UUID
		return new UUID(msb, lsb);
	}

	public static UUID getMd5Uuid(String string) {
		return getHashUuid(null, string, Md5HasherLazyHolder.INSTANCE, VERSION_3);
	}

	public static UUID getSha1Uuid(String string) {
		return getHashUuid(null, string, Sha1HasherLazyHolder.INSTANCE, VERSION_5);
	}

	public static UUID getMd5Uuid(UUID namespace, String string) {
		return getHashUuid(namespace, string, Md5HasherLazyHolder.INSTANCE, VERSION_3);
	}

	public static UUID getSha1Uuid(UUID namespace, String string) {
		return getHashUuid(namespace, string, Sha1HasherLazyHolder.INSTANCE, VERSION_5);
	}

	private static byte[] toBytes(final long number) {
		return new byte[] { (byte) (number >>> 56), (byte) (number >>> 48), (byte) (number >>> 40),
				(byte) (number >>> 32), (byte) (number >>> 24), (byte) (number >>> 16), (byte) (number >>> 8),
				(byte) (number) };
	}

	private static long toNumber(final byte[] bytes, final int start, final int length) {
		long result = 0;
		for (int i = start; i < length; i++) {
			result = (result << 8) | (bytes[i] & 0xff);
		}
		return result;
	}

	private static class Md5HasherLazyHolder {
		static final MessageDigest INSTANCE = getInstance();

		private static MessageDigest getInstance() {
			try {
				return MessageDigest.getInstance(MESSAGE_DIGEST_MD5);
			} catch (NoSuchAlgorithmException e) {
				throw new RuntimeException("Message digest algorithm not supported.");
			}
		}
	}

	private static class Sha1HasherLazyHolder {
		static final MessageDigest INSTANCE = getInstance();

		private static MessageDigest getInstance() {
			try {
				return MessageDigest.getInstance(MESSAGE_DIGEST_SHA1);
			} catch (NoSuchAlgorithmException e) {
				throw new RuntimeException("Message digest algorithm not supported.");
			}
		}
	}

	/**
	 * For tests!
	 */
	public static void main(String[] args) {

		String string = "JUST_A_TEST_STRING";
		UUID namespace = UUID.randomUUID(); // A custom name space

		System.out.println("Java's generator");
		System.out.println("UUID.nameUUIDFromBytes():      '" + UUID.nameUUIDFromBytes(string.getBytes()) + "'");
		System.out.println();
		System.out.println("This generator");
		System.out.println("HashUuidCreator.getMd5Uuid():  '" + HashUuidCreator.getMd5Uuid(string) + "'");
		System.out.println("HashUuidCreator.getSha1Uuid(): '" + HashUuidCreator.getSha1Uuid(string) + "'");
		System.out.println();
		System.out.println("This generator WITH name space");
		System.out.println("HashUuidCreator.getMd5Uuid():  '" + HashUuidCreator.getMd5Uuid(namespace, string) + "'");
		System.out.println("HashUuidCreator.getSha1Uuid(): '" + HashUuidCreator.getSha1Uuid(namespace, string) + "'");
	}
}

//  OUTPUT:
//
//	Java's generator
//	UUID.nameUUIDFromBytes():      '9e120341-627f-32be-8393-58b5d655b751'
//
//	This generator
//	HashUuidCreator.getMd5Uuid():  '9e120341-627f-32be-8393-58b5d655b751'
//	HashUuidCreator.getSha1Uuid(): 'e4586bed-032a-5ae6-9883-331cd94c4ffa'
//
//	This generator WITH name space
//	HashUuidCreator.getMd5Uuid():  'b5ac8a9a-096f-3256-8b6b-25d382116360'
//	HashUuidCreator.getSha1Uuid(): '8b25a9ec-e127-53fd-b473-c91a69e68853'
//