Create a GUID in Java
JavaGuidJava Problem Overview
What are some of the best ways to create a GUID in Java?
Java Solutions
Solution 1 - Java
java.util.UUID.randomUUID();
Solution 2 - Java
Have a look at the UUID class bundled with Java 5 and later.
For example:
- If you want a random UUID you can use the randomUUID method.
- If you want a UUID initialized to a specific value you can use the UUID constructor or the fromString method.
Solution 3 - Java
Just to extend Mark Byers's answer with an example:
import java.util.UUID;
public class RandomStringUUID {
public static void main(String[] args) {
UUID uuid = UUID.randomUUID();
System.out.println("UUID=" + uuid.toString() );
}
}
Solution 4 - Java
It depends what kind of UUID you want.
-
The standard Java
UUIDclass generates Version 4 (random) UUIDs. (UPDATE - Version 3 (name) UUIDs can also be generated.) It can also handle other variants, though it cannot generate them. (In this case, "handle" means constructUUIDinstances fromlong,byte[]orStringrepresentations, and provide some appropriate accessors.) -
The Java UUID Generator (JUG) implementation purports to support "all 3 'official' types of UUID as defined by RFC-4122" ... though the RFC actually defines 4 types and mentions a 5th type.
For more information on UUID types and variants, there is a good summary in Wikipedia, and the gory details are in RFC 4122 and the other specifications.
Solution 5 - Java
The other Answers are correct, especially this one by Stephen C.
Reaching Outside Java
Generating a UUID value within Java is limited to Version 4 (random) because of security concerns.
If you want other versions of UUIDs, one avenue is to have your Java app reach outside the JVM to generate UUIDs by calling on:
- Command-line utility
Bundled with nearly every operating system.
For example,uuidgenfound in Mac OS X, BSD, and Linux. - Database server
Use JDBC to retrieve a UUID generated on the database server.
For example, theuuid-osspextension often bundled with Postgres. That extension can generates Versions 1, 3, and 4 values and additionally a couple variations: uuid_generate_v1mc()– generates a version 1 UUID but uses a random multicast MAC address instead of the real MAC address of the computer.uuid_generate_v5(namespace uuid, name text)– generates a version 5 UUID, which works like a version 3 UUID except that SHA-1 is used as a hashing method.- Web Service
For example, UUID Generator creates Versions 1 & 3 as well as nil values and GUID.
Solution 6 - Java
This answer contains 2 generators for random-based and name-based UUIDs, compliant with RFC-4122. Feel free to use and share.
RANDOM-BASED (v4)
This utility class that generates random-based UUIDs:
package your.package.name;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
/**
* Utility class that creates random-based UUIDs.
*
*/
public abstract class RandomUuidCreator {
private static final int RANDOM_VERSION = 4;
/**
* Returns a random-based UUID.
*
* It uses a thread local {@link SecureRandom}.
*
* @return a random-based UUID
*/
public static UUID getRandomUuid() {
return getRandomUuid(SecureRandomLazyHolder.THREAD_LOCAL_RANDOM.get());
}
/**
* Returns a random-based UUID.
*
* It uses any instance of {@link Random}.
*
* @return a random-based UUID
*/
public static UUID getRandomUuid(Random random) {
long msb = 0;
long lsb = 0;
// (3) set all bit randomly
if (random instanceof SecureRandom) {
// Faster for instances of SecureRandom
final byte[] bytes = new byte[16];
random.nextBytes(bytes);
msb = toNumber(bytes, 0, 8); // first 8 bytes for MSB
lsb = toNumber(bytes, 8, 16); // last 8 bytes for LSB
} else {
msb = random.nextLong(); // first 8 bytes for MSB
lsb = random.nextLong(); // last 8 bytes for LSB
}
// Apply version and variant bits (required for RFC-4122 compliance)
msb = (msb & 0xffffffffffff0fffL) | (RANDOM_VERSION & 0x0f) << 12; // apply version bits
lsb = (lsb & 0x3fffffffffffffffL) | 0x8000000000000000L; // apply variant bits
// Return the UUID
return new UUID(msb, lsb);
}
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;
}
// Holds thread local secure random
private static class SecureRandomLazyHolder {
static final ThreadLocal<Random> THREAD_LOCAL_RANDOM = ThreadLocal.withInitial(SecureRandom::new);
}
/**
* For tests!
*/
public static void main(String[] args) {
System.out.println("// Using thread local `java.security.SecureRandom` (DEFAULT)");
System.out.println("RandomUuidCreator.getRandomUuid()");
System.out.println();
for (int i = 0; i < 5; i++) {
System.out.println(RandomUuidCreator.getRandomUuid());
}
System.out.println();
System.out.println("// Using `java.util.Random` (FASTER)");
System.out.println("RandomUuidCreator.getRandomUuid(new Random())");
System.out.println();
Random random = new Random();
for (int i = 0; i < 5; i++) {
System.out.println(RandomUuidCreator.getRandomUuid(random));
}
}
}
This is the output:
// Using thread local `java.security.SecureRandom` (DEFAULT)
RandomUuidCreator.getRandomUuid()
'ef4f5ad2-8147-46cb-8389-c2b8c3ef6b10'
'adc0305a-df29-4f08-9d73-800fde2048f0'
'4b794b59-bff8-4013-b656-5d34c33f4ce3'
'22517093-ee24-4120-96a5-ecee943992d1'
'899fb1fb-3e3d-4026-85a8-8a2d274a10cb'
// Using `java.util.Random` (FASTER)
RandomUuidCreator.getRandomUuid(new Random())
'4dabbbc2-fcb2-4074-a91c-5e2977a5bbf8'
'078ec231-88bc-4d74-9774-96c0b820ceda'
'726638fa-69a6-4a18-b09f-5fd2a708059b'
'15616ebe-1dfd-4f5c-b2ed-cea0ac1ad823'
'affa31ad-5e55-4cde-8232-cddd4931923a'
NAME-BASED (v3 and v5)
This utility class that generates name-based UUIDs (MD5 and SHA1):
package your.package.name;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;
/**
* Utility class that creates UUIDv3 (MD5) and UUIDv5 (SHA1).
*
*/
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, String algorithm, int version) {
final byte[] hash;
final MessageDigest hasher;
try {
// Instantiate a message digest for the chosen algorithm
hasher = MessageDigest.getInstance(algorithm);
// 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);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException("Message digest algorithm not supported.");
}
}
public static UUID getMd5Uuid(String string) {
return getHashUuid(null, string, MESSAGE_DIGEST_MD5, VERSION_3);
}
public static UUID getSha1Uuid(String string) {
return getHashUuid(null, string, MESSAGE_DIGEST_SHA1, VERSION_5);
}
public static UUID getMd5Uuid(UUID namespace, String string) {
return getHashUuid(namespace, string, MESSAGE_DIGEST_MD5, VERSION_3);
}
public static UUID getSha1Uuid(UUID namespace, String string) {
return getHashUuid(namespace, string, MESSAGE_DIGEST_SHA1, 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;
}
/**
* 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) + "'");
}
}
This is the 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(): '2b098683-03c9-3ed8-9426-cf5c81ab1f9f'
HashUuidCreator.getSha1Uuid(): '1ef568c7-726b-58cc-a72a-7df173463bbb'
ALTERNATE GENERATOR
You can also use the uuid-creator library. See these examples:
// Create a random-based UUID
UUID uuid = UuidCreator.getRandomBased();
// Create a name based UUID (SHA1)
String name = "JUST_A_TEST_STRING";
UUID uuid = UuidCreator.getNameBasedSha1(name);
Project page: https://github.com/f4b6a3/uuid-creator
Solution 7 - Java
For many cases, we need global UUID for objects and especially in Event-Driven Architecture or Event Sourcing we have to sort events based on the date, but we don't need full information about timestamps.
There we can use one of the implementations of ULID which is lexicographically sortable.
The format is different from standard UUID, but is still simple:
example value: 01AN4Z07BY79KA1307SR9X4MV3
01AN4Z07BY 79KA1307SR9X4MV3
|----------| |----------------|
Timestamp Randomness
48bits 80bits
There are implementations in many languages.
For example in Java, there is simple lib for that.
Code example:
import de.huxhorn.sulky.ulid.ULID;
ULID ulid = new ULID();
// with current timestamp
String newId = ulid.nextULID();
// with selected timestamp
String newId2 = ulid.nextULID(Instant
.parse("2021-12-01T00:00:00.00Z")
.toEpochMilli()
);
With Spring you can create Bean for ULID generator as well.
@Configuration
public class UUIDGeneratorConfig {
@Bean
public ULID ulidGenerator() {
return new ULID();
}
}
@Component
public class ULIDGenerator {
private final ULID ulid;
public ULIDGenerator(ULID ulid) {
this.ulid = ulid;
}
public String generateUUID() {
return ulid.nextULID();
}
public String generateUUID(Instant timestamp) {
return ulid.nextULID(timestamp.toEpochMilli());
}
}