在Java中创建GUID / UUID的最佳方法有哪些?
java.util.UUID.randomUUID();
UUID.randomUUID
方法在理论上可能会返回一个重复的 UUID,但这并不是一个现实中需要担心的问题。 Oracle/OpenJDK 实现使用了一个具有密码强度的随机数生成器。考虑到 UUID 中包含如此多的位数,提供了一个天文数字范围,你的应用程序可以生成数百万个这样的值而不会出现重复。如果使用其他变量,如 [1] MAC 地址或名称和 [2] 当前日期时间作为限制条件,则进一步将碰撞的可能性降至接近零。 - Basil Bourquewhile
中生成新的ID,直到找到一个不在列表中的ID为止 :p - Nyerguds请查看随Java 5及更高版本一起捆绑的UUID类
例如:
仅通过示例扩展Mark Byers的回答:
import java.util.UUID;
public class RandomStringUUID {
public static void main(String[] args) {
UUID uuid = UUID.randomUUID();
System.out.println("UUID=" + uuid.toString() );
}
}
这取决于你想要哪种类型的UUID。
标准的Java UUID
类生成版本4(随机)UUID。(更新 - 也可以生成版本3(名称)UUID。) 它还可以处理其他变体,尽管它不能生成它们。(在这种情况下,“处理”意味着从long
,byte[]
或String
表示构造UUID
实例,并提供一些适当的访问器。)
Java UUID Generator (JUG)实现声称支持“由RFC-4122定义的所有3种‘官方’类型的UUID”...尽管RFC实际上定义了4种类型并提到了第5种类型。
如果想了解UUID类型和变体的更多信息,可以参考Wikipedia提供的良好概述,而详细信息则在RFC 4122和其他规范中。
UUID.nameUUIDFromBytes(byte[] name)
生成基于名称(版本3)的UUID。 - DennisKpublic static UUID nameUUIDFromBytes(byte[] name)
。要使用类型4,请使用public static UUID randomUUID()
。JDK类中不提供类型1。 - slartibartfastclockSequence()
的javadoc。 - Stephen C在Java中生成UUID值受到安全问题的限制,只能使用版本4(随机)。
如果你需要其他版本的UUID,一种方法是让你的Java应用程序通过调用以下内容来生成UUID,以便超出JVM:uuidgen
。uuid-ossp
扩展可以生成版本1、3和4值以及其他几种变体:uuid_generate_v1mc()
- 生成版本1 UUID,但使用随机组播MAC地址而不是计算机的真实MAC地址。uuid_generate_v5(namespace uuid, name text)
- 生成版本5 UUID,其工作方式类似于版本3 UUID,但使用SHA-1作为哈希方法。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));
}
}
}
这是输出结果:
// 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'
基于名称的UUID(v3和v5)
这个实用程序类可以生成基于名称的UUID(MD5和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) + "'");
}
}
这是输出结果:
// 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'
备用生成器
您还可以使用uuid-creator
库。请查看以下示例:
// 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);
对于许多情况,我们需要为对象提供全局UUID,特别是在事件驱动架构或事件源中,我们必须根据日期对事件进行排序,但我们不需要完整的时间戳信息。
在这种情况下,我们可以使用ULID的实现之一,它是按字典顺序可排序的。
该格式与标准UUID不同,但仍然很简单:
example value: 01AN4Z07BY79KA1307SR9X4MV3
01AN4Z07BY 79KA1307SR9X4MV3
|----------| |----------------|
Timestamp Randomness
48bits 80bits
有许多语言都有实现。例如,在Java中,有一个简单的库可以实现这个功能。
代码示例:
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()
);
@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());
}
}