ULID Creator

A Java library for generating ULIDs (Universally Unique Lexicographically Sortable Identifier).

• Generated in lexicographical order;
• Can be stored as a UUID/GUID;
• Can be stored as a string of 26 chars;
• Can be stored as an array of 16 bytes;
• String format is encoded to Crockford's base32;
• String format is URL safe and case insensitive.

How to Use

Create a ULID:

Ulid ulid = UlidCreator.getUlid();

Create a Monotonic ULID:

Ulid ulid = UlidCreator.getMonotonicUlid();

Maven dependency

Add these lines to your pom.xml.

<!-- https://search.maven.org/artifact/com.github.f4b6a3/ulid-creator -->
<dependency>
  <groupId>com.github.f4b6a3</groupId>
  <artifactId>ulid-creator</artifactId>
  <version>4.1.2</version>
</dependency>

See more options in maven.org.

Modularity

Module and bundle names are the same as the root package name.

• JPMS module name: com.github.f4b6a3.ulid
• OSGi symbolic name: com.github.f4b6a3.ulid

ULID

The ULID is a 128 bit long identifier. The first 48 bits represent the number of milliseconds since Unix Epoch, 1970-01-01. The remaining 80 bits are generated by a secure random number generator.

// Generate a ULID
Ulid ulid = UlidCreator.getUlid();

// Generate a ULID with a specific time
Ulid ulid = UlidCreator.getUlid(1234567890);

Sequence of ULIDs:

01EX8Y21KBH49ZZCA7KSKH6X1C
01EX8Y21KBJTFK0JV5J20QPQNR
01EX8Y21KBG2CS1V6WQCTVM7K6
01EX8Y21KB8HPZNBP3PTW7HVEY
01EX8Y21KB3HZV38VAPTPAG1TY
01EX8Y21KB9FTEJHPAGAKYG9Z8
01EX8Y21KBQGKGH2SVPQAYEFFC
01EX8Y21KBY17J9WR9KQR8SE7H
01EX8Y21KCVHYSJGVK4HBXDMR9 < millisecond changed
01EX8Y21KC668W3PEDEAGDHMVG
01EX8Y21KC53D2S5ADQ2EST327
01EX8Y21KCPQ3TENMTY1S7HV56
01EX8Y21KC3755QF9STQEV05EB
01EX8Y21KC5ZSHK908GMDK69WE
01EX8Y21KCSGJS8S1FVS06B3SX
01EX8Y21KC6ZBWQ0JBV337R1CN
         ^ look

|---------|--------------|
    time      random

Monotonic ULID

The Monotonic ULID is a 128 bit long identifier. The first 48 bits represent the number of milliseconds since Unix Epoch, 1970-01-01. The remaining 80 bits are generated by a secure random number generator.

The random component is incremented by 1 whenever the current millisecond is equal to the previous one. But when the current millisecond is different, the random component changes to another random value.

// Generate a Monotonic ULID
Ulid ulid = UlidCreator.getMonotonicUlid();

// Generate a Monotonic ULID with a specific time
Ulid ulid = UlidCreator.getMonotonicUlid(1234567890);

Sequence of Monotonic ULIDs:

01EX8Y7M8MDVX3M3EQG69EEMJW
01EX8Y7M8MDVX3M3EQG69EEMJX
01EX8Y7M8MDVX3M3EQG69EEMJY
01EX8Y7M8MDVX3M3EQG69EEMJZ
01EX8Y7M8MDVX3M3EQG69EEMK0
01EX8Y7M8MDVX3M3EQG69EEMK1
01EX8Y7M8MDVX3M3EQG69EEMK2
01EX8Y7M8MDVX3M3EQG69EEMK3
01EX8Y7M8N1G30CYF2PJR23J2J < millisecond changed
01EX8Y7M8N1G30CYF2PJR23J2K
01EX8Y7M8N1G30CYF2PJR23J2M
01EX8Y7M8N1G30CYF2PJR23J2N
01EX8Y7M8N1G30CYF2PJR23J2P
01EX8Y7M8N1G30CYF2PJR23J2Q
01EX8Y7M8N1G30CYF2PJR23J2R
01EX8Y7M8N1G30CYF2PJR23J2S
         ^ look          ^ look

|---------|--------------|
    time      random

More Examples

Create a ULID from a canonical string (26 chars):

Ulid ulid = Ulid.from("0123456789ABCDEFGHJKMNPQRS");

---

Convert a ULID into a canonical string in lower case:

String string = ulid.toLowerCase(); // 0123456789abcdefghjkmnpqrs

---

Convert a ULID into a UUID:

UUID uuid = ulid.toUuid(); // 0110c853-1d09-52d8-d73e-1194e95b5f19

---

Convert a ULID into a RFC-4122 UUID v4:

UUID uuid = ulid.toRfc4122().toUuid(); // 0110c853-1d09-42d8-973e-1194e95b5f19
                                       //               ^ UUID v4

---

Get the creation instant of a ULID:

Instant instant = ulid.getInstant(); // 2007-02-16T02:13:14.633Z

// static method
Instant instant = Ulid.getInstant("0123456789ABCDEFGHJKMNPQRS"); // 2007-02-16T02:13:14.633Z

---

A key generator that makes substitution easy if necessary:

package com.example;

import com.github.f4b6a3.ulid.UlidCreator;

public class KeyGenerator {
    public static String next() {
        return UlidCreator.getUlid().toString();
    }
}

String key = KeyGenerator.next();

---

A UlidFactory with java.util.Random:

// use a `java.util.Random` instance for fast generation
UlidFactory factory = UlidFactory.newInstance(new Random());
Ulid ulid = factory.create();

// use the factory

---

A UlidFactory with ThreadLocalRandom inside of a Supplier<byte[]>:

// use a random supplier that returns an array of 10 bytes
UlidFactory factory = UlidFactory.newInstance(() -> {
    final byte[] bytes = new byte[Ulid.RANDOM_BYTES];
    ThreadLocalRandom.current().nextBytes(bytes);
    return bytes;
});

// use the factory
Ulid ulid = factory.create();

---

Benchmark

This section shows benchmarks comparing UlidCreator to java.util.UUID.

--------------------------------------------------------------------------------
THROUGHPUT (operations/msec)            Mode  Cnt      Score     Error   Units
--------------------------------------------------------------------------------
UUID_randomUUID                        thrpt    5   2060,570 ±  37,242  ops/ms
UUID_randomUUID_toString               thrpt    5   1177,386 ±  39,803  ops/ms
UlidCreator_getUlid                    thrpt    5   2740,609 ±  86,350  ops/ms
UlidCreator_getUlid_toString           thrpt    5   2526,284 ±  56,726  ops/ms
UlidCreator_getMonotonicUlid           thrpt    5  19373,150 ± 192,402  ops/ms
UlidCreator_getMonotonicUlid_toString  thrpt    5  13269,201 ± 254,953  ops/ms
--------------------------------------------------------------------------------
Total time: 00:08:01
--------------------------------------------------------------------------------

System: JVM 8, Ubuntu 20.04, CPU i5-3330, 8G RAM.

To execute the benchmark, run ./benchmark/run.sh.

Other identifier generators

Check out the other ID generators.

• UUID Creator
• TSID Creator
• KSUID Creator