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A Java library for generating Universally Unique Lexicographically Sortable Identifiers (ULID)
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README.md

ULID Creator

A Java library for generating ULIDs.

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

How to Use

Create a ULID:

UUID ulid = UlidCreator.getUlid(); // 01706d6c-6aad-c795-370c-98d0be881bba

Create a ULID string:

String ulid = UlidCreator.getUlidString(); // 01E1PPRTMSQ34W7JR5YSND6B8Z

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>2.1.0</version>
</dependency>

See more options in maven.org.

Implementation

ULID

The GUIDs in this library are based on the ULID specification. The first 48 bits represent the count of milliseconds since Unix Epoch, 1 January 1970. The remaining 60 bits are generated by a secure random number generator.

Every time the timestamp changes the random part is reset to a new random value. If the current timestamp is equal to the previous one, the random bits are incremented by 1.

The default random number generator is java.security.SecureRandom.

// GUID based on ULID spec
UUID ulid = UlidCreator.getUlid();

Sequence of GUIDs based on ULID spec:

01706d6c-6aac-80bd-7ff5-f660c2dd58ea
01706d6c-6aac-80bd-7ff5-f660c2dd58eb
01706d6c-6aac-80bd-7ff5-f660c2dd58ec
01706d6c-6aac-80bd-7ff5-f660c2dd58ed
01706d6c-6aac-80bd-7ff5-f660c2dd58ee
01706d6c-6aac-80bd-7ff5-f660c2dd58ef
01706d6c-6aac-80bd-7ff5-f660c2dd58f0
01706d6c-6aac-80bd-7ff5-f660c2dd58f1
01706d6c-6aad-c795-370c-98d0be881bb8 < millisecond changed
01706d6c-6aad-c795-370c-98d0be881bb9
01706d6c-6aad-c795-370c-98d0be881bba
01706d6c-6aad-c795-370c-98d0be881bbb
01706d6c-6aad-c795-370c-98d0be881bbc
01706d6c-6aad-c795-370c-98d0be881bbd
01706d6c-6aad-c795-370c-98d0be881bbe
01706d6c-6aad-c795-370c-98d0be881bbf
            ^ look                 ^ look
                                   
|------------|---------------------|
  millisecs        randomness

ULID string

The ULID string is a sequence of 26 chars. See the ULID specification for more information.

See the section on GUIDs to know how the 128 bits are generated in this library.

// String based on ULID spec
String ulid = UlidCreator.getUlidString();

Sequence of Strings based on ULID spec:

01E1PPRTMSQ34W7JR5YSND6B8T
01E1PPRTMSQ34W7JR5YSND6B8V
01E1PPRTMSQ34W7JR5YSND6B8W
01E1PPRTMSQ34W7JR5YSND6B8X
01E1PPRTMSQ34W7JR5YSND6B8Y
01E1PPRTMSQ34W7JR5YSND6B8Z
01E1PPRTMSQ34W7JR5YSND6B90
01E1PPRTMSQ34W7JR5YSND6B91
01E1PPRTMTYMX8G17TWSJJZMEE < millisecond changed
01E1PPRTMTYMX8G17TWSJJZMEF
01E1PPRTMTYMX8G17TWSJJZMEG
01E1PPRTMTYMX8G17TWSJJZMEH
01E1PPRTMTYMX8G17TWSJJZMEJ
01E1PPRTMTYMX8G17TWSJJZMEK
01E1PPRTMTYMX8G17TWSJJZMEM
01E1PPRTMTYMX8G17TWSJJZMEN
         ^ look          ^ look
                                   
|---------|--------------|
 millisecs   randomness

How use the UlidSpecCreator directly

These are some examples of using the UlidSpecCreator to create ULID strings:

// with your custom timestamp strategy
TimestampStrategy customStrategy = new CustomTimestampStrategy();
UlidSpecCreator creator = UlidCreator.getUlidSpecCreator()
	.withTimestampStrategy(customStrategy);
String ulid = creator.createString();

// with your custom random strategy that wraps any random generator
RandomStrategy customStrategy = new CustomRandomStrategy();
UlidSpecCreator creator = UlidCreator.getUlidSpecCreator()
	.withRandomStrategy(customStrategy);
String ulid = creator.createString();

// with `java.util.Random` number generator
Random random = new Random();
UlidSpecCreator creator = UlidCreator.getUlidSpecCreator()
    .withRandomGenerator(random);
String ulid = creator.createString();

Benchmark

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

---------------------------------------------------------------------------
THROUGHPUT                         Mode  Cnt      Score     Error   Units
---------------------------------------------------------------------------
Throughput.Java_RandomBased        thrpt    5   2234,199 ±   2,844  ops/ms
Throughput.UlidCreator_Ulid        thrpt    5  19155,742 ±  22,195  ops/ms
Throughput.UlidCreator_UlidString  thrpt    5   4946,479 ±  22,800  ops/ms
---------------------------------------------------------------------------
Total time: 00:04:01
---------------------------------------------------------------------------

----------------------------------------------------------------------
AVERAGE TIME                        Mode  Cnt    Score   Error  Units
----------------------------------------------------------------------
AverageTime.Java_RandomBased        avgt    5  449,641 ± 0,994  ns/op
AverageTime.UlidCreator_Ulid        avgt    5   52,199 ± 0,185  ns/op
AverageTime.UlidCreator_UlidString  avgt    5  202,014 ± 2,111  ns/op
----------------------------------------------------------------------
Total time: 00:04:01
----------------------------------------------------------------------

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

See: uuid-creator-benchmark

Links for generators