164 lines
4.4 KiB
Markdown
164 lines
4.4 KiB
Markdown
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# ulid-creator
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A Java library for generating and handling ULIDs - _Universally Unique Lexicographically Sortable Identifiers_.
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How to Use
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------------------------------------------------------
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Create a ULID:
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```java
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String ulid = UlidCreator.getUlid();
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```
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Create a fast ULID:
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```java
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String ulid = UlidCreator.getFastUlid();
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```
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Create a ULID as GUID object:
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```java
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UUID ulid = UlidCreator.getGuid();
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```
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Create a fast ULID as GUID object:
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```java
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UUID ulid = UlidCreator.getFastGuid();
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```
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Create a ULID as byte sequence:
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```java
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byte[] ulid = UlidCreator.getBytes();
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```
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Create a fast ULID as byte sequence:
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```java
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byte[] ulid = UlidCreator.getFastBytes();
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```
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### Maven dependency
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Add these lines to your `pom.xml`.
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```xml
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<!-- https://search.maven.org/artifact/com.github.f4b6a3/ulid-creator -->
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<dependency>
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<groupId>com.github.f4b6a3</groupId>
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<artifactId>ulid-creator</artifactId>
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<version>1.0.0</version>
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</dependency>
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```
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See more options in [maven.org](https://search.maven.org/artifact/com.github.f4b6a3/ulid-creator) and [mvnrepository.com](https://mvnrepository.com/artifact/com.github.f4b6a3/ulid-creator).
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Implementation
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------------------------------------------------------
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### ULID
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The ULID is a unique and sortable 26 char sequence. See the [ULID specification](https://github.com/ulid/spec) for more information.
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See the section on GUIDs to know how the 128 bits are generated in this library.
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```java
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// ULIDs
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String ulid = UlidCreator.getUlid();
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```
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Examples of ULIDs:
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```text
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01E1PPRTMSQ34W7JR5YSND6B8T
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01E1PPRTMSQ34W7JR5YSND6B8V
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01E1PPRTMSQ34W7JR5YSND6B8W
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01E1PPRTMSQ34W7JR5YSND6B8X
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01E1PPRTMSQ34W7JR5YSND6B8Y
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01E1PPRTMSQ34W7JR5YSND6B8Z
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01E1PPRTMSQ34W7JR5YSND6B90
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01E1PPRTMSQ34W7JR5YSND6B91
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01E1PPRTMTYMX8G17TWSJJZMEE < millisecond changed
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01E1PPRTMTYMX8G17TWSJJZMEF
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01E1PPRTMTYMX8G17TWSJJZMEG
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01E1PPRTMTYMX8G17TWSJJZMEH
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01E1PPRTMTYMX8G17TWSJJZMEJ
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01E1PPRTMTYMX8G17TWSJJZMEK
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01E1PPRTMTYMX8G17TWSJJZMEM
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01E1PPRTMTYMX8G17TWSJJZMEN
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^ look ^ look
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|---------|--------------|
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milli randomness
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```
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### GUID
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The GUIDs in this library are based on the ULID specification <sup>[9]</sup>. 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.
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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.
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The default random number generator is `SecureRandom`, but it's possible to use any RNG that extends `Random`.
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```java
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// GUID based on ULID spec
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UUID guid = UlidCreator.getGuid();
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```
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Examples of GUIDs based on ULID spec:
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```text
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01706d6c-6aac-80bd-7ff5-f660c2dd58ea
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01706d6c-6aac-80bd-7ff5-f660c2dd58eb
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01706d6c-6aac-80bd-7ff5-f660c2dd58ec
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01706d6c-6aac-80bd-7ff5-f660c2dd58ed
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01706d6c-6aac-80bd-7ff5-f660c2dd58ee
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01706d6c-6aac-80bd-7ff5-f660c2dd58ef
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01706d6c-6aac-80bd-7ff5-f660c2dd58f0
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01706d6c-6aac-80bd-7ff5-f660c2dd58f1
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01706d6c-6aad-c795-370c-98d0be881bb8 < millisecond changed
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01706d6c-6aad-c795-370c-98d0be881bb9
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01706d6c-6aad-c795-370c-98d0be881bba
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01706d6c-6aad-c795-370c-98d0be881bbb
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01706d6c-6aad-c795-370c-98d0be881bbc
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01706d6c-6aad-c795-370c-98d0be881bbd
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01706d6c-6aad-c795-370c-98d0be881bbe
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01706d6c-6aad-c795-370c-98d0be881bbf
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^ look ^ look
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|------------|---------------------|
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millisecs randomness
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```
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#### How use the `GuidCreator` directly
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These are some examples of using the `GuidCreator` to create ULIDs:
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```java
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// with the default random generator (java.security.SecureRandom)
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String ulid = UlidCreator.getGuidCreator().createUlid();
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// with java random generator (java.util.Random)
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String ulid = UlidCreator.getGuidCreator()
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.withRandomGenerator(new Random())
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.createUlid();
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// with fast random generator (Xorshift128Plus)
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String ulid = UlidCreator.getGuidCreator()
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.withFastRandomGenerator()
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.createUlid();
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// with fast random generator (Xorshift128Plus with salt)
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int salt = (int) FingerprintUtil.getFingerprint();
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Random random = new Xorshift128PlusRandom(salt);
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String ulid = UlidCreator.getGuidCreator()
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.withRandomGenerator(random)
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.createUlid();
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```
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If you use the `GuidCreator` directly, you need do handle the `UlidCreatorException`, in the case that too many ULIDs are requested within the same millisecond.
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