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Globally Unique ID Generator

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This project is a Java implementation of the Go Lang library found here: https://github.com/rs/xid

Description

Xid is a globally unique id generator library. They are small, fast to generate and ordered.

Xid uses the Mongo Object ID algorithm to generate globally unique ids with a different serialization (base32) to make it shorter when transported as a string: https://docs.mongodb.org/manual/reference/object-id/

Xid layout
01234567891011
timerandom valueinc
  • a 4-byte value representing the seconds since the Unix epoch
  • a 5-byte random value
  • a 3-byte incrementing counter, initialized to a random value

The binary representation of the id is compatible with Mongo 12 bytes Object IDs. The string representation is using base32 hex (w/o padding) for better space efficiency when stored in that form (20 bytes). The hex variant of base32 is used to retain the sortable property of the id.

Xids simply offer uniqueness and speed, but they are not cryptographically secure. They are predictable and can be brute forced given enough time.

Features

  • Size: 12 bytes (96 bits), smaller than UUID, larger than Twitter Snowflake
  • Base32 hex encoded by default (20 chars when transported as printable string, still sortable)
  • Configuration free: there is no need to set a unique machine and/or data center id
  • K-ordered
  • Embedded time with 1 second precision
  • Unicity guaranteed for 16,777,216 (24 bits) unique ids per second and per host/process
  • Lock-free (unlike UUIDv1 and v2)

Comparison

Name Binary Size String Size Features
UUID 16 bytes 36 chars configuration free, not sortable
shortuuid 16 bytes 22 chars configuration free, not sortable
Snowflake 8 bytes up to 20 chars needs machine/DC configuration, needs central server, sortable
MongoID 12 bytes 24 chars configuration free, sortable
xid 12 bytes 20 chars configuration free, sortable

Installation

Gradle

dependencies {
    implementation 'com.github.0xshamil:java-xid:1.0.0'
}

Maven

<dependency>
  <groupId>com.github.0xshamil</groupId>
  <artifactId>java-xid</artifactId>
  <version>1.0.0</version>
</dependency>

Usage

Get Xid instance

final Xid xid = Xid.get(); 

System.out.println(xid.toString()); // 9m4e2mr0ui3e8a215n4g

as base32Hex String

final String xidStr = Xid.string(); // bt0j9l2s5bo37fcla7q0

as byte array:

final byte[] xidBytes = Xid.bytes();

to create an Xid from a specific date

final String d = "10-Aug-2020 09:43:29 +0000"; 
final String dateFormat  = "dd-MMM-yyyy HH:mm:ss Z";
Date date = new SimpleDateFormat(dateFormat).parse(d);
final Xid xid = new Xid(date);

System.out.println(xid.toString()); // bsohdgdl8njn9eimov6g
System.out.println(xid.getDate()); // Mon Aug 10 15:13:29 IST 2020
System.out.println(xid.getTimestamp()); // 1597052609

to construct back Xid from a hex string:

final Xid xid = new Xid("bsohdgdl8njn9eimov6g");

System.out.println(xid.getDate()); // Mon Aug 10 15:13:29 IST 2020
System.out.println(xid.getTimestamp()); // 1597052609

Licenses

The source code is licensed under the MIT License.