Globally Unique ID Generator

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

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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

0	1	2	3	4	5	6	7	8	9	10	11
time				random value					inc

• 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.