JUG is a set of Java classes for working with UUIDs: generating UUIDs using any of standard methods, outputting efficiently, sorting and so on. It generates UUIDs according to the UUID specification (RFC-4122) (also see Wikipedia UUID page for more explanation)

JUG was written by Tatu Saloranta ([email protected]) originally in 2002 and has been updated over the years. In addition, many other individuals have helped fix bugs and implement new features: please see release-notes/CREDITS for the complete list.

JUG is licensed under Apache License 2.0.

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JUG can be used as a command-line tool (via class com.fasterxml.uuid.Jug), or as a pluggable component.

Maven coordinates are:

<dependency>
  <groupId>com.fasterxml.uuid</groupId>
  <artifactId>java-uuid-generator</artifactId>
  <version>4.0.1</version>
</dependency>

The only dependency for JUG is the logging library:

• For versions up to 3.x, log4j is used, optionally (runtime dependency)
• For versions 4.x and up, slf4j API is used: logging implementation to be provided by calling application

Since version 3.2.0, JUG defines JDK9+ compatible module-info.class, with module name of com.fasterxml.uuid.

For direct downloads, check out Project Wiki.

The original use case for JUG was generation of UUID values. This is done by first selecting a kind of generator to use, and then calling its generate() method. For example:

UUID uuid = Generators.randomBasedGenerator().generate();
UUID uuid = Generators.timeBasedGenerator().generate();

If you want customize generators, you may also just want to hold on to generator instance:

TimeBasedGenerator gen = Generators.timeBasedGenerator(EthernetAddress.fromInterface());
UUID uuid = gen.generate();
UUID anotherUuid = gen.generate();

If your machine has a standard IP networking setup, the Generators.egressTimeBasedGenerator (added in JUG 4.1) factory method will try to determine which network interface corresponds to the default route for all outgoing network traffic, and use that for creating a time based generator. This is likely a good choice for common usage scenarios if you want a version 1 UUID generator:

TimeBasedGenerator gen = Generators.egressTimeBasedGenerator();
UUID uuid = gen.generate();
UUID anotherUuid = gen.generate();

Generators are fully thread-safe, so a single instance may be shared among multiple threads.

Javadocs for further information can be found from Project Wiki.

Sometimes you may want to convert from java.util.UUID into external serialization: for example, as Strings or byte arrays (byte[]). Conversion to String is easy with UUID.toString() (provided by JDK), but there is no similar functionality for converting into byte[].

But UUIDUtil class provides methods for efficient conversions:

byte[] asBytes = UUIDUtil.asByteArray(uuid);
// or if you have longer buffer already
byte[] outputBuffer = new byte[1000];
// append at position #100
UUIDUtil.toByteArray(uuid, outputBuffer, 100);

UUID values are often passed as java Strings or byte[]s (byte arrays), and conversion is needed to get to actual java.util.UUID instances. JUG has optimized conversion functionality available via class UUIDUtil (package com.fasterxml.uuid.impl), used as follows:

UUID uuidFromStr = UUIDUtil.uuid("ebb8e8fe-b1b1-11d7-8adb-00b0d078fa18");
byte[] rawUuidBytes = ...; // byte array with 16 bytes
UUID uuidFromBytes = UUIDUtil.uuid(rawUuidBytes)

Note that while JDK has functionality for constructing UUID from String, like so:

UUID uuidFromStr = UUID.fromString("ebb8e8fe-b1b1-11d7-8adb-00b0d078fa18");

it is rather slower than JUG version: for more information, read Measuring performance of Java UUID.fromString().

JUG jar built under target/:

target/java-uuid-generator-4.1.1-SNAPSHOT.jar

can also be used as a simple Command-line UUID generation tool.

To see usage you can do something like:

java -jar target/java-uuid-generator-4.1.1-SNAPSHOT.jar

and get full instructions, but to generate 5 Random-based UUIDs, you would use:

java -jar target/java-uuid-generator-4.1.1-SNAPSHOT.jar -c 5 r

(where -c (or --count) means number of UUIDs to generate, and r means Random-based variant)

NOTE: this functionality is included as of JUG 4.1 -- with earlier versions you would need a bit longer invocation as Jar metadata did not specify "Main-Class". If so, you would need to use

java -cp target/java-uuid-generator-4.1.1-SNAPSHOT.jar com.fasterxml.uuid.Jug -c 5 r

JUG versions 3.1 and later require JDK 1.6 to work, mostly to be able to access local Ethernet MAC address. Earlier versions (3.0 and before) worked on 1.4 (which introduced java.util.UUID).

JDK's java.util.UUID has flawed implementation of compareTo(), which uses naive comparison of 64-bit values. This does NOT work as expected, given that underlying content is for all purposes unsigned. For example two UUIDs:

7f905a0b-bb6e-11e3-9e8f-000000000000
8028f08c-bb6e-11e3-9e8f-000000000000

would be ordered with second one first, due to sign extension (second value is considered to be negative, and hence "smaller").

Because of this, you should always use external comparator, such as com.fasterxml.uuid.UUIDComparator, which implements expected sorting order that is simple unsigned sorting, which is also same as lexicographic (alphabetic) sorting of UUIDs (when assuming uniform capitalization).

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There are many other publicly available UUID generators. For example:

• Apache Commons IO has UUID generator
• eaio-uuid
• JDK has included java.util.UUID since 1.4, but omits generation methods (esp. time/location based ones), has sub-standard performance for many operations and implements comparison in useless way
• ohannburkard.de UUID generator

Note that although some packages claim to be faster than others, it is not clear whether:

1. Claims have been properly verified (or, if they have, can be independently verified), AND
2. It is not likely that performance differences truly matter: JUG, for example, can generate a millions of UUID per second per core (sometimes hitting the theoretical limit of 10 million per second) -- and it seems unlikely that generation will be bottleneck for about any use case

so it is often best to choose based on stability of packages and API.