Create a GUID / UUID in Java

Preliminary steps

Ready to dive into the UUID pool? Check your setup:

• You're using Java 5 onwards, right? The UUID class is available from there.
• Don't forget to import the java.util.UUID class in your file.

UUID from Strings and NIL UUIDs

Besides randomness, you can "create" UUIDs from known string values:

UUID knownUUID = UUID.fromString("123e4567-e89b-12d3-a456-556642440000"); // Mr. Know-it-all UUID
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The Nil UUID, all zeroes, also has a special birthplace:

UUID nilUUID = new UUID(0L, 0L); // The Jon Snow of UUIDs
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RFC 4122 and UUID version saga

You can enquire UUID's version like this:

int version = uuid.version(); // So, what version are you?
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Java's UUID class meets RFC 4122 standards for universal love across different systems.

More than randomness: UUID anatomy

UUID can be created using different versions based on the strategy to ensure uniqueness:

• Version 1 UUID (MAC address + Time-based): Your ID is where and when you are + NIC :)
• Version 4 UUID (Random): Leave it to Lady Luck
• Version 5 UUID (SHA-1 Hash-based): A hashed mash-up of a namespace identifier and original value

Version 1 UUID in Java

We need an external library (like JUG - Java Uuid Generator). Let's get temporal:

UUID timeUuid = Generators.timeBasedGenerator().generate(); // "TimeLord" UUID!
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Making Version 5 UUID at Home

Java's UUID doesn't natively create Version 5 UUIDs. We need crypto:

UUID nameUUID = UUID.nameUUIDFromBytes((namespaceUUID+name).getBytes()); // Secret Agent UUID!
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Platforms beyond Java

Turns out, every system has its UUID quirks:

• Command-line: On Mac OS X, BSD, Linux — uuidgen is your friend.
• Database: Ever heard of functions like uuid_generate_v4() in PostgreSQL?
• Online: Generators like uuidgenerator.net can get you a UUID over HTTP.

Play nice with databases and web services

Need to interact with databases or web services? A UUID has got your back:

• JDBC: Fetch or store UUIDs via Java Database Connectivity.
• Web APIs: A UUID is your ticket to entities on RESTful services.

Advancing UUID usage

Working with external systems

To dunk your UUIDs in different versions that Java's UUID class doesn't natively muster, you may need to adopt alternative libraries or services.

Security aspects with UUID

Version 4 UUID is the best bet when heavy-duty UUID security is a concern. A right random number generator reinforces your UUID castle.

Be smart when storing UUIDs

When storing UUIDs in databases, mind the storage format (binary or string) and the effect on your database index performance.