Generate a UUID in Java

How to Generate a UUID in Java

The Java language has built-in support for generating Version 4 UUIDs. Here's an example of how you can create a UUID in Java code.

import java.util.UUID;

class MyUuidApp {
    public static void main(String[] args) {
        UUID uuid = UUID.randomUUID();
        String uuidAsString = uuid.toString();

        System.out.println("Your UUID is: " + uuidAsString);
    }
}

Explanation

• On line #1, we import the UUID class. This class is part of the standard Java JDK. No 3rd party libraries are required.
• On line #5, the UUID class' static method, randomUUID(), is used to generate a new, version 4 UUID. The generated UUID object is stored in the variable, uuid.
• Line #6 converts the uuid object into a Java String by calling its toString() method. The String representation of a UUID looks like a standard UUID (i.e. f8c3de3d-1fea-4d7c-a8b0-29f63c4c3454). If you're going to store the UUID in a file, database or model property, or send it via an API call to a different application, you'll almost always need the String representation of the uuid object, rather than the uuid object itself.
• The output from line #8 will be something like:

  Your UUID is: f8c3de3d-1fea-4d7c-a8b0-29f63c4c3454
  

Convert from a String to a UUID in Java

Although it's rare, in some circumstances you might need to convert from a String representation of a UUID (like the one from line #6 above) back into an instance of UUID.

Java's UUID class provides for this scenario with the static method, fromString(String). You can call this method like this:

import java.util.UUID;

class MyUuidApp {
    public static void main(String[] args) {
        UUID uuid = UUID.randomUUID();
        String uuidAsString = uuid.toString();

        UUID sameUuid = UUID.fromString(uuidAsString);
        assert sameUuid.equals(uuid);
    }
}

Explanation

• Line #8 shows converting the string representation of a UUID into a Java UUID instance (sameUuid) using the fromString(String) method.
• Line #9 is included to show that the 2 UUID instances are equal.

Other Options for Generating UUIDs in Java

The uuid-creator library provides support for generating many different types of UUIDs.

For example, to generate version 7 UUIDs with this library, you can:

import com.github.f4b6a3.uuid.UuidCreator;

class MyUuidApp {
    public static void main(String[] args) {
        UUID uuid = UuidCreator.getTimeOrderedEpoch();
        String uuidAsString = uuid.toString();

        System.out.println("Your UUID is: " + uuidAsString);
    }
}

Explanation

• On line #1, we import the UuidCreator class that is part of the uuid-creator library.
• On line #5, the UuidCreator class' static method, getTimeOrderedEpoch(), is used to generate a new, version 7 UUID.
• The output from line #8 will be something like:

  Your UUID is: 018b2f19-e79e-7d6a-a56d-29feb6211b04
  

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