D. Identifier Generation

The Axon Framework uses an IdentifierFactory to generate all identifiers, whether they are for events, commands or queries. The default IdentifierFactory uses randomly generated java.util.UUID based identifiers. Although they are very safe to use, the process to generate them does not excel in performance.

IdentifierFactory is an abstract factory that uses Java's ServiceLoader (since Java 6) mechanism to find the implementation to use. This means you can create your own implementation of the factory and put the name of the implementation in a file called /META-INF/services/org.axonframework.common.IdentifierFactory. Java's ServiceLoader mechanism will detect that file and attempt to create an instance of the class named inside.

There are a few requirements for the IdentifierFactory. The implementation must:

1. Have its fully qualified class name as the contents of the /META-INF/services/org.axonframework.common.IdentifierFactory file on the classpath,

2. have an accessible zero-argument constructor,

3. extend IdentifierFactory,

4. be accessible by the context classloader of the application or by the classloader that loaded the IdentifierFactory class, and must

5. Be thread-safe.