Kotlin-based Quarkus Extension

[Stephan Strate]

Has anyone experience with kotlin-based extensions? Any pitfalls you are aware of?

Maybe even an example extension to look at?

Thanks in advance :)

[Holly Cummins]

I have, sort of. The quarkus-pact extension isn’t written in kotlin, but the pact-jvm libraries it depends on are. 

In Quarkus 2, the kotlin language libraries are handled by the parent classloader. The parent-first-ness cascades, so I also had to declare any library which used Kotlin to parent-first, or I’d get class not found exceptions. (You can see what this looks like in https://github.com/quarkiverse/quarkus-pact/blob/quarkus-2-support/quarkus-pact-consumer/runtime/pom.xml.)

In Quarkus 3, kotlin is now no longer loaded parent-first, so the extension libraries can just be handled normally. (Sort of; in my case interactions with the JUnit framework is also forcing some parent-first-ness.) 

The quarkus-pact project is https://github.com/quarkiverse/quarkus-pact. It’s got two extensions. The consumer side, https://github.com/quarkiverse/quarkus-pact/tree/main/quarkus-pact-consumer, is probably a better example to look at because it doesn’t have the JUnit framework issues. I’ve switched main over to support Quarkus 3. To see the Quarkus 2 version, you can look at https://github.com/quarkiverse/quarkus-pact/tree/quarkus-2-support/quarkus-pact-consumer. 

I’d recommend not neglecting your integration tests. They don’t run by default in the current extension template, but I found some classloading-related problems only turned up in the integration tests. 

Cheers, 

Holly

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Holly Cummins

Senior Principal Quarkus Software Engineer, Java Champion

Red Hat 

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