Is it possible to inspect the runtime classpath from an extension?

[FWest98]

To prevent an "XY problem", first some context:

In our project, we have the need for an annotation similar to @ConditionalOnClass from Spring, so an annotation that will prevent bean registration when the indicated class is not present in the (runtime) classpath.

So far, we have implemented this as a BuildCompatibleExtension, which would process our annotation and query types.ofClass() to determine whether the class would be present at runtime. This worked very well, except that it now turns out that this approach will actually not inspect the runtime classpath/index, but the deployment-phase classpath. This has now caused issues for us, where some dependencies are available in the deployment phase but not at runtime.

So now a question: is there a way to determine reliably, either through class loaders or through Jandex (or something else), whether a given class will be available at runtime?

[dmlloyd]

You might be able to use io.quarkus.bootstrap.classloading.QuarkusClassLoader#isClassPresentAtRuntime(String) for this purpose.

Some other thoughts:

All of the artifacts which are known to the build process (more or less) can be found in the application model, which can be found as part of the CurateOutcomeBuildItem from an extension build step. You can examine the flags of each dependency to know if it will be included (DependencyFlags.RUNTIME_CP is likely what you want). This is a list of artifacts and is not indexed.

I believe that the Jandex index only contains artifacts which have been identified as needing indexing, for example if there is a META-INF/beans.xml file present in the artifact.

[FWest98]

Thank you so much! The isClassPresentAtRuntime method seems to indeed do exactly what we're looking for. I did come across the QCL before, but had not looked into it properly before.