How to properly fix 'Resource was located via Classloader'

[Maarten Daalder (ISAAC Software Solutions)]

Hi,

We have multiple modules that share resources (mostly images and css) which are placed in their own module.
This module has a *.gwt.xml file but no entrypoint and everything compiles as it should, except we get these warnings:

[WARN] Resource '{}' was located via ClassLoader. As a result changes in that resource will not be reflected in per-file recompiles.
It should be registered via  <source /> or <resource /> entry in your .gwt.xml. In a future version of GWT, we will remove this fallback and your application will stop compiling

These resources are currently located in src/main/resources/images/.../*.png where it all works.
But if I move them (and update references to them) to src/main/java/package/where/resourcebundle/class/lives the warnings doesn't go away.

I've tried several other variants with or without absolute references, either it won't compile or it will still give the warnings.
I suspect this is due to our multi-module maven setup, but I find it unclear how to resolve, maybe copy resources to the projects that use them? But that isn't really maintainable (there are occasional changes to the styling).
I could possibly use maven to do that during the build, but I'm unsure if that would solve it.

With kind regards,
Maarten Daalder
ISAAC