Take in WSDL and create Java classes representing a web service! All you need is this handy script. And some WSDL. And the understanding of what those classes actually are (that's a work-in-progress for us).
Much of this was built using the documentation for the cxf-codegen plugin it's using.
Note that that plugin in turn is using wsdl2java, so some of their documentation may also be relevant (for example, if you want to change its behaviour slightly).
You can see some example output in this other repository.
./gradlew generate
If you want a different output directory (and maybe some other things we'll want to tweak!), look at the tasks.register block in build.grade.kts.