Java Development Tools

I'm trying to create an extension in JDeveloper that creates a certain file structure. While the examples provided by Oracle provide a way to create a project, they do not show a way to create folders automatically within this project (which I need to do). I have looked around and it seems like, other than Oracle itself, there is very little documentation on extensions in general, let alone this problem. Does anyone have any insight on how to create these folders/know of a good site that might have some examples?