Get all @test (TestNg) methods in external program

I have a UI (desktop app) which displays all the files with ".java" extension within a project/repository, so that a user can select these (Selected classes gets added to testng xml) and run them (desktop app runs testng xml).

My requirement is simple, I want to search for all the methods with @test annotation within a project/repository, instead of searching with file extension.

Can this be achieved by testng or java reflection ? Please suggest.

Any other suggestions/approaches are also welcome.