I might understand what you did. I have a JRDataSource with Provider and import the whole built jar then to my project via a data adapter. That produces the known ClassCastExecption, idk why though. I will try to access my DataSource with a minimal Connector written in the Studio or try out some stuff these days. I think i will respond again if i have representative results from that :)
Thx a lot for your quick answer, it's a step toward the solution, in the end maybe the only one out there i found.