Hi Vincenzo,
Sorry for late response.
i have made one sample application of RESTAPI in Java. there no Spring or nor Struts.
It's Jersey API based Sample .
I share link here you can find full source code and get REST API. which you can use via SAPUI5 easily.That include all necessary library. It's working source code.
https://github.com/riaconsultant/Restful
Just download and Import that project into your eclipse and run into Tomcat 7.0 version.
http://localhost:8080/SampleRest/service -- GET
http://localhost:8080/SampleRest/service/todos/12132432342 -- GET
I think that's help you more.
Regards
Manoj