Am 16.05.2015 um 14:21 schrieb Suliman:

The problem is that you didn't specify the API interface.

Why I should to specify API interface? It's element of good design, but why I can't create simple class without it?

This restriction has been chosen to ensure a working REST server/client
duality. By always working on an interface, both are guaranteed to work
and to result in exactly the same REST protocol. For cases where only
the server is planned to be used, the restriction could in theory be
lifted...