How you could develop against a REST Service
WORK IN PROGRESS
Module rest-backend - src/test/demo -> EndpointRunner
Module vaadin-ui - src/main/java -> BasicTestUIRunner
The REST Endpoint will run on localhost:8080
The API-Docs for the rest endpoint are on http://localhost:8080/apidocs/
The Swagger-UI will be on http://localhost:8080/apidocs/ui/index.html
The Vaadin UI will run on localhost:9999