Restful style of API/service is very simple and easy to be consumed by everybody even there are some shortcomings. Basically, almost every language has a client that can easily talk to Restful service.
Light-rest-4j contains two different implementations based on different version of specifications. Swagger 2.0 is an older specification and OpenAPI 3.0 is a newer specification. Most of our examples are in Swagger 2.0 and some of them have been migrated to OpenAPI 3.0 spec. If you are building a new Restful service, it is highly recommended to write your spec in OpenAPI 3.0