An example from the docs:
JsonArray value = Json.createArrayBuilder()
.add("number", "212 555-1234"))
.add("number", "646 555-4567"))
Java EE is a specification; it has no implementation. It relies on third-parties to implement the specification.
javax.json package is part (or will eventually be part of) java EE. Therefore, including this jar will only provide you with the interface to a json api. You will be required to provide an implementation at runtime for it to work. Usually, your code should be agnostic to the implementation even if, in the fact, this is easier said than done.