Well, my question is the following: what is the difference between JAX-RSand JSR 311? Since I understand that it JAX-RSis an implementation (that is, an API) of JSR 311and JSR 311it is the specification. But I have come across APIs (like Jersey) that say they are implementations of JAX-RS, and that JAX-RSis the spec. So there is my doubt, what is each thing? And in case it's JAX-RSnot a spec, does it Jerseytake the API from JAX-RSand extend it?
A JSR is a document that contains the technical specification of a technology. Defines the standards that must be met. It can be interpreted as defining "what", not "how".
In the case of JSR 311 , this is a specification for consuming REST services from Java, commonly known as JAX-RS. Details of the interfaces provided in JAX-RS are explained here. The implementation is not defined. Note that JSR 311 points to JAX-RS version 1.x. For version 2.x there is JSR 339 .
JAX-RS 1.x can be said to be synonymous with JSR 311, while JAX-RS 2.x is synonymous with JSR 339.
It is not like this. JAX-RS is the specification, not an implementation. Of course, it provides the definition of the necessary interfaces that the implementation must have. Implementation examples of the standard are Jersey and Apache CXF .
No, Jersey (and other implementations) take the JAX-RS definitions as part of the implementation it provides, as explained in the previous paragraphs.