Version 2.1 of JAX-RS mainly targeted reactive clients, SSE, and better integration into standards such as JSON-B. Besides these, some small improvements have been added.

Reactive programming is used more and more, and, in particular, the client receives new, reactive functionality to make HTTP calls and directly returning so-called reactive types. An example for such a type is the CompletionStage type. This type is supported natively; other types and libraries can be added via extensions.

In order to make reactive calls, the rx() method of the Invocation.Builder is used.

As also shown in this book, JAX-RS 2.1 supports SSE, both on the client and on the server side. The SSE standard represents a lightweight, one-way messaging protocol that uses plain text messages over HTTP.

In order to match the usual approach of the Java EE platform, the JSON-B standard which has been added in Java EE 8 is seamlessly integrated into JAX-RS. This means that, similarly to JAXB, Java types that are used as request or response bodies, respectively, are implicitly mapped to JSON.

Similarly, the new features that are part of JSON-P 1.1 and Bean Validation 2.0 are included in JAX-RS, as well. This is possible since the specifications forward the specific functionality to the corresponding standards.

A smaller update that was incorporated into JAX-RS was the inclusion of the @PATCH annotation for the HTTP method of the same name. Although support of HTTP methods other than the provided ones was possible in JAX-RS before, it simplifies the usage for developers who require this feature.

Another small but indeed helpful improvement was to include standardized HTTP timeout methods on the JAX-RS client. The builder methods connectTimeout and readTimeout handle configured timeouts. A lot of projects require this configuration, which previously resulted in including vendor-specific features.

We have seen the implementation of these features in Chapter 3, Implementing Modern Java Enterprise Applications.