[jax-rs-spec users] Hypermedia API

From: Markus KARG <>
Date: Wed, 10 Dec 2014 22:36:49 +0100


you asked for statements on the field of hypermedia and reactive. I will
take the chance to start discussion hereby on the field of hypermedia and
provide a starter for reactive in a separate thread.

Some weeks back I gave a lecture on JAX-RS 2.0 big picture at JUG Stuttgart,
just as I did infrequently at other events before. I'd like to describe the
reactions as those were stereotypical, independent of audience, location and
date. People where convinced by the very clean separation of concerns
(application made up from pure domain objects, technical aspects separated
from domain model), and the mostly declarative programming style (simply
adding annotations to declare needs, engine solves the needs "under the
hood" using a sophisticated and extensible technical infrastructure). But
when the presentation came to hypermedia support, they were some kind of
shocked by the mostly algorithmic coding style needed to make it work,
voiding the aforementioned separation of concerns and declarative code
style. While the existing API clearly is a foundation to achieve at least
"something", real HATEOAS becomes a hack with the existing low level support
only. Code gets cluttered with old-style techno-punk, which is hard to read
and understand. This is due to the lack of a declarative way to tell the
infrastructure how to make up the links from application domain state, and
how to provide the links to an entitiy provider so he can merge them into
the wire-level representation. Certainly everbody would vote for a
declarative kind of solution fitting into the existing infrastructure. On
the other hand, nobody (yes, really zero) people wanted to agree that they
have a REAL NEED for HATEOAS (hence, neither for an explicit HATEOAS API) as
100% of all attendees admitted that their recent and current RESTful
projects are on level 1 or 2 of the REST Maturity Model only, and that the
largest obstacle to level 3 is not a techical issue (hence not a missing
explicit HATEOAS API) but the fact that HATEOS as a paradigm simply is not
well understood by most of them and / or they do not see the actual benefit
of HATEOAS in the real world: It wouldn't pay off, but it would be cool, to
sum it up.

So the question is: Is HATEOAS commonly understood well enough that it makes
actual sense to provide an explicit API for it, or does it make sense to
make an API even when it is not? And if we define an API, do we all agree
that it should support the separation of concerns and declarative style that
is typical for JAX-RS?

I think without an agreement on that general topics, it wouldn't be a good
idea to discuss any kind of details of API proposals in the area of HATEOAS.

Bill and Sergey, what's your opinion on that?


-----Original Message-----
From: Santiago Pericas-Geertsen []

Sent: Mittwoch, 10. Dezember 2014 20:03
Cc: Marek Potociar
Subject: Welcome to the JAX-RS 2.1 EG

Hello Experts,

 Welcome to the JAX-RS 2.1 (JSR 370) expert group!

 This is the official mailing list for the JSR. Note that the old mailing
list for JAX-RS 2.0 (JSR 339) is still available for 2.0 matters.

 Before we start any discussions, I would like everyone to take a couple of
minutes and read the JSR description one more time to make sure we are all
on the same page ;)

2.1 Please describe the proposed Specification:

Server-Sent Events (SSE) is a new technology defined as part of the HTML5
set of recommendations for a client (e.g., a browser) to automatically get
updates from a server via HTTP. It is commonly employed for one-way
streaming data transmissions in which a server updates a client periodically
or every time an event takes place.

JAX-RS 2.0 introduced the notion of asynchronous processing for both the
client and the server APIs. However, asynchronous processing alone cannot
deliver on all the promises of a modern architecture without the help of
non-blocking I/O. If only blocking I/O is available, asynchronous processing
simply pushes the problem from one thread to the next --this is akin to
borrowing from a person to pay another, the problem is not really solved,
only deferred. Thus, support for non-blocking I/O is necessary to achieve
high throughput and efficiently manage resources like threads.

In summary, the following is a list of the tasks in scope for JAX-RS 2.1:

 * Adding support for SSE.
 * Improving integration with CDI.
 * Exploring support for non-blocking I/O in providers (filters,
interceptors, etc.).
 * Evaluating ways in which declarative security can be supported either
directly in this JSR or by leveraging other EE-platform JSRs.
 * Making JAXB conditional on runtimes where it is available.
 * Providing integration with JSON-B.
 * Building upon the hypermedia API added in version 2.0.
 * Investigating the reactive programming paradigm as a way to improve the
JAX-RS asynchronous client API.
 * Evaluating any requirements necessary to support the use of JAX-RS
resource classes as controllers in the MVC 1.0 JSR.

 Some useful links:

 [JAX-RS Spec] [JIRA for 2.1]
 [E-mail Archives]

 As before, all of our discussions will be conducted using the expert's
alias and (automatically) CCed to the user's alias.

 Some of the 2.1 tasks above require coordination with other specifications
(JSON-B, Security), so these tasks will tackled later on in the process.

 We have tentatively selected 2 topics to start our discussions, both of
which require some investigation, these are: hypermedia improvements and
reactive programming. If you have any suggestions/comments/concerns about
these two topics, feel free to start a discussion about them. We will be
sending some more info as well in the upcoming weeks.

 Looking forward to working with all of you!

Santiago Pericas-Geertsen
Marek Potociar
JSR 370 Spec Leads