Hi
"> Summary: cxf supporting REST means that there is a
way to program servants to react to HTTP as an application
protocol, rather than as a layered protocol.
+1 to what Oisin said there. It captures the key requirement in a single
sentence.
"However, there's more as well -- REST also requires supporting navigation of
application state via hyperlinks, which means that CXF has to enable
and perhaps help the server-side application to generate the URLs
required to identify new resources that it creates and tie servants/
implementations to them."
+1 too. Depending on the content type a client expects there should be a way to convert a response source into a navigatble HTML for
ex. Perhaps it's a job for a custom handler. I'm not sure how this can be generalized. It's also still probably a job for the top
level resource provider implementation to ensure an (XML) source it returns is navigatable.
Interesting thing here is how a client can use a navigatable XML. IMHO REST approach is still used by (arguably) a minority of
projects where it can be a better fit is that it requres what can be thought as a difficult programming model : do HTTP invocation,
check response codes, parse XML manually, etc...
JAX-WS can somehow make it easier by relying on JAXB when possible. However it's likely many would still be quite more comfortable
with stubs which will do the 'difficult' job.
Please have a look at
http://weblogs.java.net/blog/mhadley/archive/2006/05/index.html
and
http://weblogs.java.net/blog/mhadley/archive/2006/08/index.html
If cxf supported this client-side mode of working with HTTP-based services (in addition to JAXB one :
http://weblogs.java.net/blog/mhadley/archive/2006/03/index.html) then it'd really make REST an easy step, IMHO. This is where stubs
would be good in that that they could serve as a first step : they do all the 'difficult' job and more importantly make it easy to
'navigate' through XML
It'd be then up to a developer to get rid of stubs if he/she gets convinced in
the benefits of using REST....
Cheers, Sergey
On Sep 7, 2006, at 10:43 PM, Oisin Hurley wrote:
A few comments. First, "few verbs" is not a key idea of REST.
It is a very strong guideline IMO :)
Not to be overly pedantic, but Fielding [1] never mentions anything
about interface size in his thesis. Rather, he stresses the uniform
interface constraint and interface generality, which as I said in my
original email naturally results in "interface smallness" as a by-
product.
Second, putting the verb in the URL is a Really Bad Idea™.
I would go further down the path and say - this really isn't
allowed at all.
I fully agree, but saying it that way wouldn't have allowed me to
include the cool trademark sign in my message. ;-)
More comments below.
There's much more I could say about what you've written in the wiki, but let me cut it short and simply ask this: what are the
goals of having CXF "support REST"? Who or what does it benefit? What kinds of systems do you envision making use of that
support? Considering these questions and their possible answers within the constraints of the REST architectural style [1] is
the only way to get this truly right, IMO.
I can only talk for the use case that I have direct access
to - I have a server that maintains a memory model of a
set of entities that can be serialized to an XML vocabulary.
These set of entities can be influenced by a client
application, local to the client's address space. The
set of entities may be large, so the client loads entities
on-demand. If changes are made on the client side, the
changes are collated using an XML change language and
are submitted to the server - the server applies the
changes to the definitive set of entities that it maintains.
So - the set of entities is reflected as a Resource, with
a URL (in fact the entities themselves are also resources,
so to load a resource, the client issues a GET).
When the client issues the change request, it is couched
as a POST accompanied by the change language document.
The implementation on the server side receives a 'post'
method call with an XML document as the argument - there
is no type mapping, unmarshalling or any of that, it is
pretty much an application protocol approach. The content
of the POST expresses an update to the state of the
resource.
Summary: cxf supporting REST means that there is a
way to program servants to react to HTTP as an application
protocol, rather than as a layered protocol.
What you say about using HTTP as an app protocol -- as it was
designed to be used, frankly -- is definitely a requirement. However,
there's more as well -- REST also requires supporting navigation of
application state via hyperlinks, which means that CXF has to enable
and perhaps help the server-side application to generate the URLs
required to identify new resources that it creates and tie servants/
implementations to them. Applications have to play their part, too,
by following the semantics of HTTP, such as ensuring that GETs are
idempotent, and ensuring that the URLs it produces for its resources
and state aren't just always temporary or transient.
The web is actually a big distributed object system [2]. As such,
much can be learned about how to implement the dispatching part of a
REST system by looking at how systems like CORBA ORBs implement
dispatching.
--steve
[1] <http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm>
[2] <http://www.w3.org/People/Connolly/9703-web-apps-essay.html>=
