[Jersey] Re: Migrating RPC to REST

From: Markus Karg <>
Date: Thu, 7 Apr 2011 20:57:15 +0200

Now we come right to the point: Is an application RESTful if it does not
transfer STATE but just transfers a COMMAND (i. e. a remote procedure call
-- RPC)? Most RESTafarians would say: No, because the COMMAND must be the
VERB (not the address or the payload), and there *must* be a transferred
STATE (i. e. in this case: an unwanted payload).


Most applications declared to be RESTful (possibly solely due to the fact
that they are built ontop of JAX-RS) already omit REST's key principle
HATEOS, and we still call them RESTful (are we allowed to do that?). If we
now go on and remove STATE transfer (the ST in REST), what is left over from
REST? What we then have is an RPC type service using http directly instead
of SOAP ("SOAP free http based RPC").


So, does that mean that actually there is no real world application that is
actually RESTful? Do we all cheat? Do we actually *want* REST, or do we just
want "SOAP free http based RPC plus simplified CRUD support" in JAX-RS? I
asked that because I am a JAX-RS 2 EG member an like to know what Jersey
users actually do. As it seems, they do not do REST, so maybe JAX-RS should
become "Servlet++" instead of REST?


I explicitly ask this question to the Jersey users because I want to know
what Jersey users are doing with Jersey and why they think what they are
doing is RESTful or couldn't be done with "Servlet++" instead of JAX-RS. The
purely philosophical question (how much REST must there be in REST) is
clearly defined and to was discussed already at rest-discuss (no HATEOAS no
STATE ? no REST !).


What is your opinion?


From: Jason Erickson []
Sent: Donnerstag, 7. April 2011 00:59
Subject: [Jersey] Re: Migrating RPC to REST


I would improve this slightly by posting to /my-orders rather than
my-shopping-list/new-order, but in my opinion, that doesn't make the example
given *not* RESTful, but I think this conversation might benefit from a
definition of RESTful. A RESTful web service *usually* is essentially a set
of CRUD verbs on a "resource" - the "R" in REST, but according to Wikipedia
<> , to be
RESTful, one needs to comply with a set of constraints that don't really
require a "resource" in all cases. There are also a set of "Guiding
Principals" that seem to require resources to exist in the system, but I
wouldn't read it as requiring a resource for every single request, so long
as the constraints are still respected.


And if you disallow "commands", which was my abstract version of the more
concrete example of an order, are we saying that POST can only create a
resource and if it has side-effects (e.g. it starts an order-fulfillment
workflow process, or kicks off a stored procedure) then it's no longer a
RESTful architecture? In that case, RESTful architectures become quite
limited as basically resource repositories. I take REST to be much more
flexible than that.


I realize that Wikipedia is not the canonical source, but I don't know what
Markus means when he says something is not RESTful.


On Apr 6, 2011, at 3:32 PM, Conal Tuohy wrote:

Markus, I think there probably are RESTful solutions to your problem, and I
understand you are interested in the general case rather than your
particular case (with the stored procedure), but others have already pointed
out that you would need to be more specific about the problem (i.e. the
domain itself) to elicit those solutions, because, in short, any RESTful
solution will need to represent your domain model. So long as the problem is
posed in the abstract, or in terms of "running a stored procedure" (which is
too low-level) then the business domain remains obscure, yet the domain is
the key to formulating a concrete solution.

So I will make up an example:

A supermarket shopper has a shopping list which they can save and reuse. I
have one of these with my local supermarket, Coles. Every few weeks I can go
on to the Coles website, maybe tweak the list a little, adding an item,
removing an item, and then click "Buy Now" which I imagine transfers my
shopping list to another list (a "packing list") which someone at the Coles
warehouse uses to pack up some cardboard boxes for me.

Is there a RESTful solution to this which doesn't require my browser to
download my entire list and re-upload it?

I think there is. I don't need to upload the list, because it is ALREADY
there on the server. If my shopping list was linked to an associated
resource (an "ordering service") which I could POST to to say "Create a
order (from this list) and get packing!", then that would IMHO be perfectly

e.g. imagine my shopping list had a representation like so:

GET /my-shopping-list/

<shopping create-order="new-order">

Then I could POST

POST /my-shopping-list/new-order

... and it would create an order from my list, returning me a redirect to:

GET /my-orders/order-3

<order date="2011-04-07" number="3">

On 06/04/11 21:30, Markus Karg wrote:



the intention of the question is a theoretical interest in REST idioms used
by Jersey users. There is no technical problem which I would be unable to
solve on my own, I just wanted to get an overview of the idioms and patterns
used by Jersey users to solve problems like these. So the discussion is not:
"Why to do REST?" as doing REST is the given constant in this paradigma.


I want to find out whether there is a common sense (pattern or idiom) among
the Jersey users for solving any member of this class of problems ("copying
data inside of the server without GETting it first and PUTting it later").
The problem is common and not tied to one particular, actual business domain
use case.


As Jan correctly pointed out, without any transfer, it wouldn't be RESTful
by definition. So the end of the discussion is reached obviously: There
cannot exist a valid solution, since REST *must* forward the
representational state (a command, in any form, is not a representational


To sum up:


In WebDAV, COPY is the best technical approach, but it is not RESTful.


In pure HTTP, PUT with some kind of additional source URL would be the best
technical approach, but it is not RESTful.


To be RESTful, the source object *must* get transferred by definition, so in
this class of problems, it must get copied twice. With REST applied to http
this means, GET and PUT of an unchanged object. A technical help for
performance is using a caching proxy most near to the client to at least
prevent a GET content transfer over the whole web. AFAIK a PUT cannot be
optimized in that way as it must not store into a cache (maybe I am wrong
with that).


So now I know what I wanted to know: There cannot be a RESTful solution. If
it must be RESTful, then it *must* copy the source twice over the LAN.


Thanks to all participiants. :-)





-----Original Message-----

From: Marek Potociar []

Sent: Mittwoch, 6. April 2011 12:03


Cc: Markus Karg; 'Arthur Yeo'

Subject: [Jersey] Re: Migrating RPC to REST


Hi Markus,


Have you considered to actually NOT replacing this stored procedure call
with RESTful architecture? Perhaps I am missing

some important piece of information from your use case, yet from what was
discussed here it seems to me that in this

case RCP-style call may be actually more suitable for your use case.


What features of the RESTful architecture do you want to leverage in this
use case (scalability, cacheability, loose

coupling, transparency ...)? IOW, why do you want to expose the stored
procedure in a RESTful way?




P.S. I agree with what Jan wrote earlier - if you really need to redesign
this use case in a RESTful way, you need to

look at the operation as a (temporal) service resource in the context of
it's domain. Then you might be able to properly

define the resource including the URI scheme, HTTP operations and payloads
etc. It is however difficult to make concrete

proposal based on the "INSERT FROM SELECT" information :)


On 04/05/2011 10:46 PM, Markus Karg wrote:

You're right, but that doesn't solve the problem that your proposal is not
RESTful: A PUT must provide the source entity

as a body. How will you provide the URL of the source without breaking the
rules of RESTfulness? See, the question was

not "How to call a stored procedure using http?" but "How to call a stored
procedure in a RESTful way?".










*From:*Arthur Yeo []

*Sent:* Dienstag, 5. April 2011 20:00


*Cc:* Markus Karg

*Subject:* Re: [Jersey] Re: Migrating RPC to REST




If the URL species the PK of the INSERT, which I take it to mean the unique
ID for the new rsrc, then you should be

using a PUT instead of a POST.


On Tue, Apr 5, 2011 at 10:52 AM, Markus
Karg<<>> wrote:






there is one thing you are missing: How to tell POST where to take the data
from (i. e. the PK used in the WHERE clause

of the SELECT)? Obviously you need to pass it as some kind of header with
the POST (the URL of the POST is the PK of the

INSERT, not the PK of the SELECT). So it is not RESTful, as Jan pointed out
this afternoon already.










*From:*Arthur Yeo [<>]


*Sent:* Dienstag, 5. April 2011 19:24

*To:* Markus Karg





*Subject:* Re: [Jersey] Re: Migrating RPC to REST




If the data is self-generated within the sproc from a SELECT and the sproc
is using that data to do an INSERT, I do not

see a reason to put anything in the POST, not unless you have some params.




You are creating a new resource with your POST which is carried out by your
original sproc. There is no payload in the

POST for this case.


Your POST, in this case, is even lighter weight than ordinary POST that has
a payload.


You did not change the meaning of a POST. Just make sure you return some
kind of identification back to the frontend for

the creation of that new rsrc.




On Tue, Apr 5, 2011 at 10:11 AM, Markus
Karg<<>> wrote:






if you want to do a POST, what actually do you like to send as the body? As
Jan correctly pointed out, sending an empty

body is not RESTful.










*From:*Arthur Yeo [<>]

*Sent:* Dienstag, 5. April 2011 18:59


*Cc:* Markus Karg

*Subject:* Re: [Jersey] Re: Migrating RPC to REST




Then, I am not understanding your concerns.


If there's already an sproc to do an INSERT based on some SELECT, all you
have to do is to either do a POST/PUT over

JDBC to call that sproc, depending on your application's needs.


I do not see how the data is is moved twice? Please elaborate.




On Tue, Apr 5, 2011 at 9:45 AM, Markus
Karg<<>> wrote:


I never said that I want to break up the INSERT FROM SELECT. In fact I still

want to call the stored procedure. But I want to discuss a possibly RESTful

interface for calling a stored procedure.


-----Original Message-----

From: Arthur Yeo [<>]

Sent: Dienstag, 5. April 2011 16:50


Subject: [Jersey] Re: Migrating RPC to REST


Is there a reason why you have to break up the INSERT and SELECT? I

thot u said these are all handled in a sproc?




On Tuesday, April 5, 2011, Markus
Karg<<>> wrote:

Hello Jersey Community, we're in the process of migrating some

functionality from RPC to REST and stuck with an issue we'd like to

discuss with you. :-) One of the business procedures we're migrating

was implemented as a stored procedure. It actually did nothing special

but just provided a copy of a rather big amount of records in a single

transaction. You can think of it in terms of SQL as "INSERT FROM

SELECT". In JAX-WS's RPC style it was just wrapped with a method of a

@WebService that called the stored procedure. But how to convert this

to a RESTful style in JAX-RS? Our initial idea was to do a http GET to

load the source, then forward that same XML body to a http POST.

Obviously that is RESTful and simple to do, but it means moving a

really, really big bunch of information twice over the web, just for

the sake of RESTfulness (and it would be two transactions, obviously).

Has anybody an idea how to RESTfully model this use case, so that the

data is not transferred at all but we still can just call the existing

stored procedure? The only idea we had would be doing RPC style, like

http post with a Location-header pointing to the source. But obviously

that is not very RESTful. Any ideas? :-) RegardsMarkus


Arthur Y.
Arthur Y.
Arthur Y.
Arthur Y.
Conal Tuohy
eResearch Business Analyst
Victorian eResearch Strategic Initiative