Hi Caleb,
On Nov 7, 2012, at 2:41 PM, Caleb James DeLisle <[email protected]>
wrote:
> Hi,
>
> I'd like to register servlets in the component manager and have them called
> by their hint.
> The oldcore struts servlet would be @Named("bin") and the rest servlet would
> be @Named("rest")
>
> Reasons to want to do this:
> * There are things which are currently impossible without a servlet, things
> like REST, GWT and WebDav.
REST and WebDAV for example can be done without needing a new Servlet by using
a tighter integration. I don't know enough about GWT to know if it's possible
or not but I guess it is too (at the expense or writing a bit more code since
you'll need to call some GWT APIs to do serialization/deserialization).
> * If somebody has servlet code and they want to make it run in XWiki, this is
> a real answer for them whereas "rewrite your app using XWiki actions" isn't.
Indeed, and we've been waiting for Servlet 3.0 so far. Last time we checked it
was still to early to use Servlet 3.0 (see threads on markmail).
> * Even if we had an Actions system which made it *possible* to implement
> REST, GWT, and WebDav entry points, we would have to rewrite the universe
> since all external libraries use Servlet.
> * Web.xml is an eyesore, it's full of content which is the concern only of a
> particular module, this could (mostly) be fixed by using injected servlets.
Indeed and Servlet 3.0 seems a good answer.
Now you're right that Servlet 3.0 doesn't support dynamic unregistration of
Servlets (only addition) so if we want to bring in servlets in an extension
that's not possible. This is also why I prefer the tight integration approach
which doesn't have this problem (i.e. do away with Servlets).
> The big reason not to like it is because it could undermine the proposal for
> Actions.
> The JIRA issue for actions http://jira.xwiki.org/browse/XWIKI-4713 was opened
> on January 1 of 2010.
> It is stalled because nobody really knows how to make an abstraction which
> represents Servlets or Portlets without any lost features.
I started the Action module and I didn't finish simply for lack of time.
There's no blocker. I wanted to finish the URL module before working on it
again but I didn't get the time to finish it either.
> If we make it easier for servlets to be used, we might begin down a slippery
> slope toward everything being done using servlets and then we lose portlet
> compatibility.
> But the alternative as I see it is to block progress in this direction and
> hope that somebody steps up to implement Actions which are fully compatible
> with portlets and servlets.
My take on Servlets within XWiki in general:
* We should not use Servlets when there are other ways of integrating external
tools. When possible a tighter integration should be chosen since it allows to
use our development practices with component injection and makes it simpler for
deployment (removes the burden to have to modify web.xml).
* Another reason for having only 1 entry point (or a minimal number of entry
points) is that defining more entry points is a pain for maintenance as we've
been experiencing over and over for the past years. The problem is that a new
entry point means that you need to duplicate all initialization of XWiki
Context/Execution context for each incoming request and this is tricky and all
our entry points were doing it wrongly at some point (case in point, Andreas
just fixed 2 bugs yesterday where some threads were not cloning the xwiki
context). Yes we should be able to factor all this init in a common place
(which we almost have but in practice it doesn't seem to really happen for some
reason).
Regarding your proposal:
* It seems a bit of hack to call a Servlet by doing a new on it. It goes
against the concept of Servlets actually which is supposed to be handled by the
Container. More generally what you propose is what OSGi is doing too:
- http://www.peterfriese.de/osgi-servlets-a-happy-marriage/
- http://felix.apache.org/site/apache-felix-http-service.html
The real questions for me are:
1/ Could you explain what's your actual use case so that we could discuss
alternatives, if any?
2/ Do we really want to support adding/removing servlets at runtime?
If the answer to 2/ is yes then your proposal is the only one I could see
working indeed.
Regarding @Named("bin"), I think it would be good to review all our existing
URLs and verify it'll work. For example ATM we also have "skin" and "skins"
AFAIR which are currently handled by the same Servlet as "bin" and thus we'd
need to find a solution for this too + we need to review the GWT, WebDAV URLs
too.
It would also be nice for the xwiki URL module to be able to handle different
URL formats based on the "servlet/service" instead of the scheme being fixed
for all which is currently the case.
Thanks
-Vincent
> WDYT?
> Are there reasons not to do this which I missed?
>
> Caleb
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