8 Nov
2012
8 Nov
'12
3:28 p.m.
On 11/08/2012 02:45 AM, Vincent Massol wrote:> Hi Caleb,
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).
This sounds like a major problem for "just use servlet3" answer unless we were
to offer a generic initXWiki() function which everybody's servlets could call. My
proposal is to write our own servlet which redirects to the user's servlet and it can
do the necessary initialization (although I hope we can minimize that initialization to
improve performance).
On Nov 7, 2012, at 2:41 PM, Caleb James DeLisle <calebdelisle(a)lavabit.com> wrote:
There is the expense of porting REST, GWT and WebDav servlets and maintaining those ports,
also if we want to use WebSocket, JsonP or other comet solutions (which I think could give
us a big performance boost) we need to port those libraries too and since they have to do
some clever things with the servlet, we might find that they use features which are simply
unavailable in our abstraction layer. Why make all of the work?
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
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?
Take the realtime editor, right now it uses the GWT RPC by loading a module which
implements the GWT service and it picked up by the GWT servlet. I want it to use websocket
if available or fall back on flashsocket, jsonp, or long polling. There is a library to do
this called Atmosphere, it uses a servlet and detects what the container and browser
supports and uses what it can. I want to include this but I want it to be an extension
because everything should be an extension for the sake of
modularity.
2/ Do we really want to support adding/removing
servlets at runtime?
"Everything should be an extension" and "extensions can be loaded at
runtime" make it a yes.
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.
There are a number of URL parts which redirect to the "bin" servlet and there
are also some other funny URL matchers, I think the best thing to do in this case is to
use either web.xml hackery or a request filter which is explicitly pulled in from web.xml
but comment it and say it is deprecated and nobody should be doing this.
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.
I suppose there's nothing really stopping us from using a pluggable URL handler once
the request enters the "ServletRedirectorServlet" as I propose, I don't
think it's a very good idea because I suspect that changing the URL scheme would cause
weird issues all throughout the code and which would take time to resolve and while
it's kind of nice to be able to arbitrarily change the URL scheme, it doesn't
bring the user any major features.
Thanks
Caleb
Thanks
-Vincent
WDYT?
Are there reasons not to do this which I missed?
Caleb
_______________________________________________
devs mailing list
devs(a)xwiki.org
http://lists.xwiki.org/mailman/listinfo/devs