8 Nov
2012
8 Nov
'12
3:49 p.m.
On Nov 8, 2012, at 3:28 PM, Caleb James DeLisle <calebdelisle(a)lavabit.com> wrote:
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).
I assume that by "redirect" you don't mean a servlet redirect but you mean
doing a new MyServlet() and simulating a call to service()?
Indeed if possible it would be nice.
As much as possible indeed.
There are 2 aspects:
- letting the user control his URLs. this is a much requested feature. This is what is
currently implemented in the url module.
- handling cases when we don't control the URL because it's controlled by some 3rd
party framework for example or simply because webdav doesn't have the same url scheme
as xwiki's REST API for ex. So we need to have one url scheme per "servlet".
This is not currently supported by the URL module AFAIR.
Now there might be some gotchas. For example a lot of servlets require to be configured
through parameters in web.xml so this means we would still need to be able to edit web.xml
and thus not support proper extensions. We could of course define those on the main
servlet with some specific key syntax but it doesn't remove the need to declare them.
Actually, we can probably simulate this too by taking the configuration by using our own
Configuration module and bridging with the Servlet api… We would need to be able to
simulate ServletContext.getInitParameter() for example. I guess we can do this with a
WrappingServletContext :)
In any case since OSGi is doing this I guess it's doable. I hope there are no real
gotchas…
I'm warming up more and more on this proposal Caleb :)
Thanks
-Vincent
On 11/08/2012 02:45 AM, Vincent Massol wrote:> Hi Caleb,
Yes, obviously, this solution works best when the underlying frameworks are meant to be
embeddable as otherwise there's too much code to write/maintain.
Note that using Servlets means we cannot use component injection and we have to use the,
currently deprecated and static Utils.getComponent() APIs.
If we go this way we should definitely provide a generic AbstractXWikiServlet which does
initialization and allow getting the component manager.
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