[cdi-dev] Which version of HttpServletRequest is injected?
arjan tijms
arjan.tijms at gmail.com
Thu Sep 8 08:28:56 EDT 2016
Hi,
On Thu, Sep 8, 2016 at 2:14 PM, Martin Kouba <mkouba at redhat.com> wrote:
> The best solution might be to let the servlet container provide the beans
> for all the servlet artifacts (HttpServletRequest, HttpSession and
> ServletContext).
>
+100 for that.
Several issues were already created for that in the past, but to my
understanding it was misunderstood by some in the Servlet EG and
subsequently closed. See https://java.net/jira/browse/SERVLET_SPEC-116
Specifically this comment was a little problematic:
GW> More over,
GW> I'm concerned that by making CDI to servlet mapping a responsibility
GW> of the servlet container, then we are going to have to do a
GW> container to CDI adaptation for every CDI implementation out there.
I think this is missing the key insight that CDI extensions are portable
and that it's "just" providing a 1 class extension that adds 3 orso
build-in beans.
Kind regards,
Arjan Tijms
>
> But it's more complicated then it sounds. For example, HttpServletRequest
> attibutes might be used as backing storage of the request context. So that
> it cannot simply change...
>
> Anyway, I think this problem deserves some attention from both the CDI and
> the Servlet EG.
>
> Martin
>
> Dne 8.9.2016 v 13:31 arjan tijms napsal(a):
>
>> Hi,
>>
>> On Thu, Sep 8, 2016 at 1:09 PM, Romain Manni-Bucau
>> <rmannibucau at gmail.com <mailto:rmannibucau at gmail.com>> wrote:
>>
>> Hit that issue as well several times.
>>
>> It is more vicious than it looks like IMO cause CDI will *never* get
>> *the* right request for everybody, it is as simple as that. Any part
>> of the app can rely on the wrapper level N (of course N being
>> different for each mentionned parts of the app).
>>
>>
>> What I was thinking, but maybe I'm wrong, is that the application never
>> "just" wraps the request and uses it for itself. It always passes it to
>> the container, which then passes it on to the next Filter, Servlet, or
>> whatever. So at that point the container code has the opportunity to
>> store the request as being the "current" one.
>>
>> E.g. if you do:
>>
>> RequestDispatcher dispatcher = servletContext().getRequestDis
>> patcher(...);
>> dispatcher.forward(wrap(request), response);
>>
>> Then the RequestDispatcher, which is a container class, receives the
>> wrapped request and can make it available.
>>
>> The other way around, eventually every AuthModule, Filter or Servlet has
>> to be called by the container at some point. E.g. the "protected void
>> service(HttpServletRequest req, HttpServletResponse resp)" is called by
>> the container.
>>
>> So just before the container invokes the HttpServlet#service method, the
>> container can store the request, and CDI (via an SPI) can pick it up
>> from there.
>>
>> That way in every context you can always have the *current* request (the
>> request that's passed in to the last Servlet or Filter call on the stack).
>>
>> Kind regards,
>> Arjan Tijms
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Best CDI can do is to provide the request it has (already the case
>> and cost pretty much nothing) and enable the user to produces very
>> easily its own request from its filter (or equivalent) for its usage
>> IMO - which is IMO already doable but maybe there is another
>> shortcut we can introduce I didnt think about. If you look one step
>> further any web framework built on top of CDI does it and therefore
>> runs in a well known context.
>>
>>
>> Romain Manni-Bucau
>> @rmannibucau <https://twitter.com/rmannibucau> | Blog
>> <https://blog-rmannibucau.rhcloud.com> | Old Wordpress Blog
>> <http://rmannibucau.wordpress.com> | Github
>> <https://github.com/rmannibucau> | LinkedIn
>> <https://www.linkedin.com/in/rmannibucau> | Tomitriber
>> <http://www.tomitribe.com> | JavaEE Factory
>> <https://javaeefactory-rmannibucau.rhcloud.com>
>>
>> 2016-09-08 13:03 GMT+02:00 arjan tijms <arjan.tijms at gmail.com
>> <mailto:arjan.tijms at gmail.com>>:
>>
>> Hi,
>>
>> On Thu, Sep 8, 2016 at 12:40 PM, Martin Kouba <mkouba at redhat.com
>> <mailto:mkouba at redhat.com>> wrote:
>>
>> that's a good question. In Weld, the request object is
>> captured during request context activation, i.e. during
>> ServletRequestListener.requestInitialized() notification and
>> before any filter or servlet is invoked. So wrappers are
>> ignored and the original/first request is used.
>>
>>
>> Indeed, although do note that some servers (Liberty and WebLogic
>> I think) send the ServletRequestListener.requestInitialized()
>> notification rather late, and do that after the application
>> already has seen the request and has had a chance to wrap it.
>> This by itself is a separate problem. So on these servers, Weld
>> would receive an early request but not necessarily the earliest.
>>
>>
>> But TBH I don't think we can fix this easily as I'm not
>> aware of any portable way to listen for "wrapping actions".
>>
>>
>> This would have to happen with Server specific code I guess,
>> just as Weld now requires an SPI to obtain the current principal
>> for injection.
>>
>> You could say that the Servlet container could store the request
>> "somewhere" on a stack structure, just before it invokes the
>> ServerAuthModule, Filter, Servlet and anything else I may have
>> forgotten, and then when control flows back to each Servlet,
>> Filter, etc unwind that stack.
>>
>> At the very least the spec for now should perhaps clarify this?
>>
>> Kind regards,
>> Arjan Tijms
>>
>>
>>
>>
>>
>> Martin
>>
>> Dne 8.9.2016 v 11:02 arjan tijms napsal(a):
>>
>> Hi,
>>
>> The CDI spec defines a built-in bean for the type
>> HttpServletRequest. In
>> 3.8 it says:
>>
>> "A servlet container must provide the following built-in
>> beans, all of
>> which have qualifier @Default:
>>
>> a bean with bean type
>> javax.servlet.http.HttpServletRequest, allowing
>> injection of a reference to the HttpServletRequest"
>>
>> An HttpServletRequest however can be wrapped multiple
>> times and by
>> multiple artefacts. I.e. by a ServerAuthModule, Filter
>> and a
>> RequestDispatcher.
>>
>> The question now is; which version of the
>> HttpServletRequest is supposed
>> to be injected?
>>
>> * The first one in the chain?
>> * The last one in the chain?
>> * The current one at a given point in the chain?
>>
>> A little bit of experimenting seems to indicate it's now
>> often "one of
>> the first ones", e.g. the one that happened to be
>> current when e.g. a
>> ServletRequestListener that initialises a specific CDI
>> implementation is
>> called.
>>
>> I think this is a little confusing, as working with an
>> injected request
>> can now totally ignore the request wrapping that has
>> been done and break
>> an application badly.
>>
>> Thoughts?
>>
>> Kind regards,
>> Arjan Tijms
>>
>>
>>
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>>
>> --
>> Martin Kouba
>> Software Engineer
>> Red Hat, Czech Republic
>>
>>
>>
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