Re: JSR311: Aggregation(?) of "Targets for _at_*Param, _at_DefaultValue, @Encoded"

From: Stephan Koops <>
Date: Sat, 22 Mar 2008 13:30:40 +0100

Hi Marc,
>> aggregation of discussion for root resource classes
>> if I collect the disussion points of the last days, I think we can
>> aggregate this to the following points realting to @*Param:
>> Allow @*Param on parameters, fields and setters (setters are
>> not required to be thread save)
>> singelton lifecycle runtime environments must reject root
>> resource classes (rrcs) with annotated fields or setters. (Other
>> possibilities with Numbers and CharSequences are to complicated)
>> This is close to (iv) of the proposals of Marc.
>> Paul, Marc, is this right? Did I forget something important?
> Not exactly my suggestion. I don't think an implementation should be
> required to police use of @*Param annotations on fields+methods of
> resource classes with lifecycles other than per-request. If an
> implementation defers object creation to an IoC framework it may not
> know the lifecycle so it can't be expected to enforce it. I suggest we
> warn developers about the consequences (i.e. it will probably break),
> offer an alternative (use resource method params) and then caveat emptor.
That's also good. IMO the singelton runtime should (or must?) check it
and reject the rrc if necessary.
>> BTW: What about other instance fields? They may cause trouble in
>> singelton lifecycle rrcs -> reject rrcs with any instance field?
>> But there are questions for
>> non-root resource classes:
>> While thinking about (if all agree with the point above):
>> Non-root resource classes have app developer managed lifecycles (see
>> spec). For them I propose (not discussed):
>> If the lifecycle is per-request (or the app developer otherwise
>> ensures that only one thread uses it the same time, e.g. pooling):
>> the app developer can use @*Param on parameters, fields and setters.
>> If the lifecycle is singelton: the app developer must only use
>> them on method parameters.
>> It is the responsibility of the app developer to use them right
>> here. It is good to put a related warning in the javadoc of all
>> @*Param, and also in the spec.
> An implementation doesn't inject on non-root resource classes, see
> section 5.2 "Injection Scope".
Oh, yes. You are right.
> One thing we could do here if this is desirable is to allow a
> sub-resource locator to return a Class rather than an instance, the
> runtime would then instantiate an instance and inject that.
IMO: In the most cases of non-root resource intances an initialization
with IDs (or something like that) from the path or something like this
is needed. It could be read from the path, but I prefer (for me) to have
no dependency from a resource class to it's ancestor resource class.
But if others want this, we can specify this.
>> Independent of the results for @*Param, there is the same question for
>> @Context
>> Must instances be thread save or not? Neither the specification nor
>> the javadoc defines anything.
>> In rrcs it depends exactly on the used lifecycle: if singelton,
>> than @Context annotated fields must be thread save, if not, than not.
>> non-root resource classes may be singeltons or not, independent
>> of the lifecycle of the rrcs (app developer responsibility, see above)
>> Here a definition is needed, if a non-root resource classses can
>> estimate a thread save implementation of UriBuilder, SecurityContext
>> and so on. BTW: This must kept in mind also for @Resource of JSR-250
>> (and perhaps others).
>> A possibility is to not require thread safety; singelton non-root
>> resource classes must not use them on fields and setters (the same as
>> for @*Param for singelton non-root resource classes, see above); the
>> app developer has the responsibility to ensure, that he use it
>> correct. This is consistent to the proposal above.
> For @Context the injected instance should be a thread-local proxy. I
> thought I had included this in the spec but apparently not - sorry
> about that.
ok, may happen :-) Good, that we talk about this.

Is it right, that this is a solution, all can live with?

A possibility to avoid the unwanted using for a singelton ready resource
class implementation could be, to offer @*Param twice: One set in
package (same as now) and one set in a new package (or
perhaps in The implementations is valid on
only on parameters (as now), the other implementations on parameters,
fields and perhaps setters. So an app developer can take a look in his
import section, check if only correct implementations of *Param are
imported and he can be sure that his implementation works also in
singelton runtimes.
On the other hand this solution could confuse developers. Because of
that there should be an explanaition in the javadoc of the annotations
in both packages for it. If this create too much confusion, lets throw
this proposal away.

best regards