[forge-dev] reflection to access classes in project dependencies
Thomas Frühbeck
fruehbeck at aon.at
Thu Feb 14 12:05:00 EST 2013
Hmm, I expect loading of JARs not to the problem, is it? So the loading
and reflecting on the "external" class should be possible.
I was thinking of the next step, implementing kind of writable JavaClass
not just ignoring the changes, but making the modified class available
to the project.
Sorry if I misunderstood your quest? =)
Thomas
Am 14.02.2013 17:37, schrieb John Franey:
> Thomas,
>
> I have minimal exposure to proxy due to experience with hibernate, but
> my understanding is not adequate to understand how they would apply.
> Do I understand correctly that the benefit of a dynamic proxy is high
> when a temporary class implementation is needed, and when a method of
> the proxy is invoked, some action is taken, perhaps instantiating
> another implementation of the interface. In this use case, we don't
> need to invoke the methods of a project's class, we need to inspect
> the methods (and other members) of the class, right?
>
> John
>
>
>
>
> On Thu, Feb 14, 2013 at 11:22 AM, Thomas Frühbeck <fruehbeck at aon.at
> <mailto:fruehbeck at aon.at>> wrote:
>
> exactly what I was looking for :-))
> Thanks George!
>
> Am 14.02.2013 16:55, schrieb George Gastaldi:
>> Hi Thomas,
>>
>> Have a look in Forge 2.0 source code. We're using javassist at
>> it's best in the proxy module
>>
>>
>>
>> Em 14/02/2013, às 13:53, Thomas Frühbeck <fruehbeck at aon.at
>> <mailto:fruehbeck at aon.at>> escreveu:
>>
>>> Hi John,
>>>
>>> my two cents:
>>> - this feature is a must-have, if Forge should be more than
>>> a tool to iniitialize projects, really great idea
>>> - being pragmatic I would say this calls for proxy classes,
>>> similar to CDI decorators or the copy-on-write strategy
>>>
>>> (AFAIK the downside to CDI decorators is that they need
>>> interfaces on the base classes, thus again requiring changes of
>>> the classes if they hadnt been designed for it firstplace.)
>>>
>>> I have a very similar problem I am currently trying to solve
>>> with silly wrapper classes and was starting to think about
>>> dynamic proxy generation - unfortunately I have _no_ experience
>>> with such technology other than being simple user :-/
>>>
>>> Have you thought about javassist? Is it an option at all?
>>>
>>> Thomas
>>>
>>>
>>> Am 14.02.2013 16:21, schrieb John Franey:
>>>> My motivation for this email is to satisfy FORGE-773. However,
>>>> this is also related to FORGE-563 and FORGE-424, and resolution
>>>> could enable other features.
>>>>
>>>> I have written a prototype:
>>>> 1) an implementation of the forge java api interfaces which
>>>> delegates to java's reflection, offering a read only
>>>> perspective of java components.
>>>> 2) a forge module, currently a facet, to search for a given
>>>> binary class in the project's dependencies and returns the
>>>> result wrapped in the above delegate.
>>>>
>>>> These are demonstrable in a unit test.
>>>>
>>>> My dilemma now is how to integrate these into the forge
>>>> project. There are a few different areas, but I'll start with
>>>> this:
>>>>
>>>>
>>>> For some callers, a java class is a java class, whether it
>>>> originates as source code (from the current forge project) or
>>>> is a class from the dependency set. For example, scaffolding
>>>> primarily is a read only operation. In this use case, it would
>>>> be simpler for these clients to have a single interface to
>>>> resolve classes because whether a class is source or binary is
>>>> not relevant to the use case.
>>>>
>>>> On the other hand, there is a set of classes in a user's
>>>> project that are modifiable. In these cases, a java class is
>>>> not a java class. Forge components might want the distinction
>>>> somehow. There ought the be some distinction of which class is
>>>> modifiable and which is not.
>>>>
>>>> Naively, I took the first thinking that the existing forge java
>>>> model would be adequate. To have separate java api for
>>>> read-only and read-write java model objects seems a fundamental
>>>> addition to the java model which requires much more effort. In
>>>> absence of such a model, I though to implement 'no-op' for
>>>> those code changing methods (e.g., Named.setName() would be
>>>> inert). I assumed that forge component that change source code
>>>> would have necessary context to know when it is operating on a
>>>> source code module, avoiding attempts to modify a binary class.
>>>>
>>>> So, I'm looking for discussion and consensus on the above. Any
>>>> thoughts?
>>>>
>>>> Regards,
>>>> John
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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