[forge-dev] reflection to access classes in project dependencies

Lincoln Baxter, III lincolnbaxter at gmail.com
Thu Feb 21 18:30:37 EST 2013 

What about something like this?

https://issues.jboss.org/browse/FORGE-795
https://issues.jboss.org/browse/FORGE-796


On Wed, Feb 20, 2013 at 11:11 AM, Lincoln Baxter, III <
lincolnbaxter at gmail.com> wrote:

> Hmm... I'm not sure. I think it would probably still be slightly
> misleading to have mutable interfaces for immutable objects, without some
> kind of indicator. For instance, if someone were to pass the object beyond
> its "intended" scope.
>
>
> On Tue, Feb 19, 2013 at 7:41 PM, John Franey <jjfraney at gmail.com> wrote:
>
>> Thinking out loud, would isEditable still be needed if there were a
>> lookup that returned only editable java resources, and another query that
>> could return both binary and source resources?  Plugins that operate as
>> editors would use the former to find resources it knows it will edit, and
>> will use the latter in order to inspect other classes (to resolve super
>> class or throws declarations).  Plugins that operate as readers (like
>> scaffold plugins) would use only the latter.  Hmm...even with isEditable,
>> does it make sense to have these two kinds of methods?
>>
>>
>>
>>
>> On Mon, Feb 18, 2013 at 9:43 PM, Lincoln Baxter, III <
>> lincolnbaxter at gmail.com> wrote:
>>
>>> I don't like it because it's not really optimal, but... I don't really
>>> see a better way forward that doesn't break every API we have.
>>>
>>>
>>> On Mon, Feb 18, 2013 at 9:43 PM, Lincoln Baxter, III <
>>> lincolnbaxter at gmail.com> wrote:
>>>
>>>> Well, I actually meant refactor the entire JavaParser so that the types
>>>> are immutable by default, but modifiable when desired by doing an intanceof
>>>> and cast. This would, as John said, be a fairly invasive, with a fair
>>>> amount of downstream API impact, since all users of these APIs would now
>>>> need to reference these new types instead. It would mean refactoring all of
>>>> Forge.
>>>>
>>>> So from the perspective of Migration, it probably makes sense to do
>>>> something like add a method "isEditable()"
>>>>
>>>>
>>>> On Thu, Feb 14, 2013 at 2:19 PM, Thomas Frühbeck <fruehbeck at aon.at>wrote:
>>>>
>>>>>  If I understood Lincoln correctly, he meant adding an interface
>>>>> EditableJavaSource, so no change in the existing implementations necessary.
>>>>> So the boolean is substitutable by instanceof, your graceful error
>>>>> handling would be supported.
>>>>>
>>>>> Am 14.02.2013 20:10, schrieb John Franey:
>>>>>
>>>>> I would follow my object-oriented instinct to agree that a
>>>>> editable/non-editable parallel of the model would make sense.  After all,
>>>>> an editable java source is kind of a non-editable java source, and adds
>>>>> editing behavior.....
>>>>>
>>>>>  However, the parallel model seems to be a significant undertaking,
>>>>> and has a negative characteristic, in my opinion.   Lets say there exists a
>>>>> method to search for and return a JavaClass, editable or not.  In a use
>>>>> case where the JavaClass is to be modified, this method is inadequate. 1)
>>>>>  The caller would have to check if the result is instance of
>>>>> EditableJavaClass, then cast, or 2) an alternate query method would be
>>>>> provided to return only EditableJavaClass and since methods cannot be
>>>>> overridden by return type the alternate query method would have to be
>>>>> defined in a different interface.  Not taht either of these are difficult
>>>>> to overcome, but I think the parallel model would increase overall
>>>>> complexity a little and add to the level of effort, and the benefit gained
>>>>> is merely type protection against the runtime error of attempting to modify
>>>>> a non-editable java component.
>>>>>
>>>>>  To go against that impulse just a second, consider the option of a
>>>>> property on the base class, a boolean: editable.  This would avoid the
>>>>> parallel model, avoid casting and support polymorphic calls.   The runtime
>>>>> error of attempting to modify a non-editable component can be handled in a
>>>>> few different ways: 1) a runtime exception, 2) a quiet no-op.  Without the
>>>>> editable property, I would not use a runtime exception.  There would be no
>>>>> chance for the forge plugin programmer to avoid the error gracefully.  With
>>>>> the property, the error is the programmer's and a runtime exception could
>>>>> be appropriate.
>>>>>
>>>>>  Regards,
>>>>> John
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Feb 14, 2013 at 1:11 PM, Lincoln Baxter, III <
>>>>> lincolnbaxter at gmail.com> wrote:
>>>>>
>>>>>>  As I understood it, we need a way of explicitly noting when a
>>>>>> JavaSource instance is mutable or not. Perhaps splitting the API into a
>>>>>> JavaSource an EditableJavaSource parallel.
>>>>>>
>>>>>>  It was also my understanding that proxies were going to be used to
>>>>>> do lazy-classloading for any JARs brought in via this system. I'm not sure
>>>>>> we need to worry about this just yet. We can get it working then think
>>>>>> about performance implications.
>>>>>>
>>>>>>
>>>>>> On Thu, Feb 14, 2013 at 12:23 PM, John Franey <jjfraney at gmail.com>wrote:
>>>>>>
>>>>>>>  I have no intention of providing a way to modify the class
>>>>>>> definition of a java class defined within a dependency of the user's
>>>>>>> project.
>>>>>>>
>>>>>>>  Putting the question another way:
>>>>>>>
>>>>>>>  To date, the forge java model today supports only modifiable java
>>>>>>> components.  This effort introduces non-modifiable java components to the
>>>>>>> forge java model.   This raises the question:  Would the non-modifiable
>>>>>>> java components be inspected with the same api that supports the modifiable
>>>>>>> java components (JavaClass, and others).  If no, what api is used to
>>>>>>> inspect the non-modifiable java components?
>>>>>>>
>>>>>>>  My naive answer is: the non-modifiable java components would be
>>>>>>> inspected using the same api as the modifiable java components.  Methods of
>>>>>>> that api that expressly modify the java component would be inert for
>>>>>>> non-modifiable java components.
>>>>>>>
>>>>>>>  John
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Feb 14, 2013 at 12:05 PM, Thomas Frühbeck <fruehbeck at aon.at>wrote:
>>>>>>>
>>>>>>>>  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
>>>>>>>> > 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>
>>>>>>>>> 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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>>>>>>>>>
>>>>>>>>>
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>>>>>>>>>
>>>>>>>>>
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>>>>>>>>>
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>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>>>>
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>>>>>>
>>>>>>
>>>>>>
>>>>>>  --
>>>>>> Lincoln Baxter, III
>>>>>> http://ocpsoft.org
>>>>>> "Simpler is better."
>>>>>>
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>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Lincoln Baxter, III
>>>> http://ocpsoft.org
>>>> "Simpler is better."
>>>>
>>>
>>>
>>>
>>> --
>>> Lincoln Baxter, III
>>> http://ocpsoft.org
>>> "Simpler is better."
>>>
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>
>
>
> --
> Lincoln Baxter, III
> http://ocpsoft.org
> "Simpler is better."
>



-- 
Lincoln Baxter, III
http://ocpsoft.org
"Simpler is better."
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