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

Lincoln Baxter, III lincolnbaxter at gmail.com
Fri Feb 22 00:28:15 EST 2013


Wait, JavaCore is or is not related to JDT?


On Thu, Feb 21, 2013 at 7:18 PM, John Franey <jjfraney at gmail.com> wrote:

> Apache bcel hasn't had a release since 2006.  I'm wondering if the class
> file format has moved on beyond bcel's reach.  Its last official release is
> 5.2 in Feb 2006. Java 1.6 was released in December 2006, and nothing new
> from bcel project.  Java 1.7 in 2011, and still silence.  I wonder if it
> can support later class file formats somehow.
>
> javassist's latest release is December 2012 and seems to have jboss
> backing.  Seems a safe choice on the face of it.
>
> Then, there is eclipse JavaCore.  I wonder if JavaCore can be used without
> an eclipse workbench.  If so, JavaCore can provide a single api for both
> source and binary classes, so it could replace the forge java source
> parser, too.  I also wonder if forge could be a headless eclipse
> application - imagine the eclipse plugins available via forge's command
> line shell.
>
>
>
> On Thu, Feb 21, 2013 at 6:30 PM, Lincoln Baxter, III <
> lincolnbaxter at gmail.com> wrote:
>
>> 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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>>>>>>>>>
>>>>>>>>>
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>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>  --
>>>>>>>> Lincoln Baxter, III
>>>>>>>> http://ocpsoft.org
>>>>>>>> "Simpler is better."
>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> forge-dev mailing list
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>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Lincoln Baxter, III
>>>>>> http://ocpsoft.org
>>>>>> "Simpler is better."
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Lincoln Baxter, III
>>>>> http://ocpsoft.org
>>>>> "Simpler is better."
>>>>>
>>>>> _______________________________________________
>>>>> forge-dev mailing list
>>>>> forge-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/forge-dev
>>>>>
>>>>
>>>>
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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."
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