How about CGLib instead of ASM directly? ASM is a bit complex and
necessitates a certain knowledge of the JVM op codes. IMHO, CGLib seems
high level enough to make this work. Thoughts?
Jeff
Bill Dudney wrote:
> Hi Andrus,
>
> Sorry for such a tardy reply but I'm just getting going on the JPA stuff...
>
> Jeff and I were at TSS Symposium last week and we had a chance to talk
> through the work for JPA. I wanted to get our thoughts into an email and
> off to the list so we are not duplicating work. We are planning on doing
> the mapping work. Jeff is going to tackle handling the annotations and I
> am going to handle parsing the orm.xml files and augmenting the mapping
> info.
>
> Other thoughts etc are inline.
>
> On Mar 7, 2006, at 2:45 AM, Andrus Adamchik wrote:
>
>> I did a little research on bytecode enhancement (CAY-460) and wanted
>> to share some thoughts.
>>
>> It turned out that it is fairly simple to modify bytecode with the ASM
>> framework:
>>
>> http://asm.objectweb.org/
>>
>> I checked in a basic enhancer that adds objectId and persistenceState
>> properties to POJOs already. Coding the rest of the DataObject
>> enhancements shouldn't be a problem, however ASM code is not something
>> that is easy to maintain by hand (so if say CayenneDataObject changes
>> internally, I'd like the enhancer to pick up such changes
>> automatically). I guess we may implement some sort of template based
>> approach. ASM allows to take an existing class X and generate regular
>> Java code that can act as a script for creating class X bytcode from
>> scratch. So theoretically an enhancer itself can be generated.
>>
>
> This looks interesting. I like the idea of using ASM to weave in the
> required enhancements. I looked at the code you checked in and I'm happy
> to start down the path of getting the rest of the required code woven
> in. I will also start looking at the template based approach. I will
> probably do this before I get to the XML work so we can start testing ASAP.
>
>> BTW, ASM visitor API can be used for another purpose - processing
>> annotations (CAY-456), thus solving two problems at once.
>>
>
> This looks cool (the ASM is really cool for doing this kind of work
> AFAICT). Jeff is going to head down this path.
>
>>
>> Another issue is integrating the enhancer in the provider. The
>> requirement is that enhanced classes must be accessible to the
>> application ClassLoader, so my original solution with a specialized
>> child ClassLoader won't work. I see three ways to do the integration
>> (we may implement all three of them).
>>
>> 1. "cgen" - by merging all CayenneDataObject code in the class
>> generator template. This will work for people who use Cayenne to model
>> their ORM classes, but want a superclass that is not a DataObject.
>> This is not suitable for persistent classes created outside Cayenne
>> and deployed with Cayenne provider.
>>
>> 2. "cdeploy" - enhancing compiler Ant task ala JDO.
>>
>> 3. Runtime - this would use JDK 1.5 java.lang.instrument API. On the
>> one hand it is the least intrusive option, but on the other it
>> requires a special runtime parameter (-javaagent:cayenne.jar).
>>
>> Ideas, comments?
>>
>
> From my reading of the spec it looks like the ClassTransformer is there
> so that 3 does not require the special runtime parameter. Is there
> something that I'm missing? I am basing my assumptions on the comment
> (starting on page 148) on the addTransformer(ClassTransformer) method on
> the PersistenceUnitInfo class.
>
> Thoughts welcome. Also if you are doing any of this work please speak up
> so we don't duplicate.
>
> TTFN,
>
> Bill Dudney
> MyFaces - http://myfaces.apache.org
> Cayenne - http://incubator.apache.org/projects/cayenne.html
>
>
>
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