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Re: [aspectj-users] EMF and AOP (spring like?) 
Hi Andrew,

maybe my question is more for the aspectj-dev list: I want to
implement a new type of advice that does not act at the level
of java interfaces. Instead I'd like to add it to the objects
created and defined by EMF. This is probably similar to
adding aspects to a scripting language embedded in java.

I know how to add advice to the eGet/eSet methods. But I want
to use the aspectj pointcut syntax to access methods that are
dynamically called. The methods may exist as java methods. They
are only available reflectively by the eGet/eSet methods...

Michael


Hi Michael,

If I understand you correctly, you would like to use AspectJ on an
EMF-generated library.  You would like to advise the eGet and eSet
methods on the generated classes that are accessed using reflection.
If this is what you are looking to do, then there shouldn't be any
problem using AspectJ.

Write your advice to advise the execution of the desired eGet and eSet
methods.  Place the  generated EMF code on the inpath of your aspect
library.  This will perform binary weaving of the EMF code.

I am not exactly sure how EMF works in reflective mode, but perhaps
your advice will look something like:

Object around(EStructuralFeature feature) :
EObjectImpl.eGet(EStructuralFeature) && args(feature) : {  ... }

--a

On Fri, Oct 3, 2008 at 7:18 PM, Michael Scharf <Michael-Scharf@xxxxxx> wrote:

Hi,

currently, I am adding what some AOP like features
too my EMF (http://www.eclipse.org/modeling/emf/)
application. I realized I am reinventing aspectJ
and I wonder if I can use aspectJ.

A simplified view of EMF: a ECore model defines objects with
attributes:

 class Person {
    attr String name;
 }

EMF can run in two modes: generated code and reflective.
In case of code generation the following code would be
generated for the above ecore model:

 public class Person {
    protected String name;
    public String getName() {
       return name;
    }
    public setName(String newName) {
       name=newName;
   // some code to notify listeners
    }

 }

Here one could use normal aspectJ. What interests me more is
the reflective case. In the case of reflective EMF instance
would have to be used like this (simplified version):

  name=person.eGet("name"); // in reality the attribute name is not string
  person.eSet("name", "Michael");

Essentially, any access of EMF objects funneled through the eGet/eSet
methods.

I want to define some advices for some of the getters and setters.
E.g. an advice for supplying some calculated default value on the
getter:

@Aspect
public class DefaultExample {

 @Around("com.xyz.myapp.Person.getName()")
 public Object addDefault(ProceedingJoinPoint jp) throws Throwable {
    EObject target=(EObject)jp.getTarget();
    // I somehow need to get to the structurel feature representing
    // the "name" attribute
    EStructuralFeature attribute=EMFAspectJHelper.getAttribute(jp)
    if(!target.eIsSet(attribute)
       return "My calculated default Value";
    return jp.proceed();
 }
}

I have found the docu for spring AOP
 http://static.springframework.org/spring/docs/2.5.x/reference/aop.html
I have never used spring but it seems they use some aspectJ library
to implement AOP for spring.

So, here is my question: Is it possible to use AOP in way that I
could add aspects to some reflective API like EMF? I mean is there
some calls I could make in the eGet/eSet methods to weave in aspects?

Here is how envision how this could work: Suppose I create a subclass
of EObjectImpl (the class that defines eGet/eSet). All eSet/eGet
would be handeled by my class. This class would then be used
for all dynamic access eGet/eSet:

// a class that adds AOP to dynamic EMF
class AopEObjectImpl extends EObjectImpl {
   // the magic from aspectJ
   MagicAspectJ aspectj;
   @Override
   public Object eGet(EStructuralFeature feature) {
       // let aspecJ doo the call for me. In case
       // the original method is needed
       // (JointPoint.proceed()), call eOriginalGet.
       return aspectj.call(buildGetSignature(feature));
   }
   // this calls the original get method
   public Object eOriginalGet(EStructuralFeature feature) {
       return super.eGet(feature);
   }
   private Signature buildGetSignature(EStructuralFeature feature) {
       // somehow create the signature like "com.xyz.myapp.Person.getName()"
       return signature;
   }
}

The MagicAspectJ would then do the magic for me of looking for
aspects and call the aspects that I have registered with
MagicAspectJ...

Am I dreaming here? Does aspectJ provide a way of using
aspects for dynamically called methods?
Any docu or example I can start with?

Michael

--
Michael Scharf
Wind River Systems GmbH
http://www.WindRiver.com
http://MichaelScharf.blogspot.com/

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aspectj-users mailing list
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--
Michael Scharf
Wind River Systems GmbH
http://www.WindRiver.com
http://MichaelScharf.blogspot.com/

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