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Re: [aspectj-dev] Can I intercept before a class is load time weaved 
No, if you specify -XaddSerialVersionUID then AspectJ creates the SUID
based on the structure of the type prior to weaving.  Have you tried
it out?

public class A {
}
javac A.java
serialver A
A:    static final long serialVersionUID = -5362330504532103641L;

// introduce an aspect that would change it
aspect X {
  public int A.i;
}
ajc A.java X.java
serialver A
A:    static final long serialVersionUID = -7845631417099584748L; // changed

// ask aspectj to create the SUID
ajc -XaddSerialVersionUID -Xlint:warning A.java X.java
N:\temp\A.java [warning] calculated SerialVersionUID for type A to be
-5362330504532103641L
serialver A
A:    static final long serialVersionUID = -5362330504532103641L; //
returning field created by AspectJ

Andy

2009/9/18 Choudary Kothapalli <choudary.kothapalli@xxxxxxxxx>:
> Andy,
>
> Yes. But AspectJ does that after weaving the class. I do before
> weaving. After the class is weaved, fields may be added to a class,
> which generates a different SUID. The detailed problem description is
> in this thread:
> http://dev.eclipse.org/mhonarc/lists/aspectj-dev/msg02498.html
>
> Thanks,
> Choudary.
>
> On Wed, Sep 16, 2009 at 5:44 PM, Andy Clement <andrew.clement@xxxxxxxxx> wrote:
>>> To fix this, before passing the class to the weaver, I am checking if
>>> SUID is not defined in a Serializable class and if so, I am inserting
>>> one. That seems to solve my problem.
>>
>> Isn't that in fact a description of what the AspectJ
>> -XaddSerialVersionUID option does?
>>
>> Andy
>>
>> 2009/9/13 Choudary Kothapalli <choudary.kothapalli@xxxxxxxxx>:
>>> Hi Simone and Martin,
>>>
>>> Thanks for your pointers. I thought if I were going to write code at
>>> byte code and class loader level, I would rather solve my problem than
>>> implementing a work around. Here is what I did.
>>>
>>> Remember my original problem was because of a mismatch between SUIDs
>>> when AspectJ deserializes a class without SUID defined. The default
>>> Java generated SUID was not matching with the SUID of the AspectJ
>>> weaved class.
>>>
>>> To fix this, before passing the class to the weaver, I am checking if
>>> SUID is not defined in a Serializable class and if so, I am inserting
>>> one. That seems to solve my problem. I have changed
>>> org.aspectj.weaver.loadtime.Aj.preProcess(String className, byte[]
>>> bytes, ClassLoader loader) method for this and using my
>>> aspectjweaver.jar instead of the original jar.
>>>
>>> The source is at http://maintainj.com/temp/suidbug/Aj.java . There are
>>> some parts that I am not sure if I am doing right.
>>>
>>> a) It is about the temporary classloader I need so that I can load the
>>> class and use ObjectStreamClass.lookup(clazz).getSerialVersionUID() to
>>> find the SUID that Java would generate. For this I need to know the
>>> application classpath. I am assuming (and it is working in a client's
>>> Swing application) that the classloader instance passed to the
>>> Aj.preProcess(...) is URLClassLoader and I am calling getURLs() to get
>>> all the paths to search. I am passing null as the parent of my
>>> temporary classloader as the class should not be loaded before passing
>>> to the AspectJ weaver. Is this going to break in a J2EE environment?
>>> Is there a better way to find the classpaths to search? I couldn't
>>> find any temporary classloader implementation in your samples.
>>>
>>> b) Adding a field to a class in BCEL - While creating the
>>> ConstantValue for SUID of long type, I am passing 2 as its length and
>>> it is working. What does that length parameter really mean? The
>>> javadoc seems to say that it is the content length in bytes and as
>>> long is of 8 bytes, I gave 8 and it failed. I changed it 2 as that's
>>> what some snippet of AspectJ code was doing.
>>>
>>> Thanks again for your time and patience in addressing my problem
>>> though it really is not an AspectJ defect.
>>>
>>> Regards,
>>> Choudary Kothapalli.
>>> MaintainJ Inc.
>>>
>>>
>>> On Fri, Jul 31, 2009 at 11:36 AM, Simone Gianni<simoneg@xxxxxxxxxx> wrote:
>>>> Hi Choudary,
>>>> Martin is absolutely right, you need to :
>>>> - Implement your own classloader
>>>> - Use the weaving adaptor from there
>>>> - Decide which classes you want to pass to the adaptor and which you don't
>>>> want to
>>>> - To make this check, either use BCEL/ASM, or load the class in a temporary
>>>> classloader
>>>>
>>>> This last point is what you are asking for, to use reflection instead of
>>>> ASM/BCEL. You don't really have to, ASM/BCEL can quite easily check for the
>>>> presence of a static field in bytecode, and it's much much faster than using
>>>> reflection for this, but if you really want to, you can still load the class
>>>> in a temporary classloader (you can use an URLClassLoader), check it there
>>>> and the load it in your real classloader with or without passing it to the
>>>> weaving adaptor. The problem is that playing with classloaders this way is a
>>>> bit tricky;  not impossible or extremely difficult, just tricky, which means
>>>> you could spend hours trying to figure out why things are not working as you
>>>> expect before understanding what is really happening.
>>>>
>>>> If you want to, I have played a bit with AspectJ LTW classloading, you can
>>>> find some stuff here
>>>> http://svn.apache.org/repos/asf/labs/magma/trunk/maven-magma-plugin/src/main/java/org/apache/magma/tools/classloading/
>>>> . What you find there is a way to pipe a number of transformations (AspectJ
>>>> weaver -> OpenJPA enhancer -> Cobertura enhancer) and then load the
>>>> resulting class in the final classloader (in my case a webapp classloader).
>>>> It works in "pull mode", that is when the webapp classloader searches for a
>>>> class, it will search for a resource a/b/C.class to load the bytecode. When
>>>> this happen, the chain of transformers kick in, each pulling bytecode from
>>>> the previous one, so that the bytecode travels from the .jar file, via
>>>> aspectj, openjpa etc.. to the classloader requiring it.
>>>>
>>>> Some of these transformers (including AspectJ) uses temporary classloaders
>>>> in the middle. Maybe you can use that as a starting point and the add proper
>>>> "if" statements to bypass aspectj weaver for classes you don't need.
>>>>
>>>> The code that build the chain and uses it is found here
>>>> http://svn.apache.org/repos/asf/labs/magma/trunk/maven-magma-plugin/src/main/java/org/apache/magma/tools/maven/MagmaJettyRun.java
>>>> inside the execute() method.
>>>>
>>>> Hope this helps,
>>>> Simone
>>>>
>>>> Choudary Kothapalli wrote:
>>>>>
>>>>> This question follows the thread on InvalidClassException while
>>>>> deserializing classes without SUID. The link to that thread is
>>>>> http://dev.eclipse.org/mhonarc/lists/aspectj-dev/msg02496.html .
>>>>>
>>>>> I could not get rid of the exception and my only solution is to
>>>>> exclude all those Serializable classes without SUID. I ask my users to
>>>>> exclude those classes in aop.xml, but in a large legacy application,
>>>>> it is a tedious process. I need to find a simpler solution.
>>>>>
>>>>> A probable solution is to intercept just before weaving a class, check
>>>>> if that class is Serializable without SUID and if so, not to weave it.
>>>>> This would need two things:
>>>>>
>>>>> 1. Ability to intercept just before a class is load time weaved. In
>>>>> this 'advice', the normal class should be available so that a check
>>>>> can be made for SUID using java reflection.
>>>>> 2. Ability to proceed without weaving if I don't want to weave that class.
>>>>>
>>>>> I don't find a way to do this currently. By the time
>>>>> 'staticinitialization' is intercepted, the class may be weaved
>>>>> already.
>>>>>
>>>>> Again, I don't think this is any problem with AspectJ. It is just
>>>>> something I need and I am checking if you could offer any solution
>>>>> with your knowledge of AspectJ implementation.
>>>>>
>>>>> Thanks,
>>>>> Choudary Kothapalli.
>>>>> _______________________________________________
>>>>> aspectj-dev mailing list
>>>>> aspectj-dev@xxxxxxxxxxx
>>>>> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>>>>>
>>>>
>>>>
>>>> --
>>>> Simone Gianni            CEO Semeru s.r.l.           Apache Committer
>>>> http://www.simonegianni.it/
>>>>
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