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Re: [aspectj-dev] Can I intercept before a class is load time weaved
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I haven't tried it, but from the code this looks like it would work
<weaver options="-XaddSerialVersionUID"/>
if that doesn't work, let me know and we'll fix it up. Sorry I didn't
think of this earlier when you were describing your problem, it is
what the feature was designed for.
cheers
Andy
2009/9/20 Choudary Kothapalli <choudary.kothapalli@xxxxxxxxx>:
> But I am using load time weaving and I do not see
> -XaddSerialVersionUID supported at LTW. Is it?
>
> Thanks,
> Choudary.
>
> On Fri, Sep 18, 2009 at 6:38 PM, Andy Clement <andrew.clement@xxxxxxxxx> wrote:
>> 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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