[
Date Prev][
Date Next][
Thread Prev][
Thread Next][
Date Index][
Thread Index]
[
List Home]
|
Re: [aspectj-dev] Can I intercept before a class is load time weaved
|
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/
>>>>>
>>>>> _______________________________________________
>>>>> aspectj-dev mailing list
>>>>> aspectj-dev@xxxxxxxxxxx
>>>>> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>>>>>
>>>> _______________________________________________
>>>> aspectj-dev mailing list
>>>> aspectj-dev@xxxxxxxxxxx
>>>> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>>>>
>>> _______________________________________________
>>> aspectj-dev mailing list
>>> aspectj-dev@xxxxxxxxxxx
>>> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>>>
>> _______________________________________________
>> aspectj-dev mailing list
>> aspectj-dev@xxxxxxxxxxx
>> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>>
> _______________________________________________
> aspectj-dev mailing list
> aspectj-dev@xxxxxxxxxxx
> https://dev.eclipse.org/mailman/listinfo/aspectj-dev
>
