Re: [aspectj-users] LTW and annotations

[Simone Gianni <simoneg@xxxxxxxxxx>]

Hi Janos,
unfortunately, at least AFAIK, there is no method in ClassLoader to find
"all resources" in a package. The getResource (findResource,
findResources etc..) only find resources if you already know the
complete name of them (complete package). A number of tricks exists,
like obtaining the path of the jar, then opening it as if it was a zip
file, and scanning its content .. but they are not applicable in an
"enterprise" like environment, where a hierarchy of classloaders may be
in place and no direct access to jar files is possible (or even, there
are no jar files at all). I also feel like this is a problem, but it's a
ClassLoader problem in general, nothing AspectJ can easily fix.

Anyway, exploring all possible classes for the presence of an annotation
would be far too heavy. In even a simple web project there can be
thousands of classes, scanning all of them so see which are aspects
before even starting the "main" could require several seconds if not
minutes.

I can't think of any way to avoid the .xml file, maybe there is one, but
without explicit support from the ClassLoader interface or some other
java compiler internals (like a quick way to find all classes having a
specific annotation, that would benefit quite a bit also JPA providers
for example, which are also bound to XML based class listings in most
cases) I think it's hard to do it in a reliable and standards compatible
way. I don't think even a standard annotation processor could somehow
ease this.

Simone

Háber János wrote:
> Hmm!
>
> Tanks.
>
> " but have no idea that it exists an aspect"?
>
> Maybe a solution: Spring solve this probelm with a very simply way.
> Get the selected package (maybe in aspectj possible using <include>
> for this) and get all file-s and directories with
> classloader.getResource method. And if the selected class is an
> @Aspect... load it...
>
>
> Janos
>
>
> -----Original Message-----
> From: aspectj-users-bounces@xxxxxxxxxxx
> [mailto:aspectj-users-bounces@xxxxxxxxxxx] On Behalf Of Simone Gianni
> Sent: Thursday, October 02, 2008 3:17 PM
> To: aspectj-users@xxxxxxxxxxx
> Subject: Re: [aspectj-users] LTW and annotations
>
> If I understand how LTW works correctly, the problem is in class
> loading.
>
> Consider the situation where you have a bean with a doSomething
> method,
> and then have an advice that does something before that method.
>
> You application starts, it will load the bean with a new Bean(). At
> this
> point, the class loader loads the bean, but have no idea that it
> exists
> an aspect, so will not weave the bean. This is because, you never call
> (and have explicitly no way) to call "new MyAspect()".
>
> In fact, if you had such a way of instantiating aspects, another
> situation could arise and cause problems. Suppose you have also a
> tracing aspect, that will intercept all calls to all methods. If this
> tracing aspect gets loaded AFTER the bean has already been loaded, the
> class loader is not able anymore to modify the bean, because it has
> already been loaded.
>
> (in reality, there are some ways to do class redefining in recent
> classloaders, but that brings another lot of problems)
>
> So, yes, you have to define your aspects in the aop.xml file. Since
> this
> is tedious, the ajc compiler can perform this task for you. If you are
> using AJDT in Eclipse, there is an option for generating aop.xml on
> the
> fly under the AspectJ section of you settings. If you are compiling
> from
> command line using ajc, the -outxml option will generate it for you
> (see
> http://www.eclipse.org/aspectj/doc/released/devguide/ajc-ref.html ).
> Also, the maven2 plugin for aspectj will generate the aop.xml file for
> you.
>
> Hope this helps,
> Simone
>
>
>
> Háber János wrote:
>   
>> Hi!
>>
>> I have a question. I want to write an application. I using javaagent
>> vm option to LTW. But in this case what needed in aop.xml (aop.xml
>> required in this case if I not want to set any special weaving
>> options?)
>> If I only write:
>> <aspectj>
>>     <weaver options="-verbose -showWeaveInfo"/>
>> </aspectj>
>>
>> I get: "no aspects registered. Disabling weaver for class loader..."
>> WTF? I need to set the aspects both aop.xml and annotation in java
>> file? Why?
>> If Yes, why? The classloader can't detect the annotations?
>>
>>
>> Janos Haber
>>
>> _______________________________________________
>> aspectj-users mailing list
>> aspectj-users@xxxxxxxxxxx
>> https://dev.eclipse.org/mailman/listinfo/aspectj-users
>>   
>>     
>
>
>   


-- 
Simone Gianni            CEO Semeru s.r.l.           Apache Committer
MALE human being programming a computer   http://www.simonegianni.it/