Re: [aspectj-users] staticinitialization and target class

[Simone Gianni <simoneg@xxxxxxxxxx>]

Hi Mohammad,

I've found this page : http://java.decompiler.free.fr/?q=node/118 , it seems that JD produces the raw bytecode commented when it is not able to decompile it properly, which means that it is JD giving the error, not the code itself in error. I haven't been using JD lately, so I can't remember how to configure it properly, but the bytecode seems correct, so the problem must be somewhere else.

Simone

2010/4/28 Simone Gianni <simoneg@xxxxxxxxxx>

Hi Mohammad,

mmm ... the decompiled bytecode seems correct : it creates a joinpoint static part, then executes the previous static initializer (which is empty), and then calls the after advice both when an exception is raised and when no exception is raised.

Bytecode, AFAIK, cannot be commented out, is that the output of javap, dj or which other tool?

Obviously, static initializer is executed only when the class is loaded for the first time in the JVM, if it is not loaded it will not be called and the class not be registered. Java lacks a serious "service discovery" system, cause for backward compatibility with applets classloaders does not have a method for "listing" the classpath, not to mention to list which classes are annotated with a specific annotations. Apt is the tool that can ease this pain, creating a text file from classes annotated with a specific annotation, but unfortunately it works at compile time, not at runtime, that's why there is still the need for files like persistence.xml in JPA and web.xml in jars.

To make a long story short, as Andy did in his code, somewhere you must still call "new ClassUnderObservation()" or at least Class.forName("com.foo.ClassUnderObservation") or access a static field or method of that class to get it loaded by the jvm, otherwise no static init, no registration in the aspect.

Simone 

2010/4/28 Andy Clement <andrew.clement@xxxxxxxxx>

You didn't mention how it fails??  Here is Simones code in a real
program, appears to work.  What is different about your code or that
particular type?  Perhaps narrow your pointcut to a specific type to
test the registration logic is working before expanding it to cover
more types?

=== A.aj ===
package com.foo;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.*;

import org.aspectj.lang.reflect.InitializerSignature;

@Retention(RetentionPolicy.RUNTIME)
@interface Observer {}

aspect A {
       public static void main(String[] args) {
               new C();new D(); new E();
       }

  static List<Class> registry = new ArrayList<Class>();

  pointcut observerKlasses(): staticinitialization(@Observer com..*);

       after(): observerKlasses() {
           InitializerSignature initsig =
(InitializerSignature)thisJoinPointStaticPart.getSignature();
           Class klass = initsig.getDeclaringType();
           registry.add(klass);
           System.out.println("Registering "+klass);
       }

}

@Observer
class C {}

class D{}

@Observer
class E {}
===
ajc A.aj
java A
Registering class com.foo.C
Registering class com.foo.E

cheers,
Andy

On 28 April 2010 00:30, Mohammad Norouzi <mnrz57@xxxxxxxxx> wrote:
> Hi Simone,
> Thanks... I did what you said but there is a problem. During the compile
> there is no error but it seems the static block doesn't work. I tried to
> decompile the target class to see what changes AspectJ has applied and I can
> see a static block has been created but it is commented as follow:
>
>
>   // ERROR //
>   static
>   {
>     // Byte code:
>     //   0: new 87    org/aspectj/runtime/reflect/Factory
>     //   3: dup
>     //   4: ldc 88
>     //   6: ldc 90
>     //   8: invokestatic 96    java/lang/Class:forName
> (Ljava/lang/String;)Ljava/lang/Class;
>     //   11: invokespecial 99
> org/aspectj/runtime/reflect/Factory:<init>
> (Ljava/lang/String;Ljava/lang/Class;)V
>     //   14: astore_0
>     //   15: aload_0
>     //   16: ldc 101
>     //   18: aload_0
>     //   19: ldc 103
>     //   21: ldc 90
>     //   23: invokevirtual 107
> org/aspectj/runtime/reflect/Factory:makeInitializerSig
> (Ljava/lang/String;Ljava/lang/String;)Lorg/aspectj/lang/reflect/InitializerSignature;
>     //   26: iconst_0
>     //   27: invokevirtual 111
> org/aspectj/runtime/reflect/Factory:makeSJP
> (Ljava/lang/String;Lorg/aspectj/lang/Signature;I)Lorg/aspectj/lang/JoinPoint$StaticPart;
>     //   30: putstatic 79    com/foo/listener/MyListener1:ajc$tjp_0
> Lorg/aspectj/lang/JoinPoint$StaticPart;
>     //   33: goto +28 -> 61
>     //   36: astore_0
>     //   37: aload_0
>     //   38: instanceof 71
>     //   41: ifeq +8 -> 49
>     //   44: aload_0
>     //   45: checkcast 71    java/lang/ExceptionInInitializerError
>     //   48: athrow
>     //   49: nop
>     //   50: invokestatic 77
> com/foo/aspect/EventDispatcherAspect:aspectOf
> ()Lcom/foo/aspect/EventDispatcherAspect;
>     //   53: getstatic 79    com/foo/listener/MyListener1:ajc$tjp_0
> Lorg/aspectj/lang/JoinPoint$StaticPart;
>     //   56: invokevirtual 83
> com/foo/aspect/EventDispatcherAspect:ajc$after$com_foo_aspect_EventDispatcherAspect$1$5b3bc9fd
> (Lorg/aspectj/lang/JoinPoint$StaticPart;)V
>     //   59: aload_0
>     //   60: athrow
>     //   61: invokestatic 77
> com/foo/aspect/EventDispatcherAspect:aspectOf
> ()Lcom/foo/aspect/EventDispatcherAspect;
>     //   64: getstatic 79    com/foo/listener/MyListener1:ajc$tjp_0
> Lorg/aspectj/lang/JoinPoint$StaticPart;
>     //   67: invokevirtual 83
> com/foo/aspect/EventDispatcherAspect:ajc$after$com_foo_aspect_EventDispatcherAspect$1$5b3bc9fd
> (Lorg/aspectj/lang/JoinPoint$StaticPart;)V
>     //   70: return
>     //
>     // Exception table:
>     //   from    to    target    type
>     //   33    36    36    java/lang/Throwable
>   }
>
> Regards,
> Mohammad
> --------------------------
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>
>
>
> On Tue, Apr 27, 2010 at 7:33 PM, Simone Gianni <simoneg@xxxxxxxxxx> wrote:
>>
>> Hi Mohammad,
>> staticinitialization has no target object because when a class is
>> initialized there is no instance yet. Probably you can obtain the class and
>> other informations using ThisJoinPointStaticPart inside your advice.
>>
>>     pointcut observerMethods():
>>         staticinitialization(@Observer com..*);
>>
>>    after(): observerMethods() {
>>         InitializerSignature initsig =
>> (InitializerSignature)ThisJoinPointStaticPart.getSignature();
>>         Class klass = initsig.getDeclaringType();
>>         // adding 'klass' into Registry
>>    }
>>
>> See http://www.eclipse.org/aspectj/doc/released/runtime-api/index.html for
>> more info.
>>
>> Simone
>>
>> 2010/4/27 Mohammad Norouzi <mnrz57@xxxxxxxxx>
>>>
>>> Hello
>>> I want to register those classes annotated with @Observer in a Registry
>>> class... I want this occurs in a static block of such classes:
>>>
>>>     pointcut observerMethods(Class klass):
>>>         staticinitialization(@Observer com..*)
>>>         && target(klass);
>>>
>>>    after(Class klass): observerMethods(klass) {
>>>         // adding 'klass' into Registry
>>>
>>>    }
>>>
>>> but as I read in manual it is said staticinitialization has no target
>>> object... is this right? if yes, how can I obtain the Class of those
>>> classes. Can I declare a static-block for matching classes?
>>>
>>> thanks
>>>
>>> Regards,
>>> Mohammad
>>> --------------------------
>>> Sun Certified Web Developer
>>> Have a look at some pictures @ http://pixelshot.wordpress.com/
>>>
>>>
>>>
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>>
>>
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