> -----Original Message-----
> From: Stephen McConnell [mailto:[EMAIL PROTECTED]
> Sent: Thursday, January 01, 2004 3:53 PM
>
> Olaf Bergner wrote:
>
> >>-----Original Message-----
> >>From: Niclas Hedhman [mailto:[EMAIL PROTECTED]
> >>Sent: Wednesday, December 31, 2003 2:39 AM
> >>
> >>I "wild" guess;
> >>The (Kernel) cast would then implicitly load the merlin-api jar, which
> >>probably then conflicts with the merlin-api being loaded by the
> >>avalon-repository system.
> >>
> >
> >Probably something along those lines. Doubt that I will ever find out. I
> >tried to follow your advice and traced all classloading events during the
> >testcase. To that end I wrote a custom classloader which simply spat out
> >which class was currently being loaded and if the effective
> class loader was
> >the parent classloader or this classloader. This gave me a whole lot of
> >info, albeit nothing useful. At least not for me. My faithful classloader
> >was tracing and tracing and then, right out of the middle of
> nowhere there
> >was this good ol' LinkageError again.
> >
> >But then again, I had a look at the source for java.lang.ClassLoader and
> >java.net.URLClassLoader. At least I learned a bit from this one.
> >
>
> Olaf:
>
> Including container implementation jars in a project.xml will cause
> problems due to classloader logic in the JRE. The problem is that if an
> implementation class is included in the project.xml, then it going into
> a classloader constructed by maven. When you kernel or something like
> the AMTC kicks in the avalon-repository package is constructing a child
> classloader with the complete set of implementation resources - however,
> if an implementation class in merlin invokes an operation on another
> class, and if the other class is in the maven classloader, and the other
> class invokes an operation on a third class (which would normally be in
> the merlin classloader), it will not be found. This is because class
> lookup is always up relative to the classloader associated with the
> class making the invocation.
>
Makes sense. Thanks for that info. It's a little mind boggling at first
sight but cannot possibly be harder than group theory. Still it's slippy
ground.
> The solution (that will let you get back to normal code and avoid
> reflection) is to declare a factory. So instead of using the repository
> package to load merlin you should use the repository package to load
> your own factory. The repository package will then create the
> classloader you need with everything in it and your dependencies in
> project.xml can be reduced down to nothing more than
> avalon-repository-main.
>
Thanks. I'll give it a try. Yet I think I'll have to get my head around some
of the deeper merlin/repository mysteries first. Do I understand you
correctly in that you are talking about replacing
Artifact artifact =
DefaultBuilder.createImplementationArtifact(
classloader,
getMerlinHome(),
getBaseDirectory(),
MERLIN_PROPERTIES,
IMPLEMENTATION_KEY);
String[] hosts = getHosts();
InitialContext context =
new DefaultInitialContext(repository, hosts);
Builder builder = new DefaultBuilder(context, artifact);
m_classloader = builder.getClassLoader();
Factory factory = builder.getFactory();
where artifact represents a merlin kernel with some code so that artifact
represents a merlin kernel *factory*? But as soon as I switch from using
reflection in my testcase to the 'normal' way, e.g. as soon as I do
something like
final Kernel meLovelyKernel = (Kernel) factory.create(criteria);
I'll be back to where I came from: maven's got to see the Kernel interface,
and thus merlin-api's got to be in project.xml. Or did I get it all wrong?
Please bear with me, but I definitely want to get this one straight since
it's really been bothering me for quite a while.
And now for something completely different: hope you and your's had a nice
New Year's Eve. No misbegotten classloaders lurking on the bottom of some
champagne bottle. All the best for a new year.
>
> Cheers, Stephen.
Cheers,
Olaf
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