[rules-users] NoClassDefFoundError: BaseObjectClassFieldReader

Michal Bali michalbali at gmail.com
Fri Dec 5 18:01:42 EST 2008 

I vaguely remember reading about similar issues with OSGi. It was solved by
using so called "buddy loading":
http://help.eclipse.org/ganymede/topic/org.eclipse.platform.doc.isv/reference/misc/buddy_loading.html
Hope it helps.

On Fri, Dec 5, 2008 at 10:11 PM, Faron Dutton <fgdutton at gmail.com> wrote:

> Once I work out the kinks, I could provide the code (e.g.,
> ClassLoaders) on the wiki.
>
> Unfortunately, Drools cannot anticipate dependencies and there is no
> special sauce for adding them at runtime. It would be nice if Drools
> was more consistent in its use of ClassLoader. I know this is vague;
> I'll try to provide some example later. Its been about two weeks since
> I wrote the solution so I'll need to go back and find them again. MVEL
> appears to be a bigger issue though. The ClassLoader should really be
> associated with the working memory instead of the thread.
>
> On Fri, Dec 5, 2008 at 4:52 PM, Edson Tirelli <tirelli at post.com> wrote:
> >
> >    Thanks a lot for the information. Maybe we should add this to a Wiki
> > page?
> >
> >    From a Drools perspective, a solution like you proposed should work
> for
> > any case, since we also internally tell MVEL to use the same classloader
> > hierarchy... unless there is some unknown bug.
> >
> >    Regarding declaring dependencies, I don't understand how Drools could
> > declare such dependency since the fact classes are defined and provided
> by
> > users and not known by drools in advance. Is there some default mechanism
> > that we could implement to support such things "automagically" in OSGi
> > deployments?
> >
> >    []s
> >    Edson
> >
> > 2008/12/5 Faron Dutton <fgdutton at gmail.com>
> >>
> >> I have successfully loaded rules and facts from other bundles in Eclipse
> >> 3.4.
> >>
> >> I encountered the same issue, which is due to the ClassLoader behavior
> >> defined by OSGi v4. Eclipse 3.3 introduced the new behavior and
> >> Eclipse 3.4 aggressively adheres to the specification. Drools attempts
> >> to access a Class through a reference to a ClassLoader, which by
> >> default is its bundle ClassLoader. MVEL attempts to access a Class
> >> through the context ClassLoader, which OSGi sets to the bundle's
> >> ClassLoader. The problem arises because neither the Drools bundle nor
> >> the MVEL bundle (I have each Drools artifact in a separate bundle)
> >> declare a dependency on the package containing the fact's Class.
> >> Therefore, OSGi does not add that package to the bundle's ClassLoader
> >> and you get a ClassNotFoundException when Drools attempts to find the
> >> Class.
> >>
> >> I worked around this issue by doing several things:
> >> 1) Created an implementation of ClassLoader that delegates to the
> >> bundle (BundleClassLoader).
> >> 2) Created a composite ClassLoader that contains many bundle
> >> ClassLoaders (CompositeClassLoader).
> >> 3) For each bundle containing a rule or fact, wrap it in a
> >> BundleClassLoader and add it to the CompositeClassLoader.
> >> 4) Pass the CompositeClassLoader to the methods mentioned in Edson's
> post.
> >> 5) Wrap the working memory in a Class that sets the context
> >> ClassLoader before each method invocation and restores the original
> >> context ClassLoader afterwards.
> >>
> >> This takes care of most but not all of the issues. Specifically, some
> >> invocations of MVEL still fail but the system works. I am continuing
> >> to investigate a more elegant solution.
> >>
> >> Faron.
> >>
> >>
> >>
> >>
> >>
> >> On Wed, Dec 3, 2008 at 10:11 AM, Edson Tirelli <tirelli at post.com>
> wrote:
> >> >
> >> >    What do you mean by "facts in other plugins"?
> >> >
> >> >    If your facts are loaded by a different classloader hierarchy, you
> >> > need
> >> > to set the facts classloader in:
> >> >
> >> > PackageBuilderConfiguration.setClassLoader();  // to compile the rules
> >> > RulebaseConfiguration.setClassLoader(); // to create the rulebase and
> >> > run it
> >> >
> >> >    []s
> >> >    Edson
> >> >
> >> > 2008/12/2 keithnielsen <keithnielsen at discover.com>
> >> >>
> >> >> Further testing shows that while the rules engine can locate facts
> from
> >> >> other
> >> >> plug-ins (facts located in the same plugin as the rules engine work
> >> >> fine,
> >> >> but not realistic to expect that all facts will be co-located in the
> >> >> same
> >> >> plugin), an attempt to reconstitute them using the
> ByteArrayClassloader
> >> >> will
> >> >> not work. Has anyone been successful using facts located in other
> >> >> plug-ins?
> >> >> I am using Drools 5.M2 with Eclipse 3.4.
> >> >>
> >> >>
> >> >>
> >> >> keithnielsen wrote:
> >> >> >
> >> >> > I have the following rule:
> >> >> >
> >> >> > rule "Retrieve CID Presentation Model"
> >> >> >       ruleflow-group "RetrieveCID"
> >> >> >
> >> >> >       when
> >> >> >
> >> >> >
> >> >> >
> >> >> >
> CIDPresentationModel($cidValue:cidValue,$cidExpirationDate:expirationDate)
> >> >> >       then
> >> >> >               boolean cidResult =
> >> >> > cidService.verifyCIDIsValid($cidValue,$cidExpirationDate);
> >> >> >               CIDResult result = new CIDResult(cidResult);
> >> >> >               insert(result);
> >> >> >               System.out.println("Executing: Retrieve CID
> >> >> > Presentation
> >> >> > Model");
> >> >> > end
> >> >> >
> >> >> > Deep in the bowels of drools there is a call to
> >> >> > ClassFieldAccessorFactory.getClassFieldReader where it attempts to
> >> >> > create
> >> >> > a class using the byte array classloader, i.e. final Class<?>
> >> >> > newClass =
> >> >> > byteArrayClassLoader.defineClass(className,
> bytes,PROTECTION_DOMAIN).
> >> >> > Its
> >> >> > at this point that a NoClassDefFoundError on the
> >> >> > BaseObjectClassFieldReader. From what I understand of
> >> >> > NoClassDefFoundError
> >> >> > it can result when there are two sources of the same class in the
> >> >> > classpath or if there is some reference from the class resulting in
> >> >> > the
> >> >> > error to another class that can not be resolved. It only appears in
> >> >> > situations where there is fields involved. It doesnt seem to matter
> >> >> > how
> >> >> > simple the object is, the minute I try to use field assignment it
> >> >> > throws
> >> >> > an error.
> >> >> >
> >> >> > The rules engine is running as an Eclipse plug-in.
> >> >> >
> >> >>
> >> >> --
> >> >> View this message in context:
> >> >>
> >> >>
> http://www.nabble.com/NoClassDefFoundError%3A-BaseObjectClassFieldReader-tp20802217p20806634.html
> >> >> Sent from the drools - user mailing list archive at Nabble.com.
> >> >>
> >> >> _______________________________________________
> >> >> rules-users mailing list
> >> >> rules-users at lists.jboss.org
> >> >> https://lists.jboss.org/mailman/listinfo/rules-users
> >> >
> >> >
> >> >
> >> > --
> >> >  Edson Tirelli
> >> >  JBoss Drools Core Development
> >> >  JBoss, a division of Red Hat @ www.jboss.com
> >> >
> >> > _______________________________________________
> >> > rules-users mailing list
> >> > rules-users at lists.jboss.org
> >> > https://lists.jboss.org/mailman/listinfo/rules-users
> >> >
> >> >
> >> _______________________________________________
> >> rules-users mailing list
> >> rules-users at lists.jboss.org
> >> https://lists.jboss.org/mailman/listinfo/rules-users
> >
> >
> >
> > --
> >  Edson Tirelli
> >  JBoss Drools Core Development
> >  JBoss, a division of Red Hat @ www.jboss.com
> >
> > _______________________________________________
> > rules-users mailing list
> > rules-users at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/rules-users
> >
> >
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