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context class loader [message #708182]

Tue, 02 August 2011 10:46

Vladimir Stevanovic is currently offline

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

BundleWebappClassLoader is set as the thread context class loader. I understood that it was created by synthetic context bundle, which imports all bundles in the scope, so context class loader would have to load any class from the scope.
I'm using some third party library, which uses classloader.loadClass() method and it cannot find the class. And, when thread context loader (BundleWebappClassLoader ) is inspected in the debugger, the field "classes" is empty!
Bug?

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Re: context class loader [message #708198 is a reply to message #708182]

Tue, 02 August 2011 11:03

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

Do you mean that the third party library uses the context class loader for loading? If so it should be able to find the resources accessible by the synthetic context.

In other words the library should explicitly use the context class loader, since Java will not make use of it by default.

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Re: context class loader [message #708202 is a reply to message #708198]

Tue, 02 August 2011 11:06

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

Yes it uses the context class loader, but the loader doesn't load the class.

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Re: context class loader [message #708331 is a reply to message #708202]

Tue, 02 August 2011 13:45

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

Can you check if the class can be loaded from the any loader in the user region (clload) and from the loader of the bundle/webapp (clload with id) and post the results?

You can find how to do this in Virgo FAQ.

[Updated on: Tue, 02 August 2011 16:00]

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Re: context class loader [message #708811 is a reply to message #708331]

Wed, 03 August 2011 03:39

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

I've checked and class is loaded by several bundle loaders, but particular bundle cannot load the class.

The "third part library" is actually a javax.xml.transform in the org.eclipse.osgi bundle. The context class-loading is performed in the FactoryFinder.

When I replaced the original context classloader, and put one of the bundle classloaders that can load the class, everything worked, so I guess the problem is in BundleWebappClassLoader.

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Re: context class loader [message #708888 is a reply to message #708811]

Wed, 03 August 2011 05:01

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

If your bundle cannot load the needed class what you can do is to:

extend your web classpath header to include the resource
import the needed class from another bundle

[Updated on: Wed, 03 August 2011 05:01]

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Re: context class loader [message #709004 is a reply to message #708888]

Wed, 03 August 2011 07:48

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

Ok, but I still don't understand why is BundleWebappClassLoader set as context classloader. What about classloader from the synthetic context bundle?
I thought that synthetic context CL is always set as a thread context classloader, as it was stated here:
http://underlap.blogspot.com/2011/02/thread-context-class-loading-in-virgo.html

[Updated on: Wed, 03 August 2011 07:48]

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Re: context class loader [message #709088 is a reply to message #709004]

Wed, 03 August 2011 09:46

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

The synthetic context is used for PAR or scoped plan. Virgo builds a synthetic bundle and sets its loader as context class loader for all artefacts in the scope.

What's the packaging you are using - is it a PAR or a plan? Do you have a web app inside the PAR/plan?

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Re: context class loader [message #709121 is a reply to message #709088]

Wed, 03 August 2011 10:17

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

I'm using PAR packaging, with one WAB bundle and several regular bundles.

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Re: context class loader [message #709807 is a reply to message #709121]

Thu, 04 August 2011 06:24

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

The webapp classloader (CL) is set by Tomcat on request (as by spec). Therefore the synthetic thread context CL from the PAR is overwritten with the webapp one. There may be applications that rely on this behaviour so we can't do much in this direction.

One thing that comes to my mind is to add the needed import(s) to your webapp so the FactoryFinder can load the class from the webapp CL.

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Re: context class loader [message #709817 is a reply to message #709807]

Thu, 04 August 2011 06:41

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

Thanks for the explanation.
I'm just wondering is there any way to obtain synthetic thread context CL, in case I'd like to replace (and later to restore) the web CL ?

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Re: context class loader [message #709971 is a reply to message #709817]

Thu, 04 August 2011 10:44

Hristo Iliev
Messages: 152
Registered: May 2010
Location: Sofia, Bulgaria

Senior Member

Unfortunately there's no API to do this.

I created enhancement [1] to cover this as well as bug [2] so we can document your question for the scope and context class loaders.

[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=353899
[2] https://bugs.eclipse.org/bugs/show_bug.cgi?id=353897

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Re: context class loader [message #710009 is a reply to message #709971]

Thu, 04 August 2011 11:24

Vladimir Stevanovic
Messages: 28
Registered: March 2010

Junior Member

Great,
thanks

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