rashid wrote:when I try to instantiate the new DbReaderConnection class which I called JenaDbReaderConnection from the DBReaderNodeModel class (which I called JenaDBReaderNodeModel), I am having a class not found exception from the class loader. I wonder why is that? Does Knime uses it's own class loader to load the class and is there any security check or some thing that causes the class loader not to load the new JenaDatabaseReaderConnection class. Can some one shed some light on this issue.

There is an issue with class loading in Eclipse when a class in plugin A wants to load a class in plugin B and plugin A does not depend on plugin B, because each plugin uses its own classloader. That is for example the case with all NodeFactories. They are instantiated from the org.knime.core-plugin when a workflow is loaded but reside in some other plugin which the core-plugin does not depend on. I'm not sure if this is the case in your example. But you may try to use KNIME's GlobalClassCreator to load a class which queries all plugins' classloaders.
If however, all classes your are dealing with are in the same plugin, this should work in any case out-of-the-box. Which class excactly is not found? Any of your own classes or any of the Jena classes. Maybe they are in a JAR-file and the JAR-file is not listed in the Runtime-classpath of your plugin? Adding a JAR to the Project Libraries (via Project Properties -> Libraries) does not work when you are dealing with plugins, the JARs must be listed in the MANIFEST.MF under Bundle-ClassPath instead.

Regards,

Thorsten

In order to use a 3rd party lib, do the following
Create a "/lib" directory in your project and copy the 3rd-party lib (the .jar) there.
In your plugin.xml file (in the root of your project) add the jar to the classpath Tab "Runtime", section "Classpath", use "Add..." and browse to your lib.

Another common mistake is to not export the package that contains the NodeFactory (depending on when you get the error message). In the same "Runtime" tab, "Add..." the package your JenaDBReaderNodeFactory is located in (the one that is registered with the node extension point of KNIME's node repository).

Also, make sure the jar that is build for your project (defined in the "Build" tab, section "Runtime Information"), is listed in the "Classpath" section of the "Runtime" tab. If it doesn't appear here, use "New..." to add it.

I hope these things help resolving your problem.
Best regards.
- Peter.

As a side note The KNIME workbench is not using it's own special classloader, it is using the loader that comes with Eclipse and its plug-in mechanisms.