How to share dependant jars across rars & ears / avoid classcast exceptions

Question

<b>How can one share dependant jars between a ear application and a resource adapter and avoid getting a ClassCastException? </b>
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In some appservers(such as Oracle) the resource adapter is the parent of your ear classloader, so a single instance multiple classloader problem doesn't occur. But in some appservers such as BEA Weblogic this isn't the case. Not sure why BEA decided to make resource adapter class loader seperate and not the parent of ear loader...
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If I bundle the resource adapter specific classes in the corresponding module archive file, I will get a class cast exception, becos I will have a <i>single instance and multiple class loader situation</i> (assuming resource adapters uses its own classloader).
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Second question related to the above: Web logic documentation recommends that we bundle the common files in APP-INF direcotory for embedded resource adapter apps. If I start bundling the resource adapter in an ear file, for every ear app we will have a rar bundled. What about the JNDI names? won't you have to rename the resource adapter differently for each ear so that there is no jndi name clash? Doesn't this defeat the purpose of having one common connector for all apps?
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Here is a detailed description of what I want:
Let say you have a ear file. Let's say there is a common.jar shared between your ear application (say the ejb module uses it), and your resource adapter.
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In the case of Oracle's OC4J I can see there won't be any problem of having this common.jar part of the resource adapter(RA). When the RA class loader loads the rar, it makes sure the common.jar files are accessible in the chain of all class loaders it is a parent of. So, the ear loader, ejb loader etc...will have visibility -> hence no class cast exception.
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But what do clients do when they want to have their ear deployable across multiple appservers not just oc4j. BEA recently changed their class loader structure...their resource loader is no longer parent of the ear, so the ejb app in the ear doesn't have visibility into common.jar packaged with rar. So, the only solution was to bundle the common.jar file with the ear. But this causes problems, because we can have a situation where certain object instances (that are not serialized or copied) can be shared across class loaders. This ends up in the single instance multiple class loader situation->hence classcastexception.
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The only solution I found was to make the common.jar file a shared library. That way only one copy of the class files are there for both the rar and the ear and its visibility is there not only for rar but for ear since it is loaded by the system class loader or shared library class loader (if ther eis one such).
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Please convey best practise recommendation.
Sudhakar

Answer 1

Pete <[email protected]> wrote:
Is there a way to have a non-EJB jar at the EJB classloader level ? Sure, just add it to the Class-Path: manifest entry in your ejb.jar.
Dimitri