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From "Michael Dick (JIRA)" <j...@apache.org>
Subject [jira] Created: (OPENJPA-311) Problem loading classes with OSGi classloaders
Date Thu, 09 Aug 2007 19:51:42 GMT
Problem loading classes with OSGi classloaders
----------------------------------------------

                 Key: OPENJPA-311
                 URL: https://issues.apache.org/jira/browse/OPENJPA-311
             Project: OpenJPA
          Issue Type: Bug
    Affects Versions: 0.9.7, 0.9.6, 0.9.0, 1.0.0
            Reporter: Michael Dick
            Assignee: Michael Dick
             Fix For: 1.0.0


The root of the problem appears to be in the GeneratedClasses.getMostDerivedLoader method.


GetMostDerivedLoader takes two classes (class1 & class2) gets their respective classloaders
(classloader1, & classloader2 respectively) and looks for a match. If the classloaders
are not the same, and neither is null it calls getParent on classloader1 until classloader2
is found, or until there are no more parent loaders. If a match is found the mostDerivedLoader
is considered to be classloader1, if no match is found we use classloader2. 

The problem comes in when you have an OSGI classloader involved. The specific scenario I ran
into has classloader1 calling getParent and encountering an OSGI gateway classloader, but
not classloader2 (which is behind the OSGI gateway). Conceptually classloader2 is a parent
of classloader1, but the OSGI gateway classloader hides it and we aren't able to find it.


I'm probably mangling the OSGI terminology a bit but I think this captures the essence of
the problem. 

It seems to me that the intent of the getMostDerivedLoader is to ensure that we use a classloader
that has the "right" version of class2, preferring classloader1. If that's the case then would
it be possible to just try to load class2 from classloader1 and compare the result to the
original class? I believe this approach would work for OSGI classloaders, but I have a nagging
feeling that I'm missing something. 



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