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From "Marshall Schor (JIRA)" <uima-...@incubator.apache.org>
Subject [jira] Resolved: (UIMA-386) Switching to use correct class loader
Date Tue, 05 Jun 2007 20:17:25 GMT

     [ https://issues.apache.org/jira/browse/UIMA-386?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Marshall Schor resolved UIMA-386.
---------------------------------

    Resolution: Fixed

> Switching to use correct class loader
> -------------------------------------
>
>                 Key: UIMA-386
>                 URL: https://issues.apache.org/jira/browse/UIMA-386
>             Project: UIMA
>          Issue Type: Improvement
>          Components: Core Java Framework
>    Affects Versions: 2.1
>            Reporter: Marshall Schor
>            Assignee: Marshall Schor
>             Fix For: 2.2
>
>
> The current design presumes one classloader is used for all components in an application.
 This shows up in the implementation when using JCas - the class loader used to load the JCas
cover classes is set up in the CAS, and there is only one there.  This works, unless the analysis
engine component is loaded by a different class loader.  This causes strange class-cast exceptions,
where the source and target classes look to be identical (what's happening is that the classes
are named the same, including having the same package names, but are loaded with different
class loaders).  A fix is needed that insures the class loader used for JCas can be switched
when an analysis engine component is run.  This should be time-efficient because the flow
controller could be under a different class loader than the delegates it's controlling, so
the class loader could be switching back and forth twice per delegate dispatch.
> A proposed approach is to add an internal method to the CAS, useClassLoader(xxx), which
will be called by the framework just before the processCas call, passing in the class loader
that was used to load the analysis engine class.  The framework will check to see if this
is the current in-use class loader, and if it is, do nothing.  If it isn't, if the JCas is
instantiated, it will call a new JCas method, switchClassLoader(xxx). This method will (a)
reset the cache JCas uses to reduce object creation for JCas objects, and do what's needed
to load or switch to the right set of iterator generators.  Where possible, re-loading will
be avoided, to make the switch fast.

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