Switching to use correct class loader
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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
Assigned To: 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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