IOC class loading issue in OSGi
-------------------------------
Key: TAP5-1424
URL: https://issues.apache.org/jira/browse/TAP5-1424
Project: Tapestry 5
Issue Type: Bug
Components: tapestry-ioc
Affects Versions: 5.1.0.5, 5.2.4
Reporter: Richard Schurig
Priority: Critical
we're using Tapestry IOC in an OSGi environment (Equinox 3.4) and recently
discovered some serious class loading issues when installing multiple versions
of the Tapestry Jars (5.1.0.5 and 5.2.4).
the problem itself lies in the class ClassFactoryClassPool, which picks up
every class loader from every class it ever sees. this completely bypasses the
OSGi way of class loading!
see the 2 attached bundles for an example: bundle A is using T5.1 and bundle B
is using T5.2. but B is also using imports from A for implementing a service,
an every day scenario in OSGi. now what happens: the IOC registry starting in
bundle B is proxying some class in its bundle, which has references to a class
in A. this results in ClassFactoryClassPool picking up the class loader of
bundle A also and therefore seeing all T5.1 classes. so you end up with two Tap
versions in allLoaders, and it's just a matter of timing, if you have a working
sequence in the chain.
i managed to produce a non working sequence that raises an exception:
Caused by: compile error: getCoercion(java.lang.Class,java.lang.Class) not
found in org.apache.tapestry5.ioc.services.TypeCoercer
this happens because the T5.1 classes are picked instead of T5.2 in bundle B
and getCoercion did not exist in that version. but T5.1 should not be visible
to bundle B since it neither includes nor imports its classes.
the solution seems to be just using the thread context class loader, which
(properly set) provides all the classes needed by IOC, at least in OSGi. i
tested the solution by modifying ClassFactoryClassPool like that:
public ClassFactoryClassPool(ClassLoader contextClassLoader)
{
super(null);
ClassPath path = new LoaderClassPath(contextClassLoader);
insertClassPath(path);
}
public synchronized void addClassLoaderIfNeeded(ClassLoader loader)
{
// Just do nothing
}
This worked for me: in the first place a lot of "ClassNotFoundExceptions"
occurred, revealing all the classes that we're accessible by bypassing the OSGi
bundle class Loader, but after adding them to the imports of my bundle,
everything was fine.
as i did not understand the purpose of the sophisticated class loader handling,
i assume that the above is not a fix option. but maybe some kind of switch can
be implemented, that turns off class loader collecting on demand.
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