Gregg,
Just thought I'd bring this back from previous list discussion, as it
displays some of the issues you had to overcome.
Cheers,
Peter.
Gregg Wonderly wrote:
Okay, I've done some more digging and thinking and one of the primary
issues I believe, comes down to how "containers", whether they are
IDEs, standards like OSGi or JEE etc, provide access to the
"classpath" of the running environment.
At the root of the behavior of PreferredClassProvider is
private static ClassLoader getRMIContextClassLoader() ...
which just gets the context class loader. This loader becomes the
parent of the created PreferredClassLoader.
One of the issues for me, is that I think that honoring the
PREFERRED.LIST is an important part of bringing advertised services
into any JVM.
The primary driver of the use of PreferredClassProvider is of course
the user of the RMIClassLoaderSpi class in the RMIClassLoader. In
reggie, the places that deal with unmarshalling, are using
MarshalledInstance, MarshalledWrapper and MarshalInputStream to
package this activity.
But, what I am seeing in netbeans is that reggie's unmarshalling is
using the JVM system class loader as the parent, and that's causing
non-preferred classes to be resolved in that class loader. However,
my netbeans modules have a different copy of the jsk-platform.jar that
is visible to them, and that's where they are resolving things like
Matches and other classes that are at the core of service
unmarshalling by reggie.
So, I am trying to gather some more information to have some better
perspectives on what actually makes the most sense.
Technically, netbeans sets the context class loader to the "netbeans"
system class loader. In most of my jini applications, I always use
Thread.currentThread().setContextClassLoader(
getClass().getClassLoader() )
in newly created threads and in EDT listener objects (via the
SyncThread class at http://swingutil.dev.java.net). I think this
should make things work out in integrating Jini into netbeans too, but
I've somehow not recognized the right problem yet and got it solved.
Gregg Wonderly
Niclas Hedhman wrote:
On Thu, Oct 15, 2009 at 12:42 AM, Gregg Wonderly <gr...@wonderly.org>
wrote:
Anyone have thoughts or questions?
For OSGi (maybe Netbeans as well) there might be additional
"problems", since "loading a class" is not a straight forward process
of calling a static provider. In OSGi, each "module" is wired up with
a "class space" but the same class name (difference version, different
provider, etc) may be in another "class space" in other modules. So,
to fulfill a contract where a static method gets called from
"anywhere" and I need to figure out which class to load is near
impossible (at least in a platform independent way) in OSGi, as you
will have to figure out which bundle (module) the caller reside in, in
an environment where multiple versions of the same class can exist.
(The reason this is near impossible is that the OSGi spec doesn't have
any Classloader API, from which the Bundle can be retrieved.)
"Class space" is a complex and powerful concept in OSGi, which
basically try to ensure that there are no class version clashes and
yet provide the class visibility needed.
OTOH, Paremus has shown that
a) Locally available classes can be used,
b) Remote classes be downloaded and wrapped in temporary bundles with
OSGi contracts honored.
c) PreferredClassLoader is not needed.
So, perhaps your ambitions are too great and that you can/should
ignore OSGi's needs.
Cheers
