On Dec 1, 2009, at 11:16 AM, Ziegenlippe wrote:
Nice. Does this mean I have to take care about serialization by my
own? I use great libs XStream and Hazelcast. Both of them are doing
a good serialization job. But I see without bundle-id+version there
is no way.
Thanks for the answer,
Not necessarily. Some libraries support the injection of custom hooks
at various stages of the serialization/deserialization process.
As an example, I was able to create OSGi-aware versions of
Object{Output,Input}Stream by overriding the annotateClass() and
resolveClass() methods, respectively.
I'm not familiar with XStream, but it wouldn't surprise me if it
offered some way to influence the class loading process..
As for Hazelcast, I actually went down that path and got it to work by
registering custom serializers which used the OSGi-aware object
streams I talked about above.
Here's the activator I used:
package com.hazelcast.osgi;
import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.packageadmin.PackageAdmin;
import com.hazelcast.core.Hazelcast;
import com.hazelcast.nio.Serializer;
public class Activator implements BundleActivator {
public void start(BundleContext context) throws Exception {
ServiceReference ref =
context.getServiceReference(PackageAdmin.class.getName());
PackageAdmin pkgAdmin = (PackageAdmin) context.getService(ref);
Serializer.registerTypeSerializer(new OsgiObjectSerializer());
Serializer.registerTypeSerializer(new
OsgiDataSerializer(pkgAdmin));
}
public void stop(BundleContext context) throws Exception {
Serializer.registerTypeSerializer(new
Serializer.ObjectSerializer());
Serializer.registerTypeSerializer(new
Serializer.DataSerializer());
Hazelcast.shutdown();
}
}
The implementations of OsgiObjectSerializer and OsgiDataSerializer are
pretty similar to the versions that come with Hazelcast; they simply
inject a bundle name into the stream during serialization, and during
deserialization use that name to lookup the bundle to use to load the
class..
Kris
Andy
Kris Pruden schrieb:
I had a similar problem. The solution boils down to delegating to
the "owning" bundle to load the class. To do this you need of
course to know the name of the bundle. In my case I was able to
solve this problem with a couple helper methods that wrap the
PackageAdmin service provided by OSGi:
public String getBundleName(Class<?> cls) {
Bundle bundle = pkgAdmin.getBundle(cls);
if (bundle != null) {
return bundle.getSymbolicName();
} else {
return null;
}
}
public Class<?> loadClass(String className, String bundleName)
throws ClassNotFoundException {
Bundle[] bundles = pkgAdmin.getBundles(bundleName, null);
if (bundles == null || bundles.length == 0) {
return null;
}
return bundles[0].loadClass(className);
}
When serializing the object, you can use getBundleName to get the
name of the bundle which "owns" the class being serialized. This
name needs to be included in the xml data you store. Then on
deserialization, loadClass looks up the bundle by the name
specified, then uses that bundle to load the class.
This code assumes that there will be only one version of the bundle
with a given name present, but it would be fairly straightforward
to extend this to look at bundle versions if needed...
HTH...
Kris
On Dec 1, 2009, at 10:44 AM, Ziegenlippe wrote:
Hello,
I cannot find a satisfying solution to a simple looking problem
for quite a while.
The condensation of the problem:
Bundle A
the producer stores objects as xml files (e.g. with XStream)
it exports the /bundle.a/ package which contains the interface /
Item/ it contains a private implementation package /
bundle.a.impl/ which contains the item implementation class /
ItemImpl/
Bundle B
the consumer needs to load and process /Item/ instances
therefor it imports package /bundle.a/ which contains the /Item/
interface
Problem: loading Item instances in bundle B leads always to
ClassNotFoundExceptions
Even working with the last resort /DynamicImport-Package: * / does
not solve the problem since it imports only exported packages.
From some hints in the internet I got the feeling that this issue
is not really solved for OSGI. Is there any solution known? How
deal others with that issue e.g. ActiveMq which claims to be OSGI
compliant.
Or am I just on the wrong way?
Thank you in advance,
Andy
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