ClassCastException On JBOSS OSGI 7.1 - jboss

Question

I use JBOSS OSGI 7.1 for my project.
I have 2 bundle:
usermanagement (service provider)
jerseyBundle (service consumer)
When I deploy and start usermanagement bundle,
Then deploy and start jersey bundle.
jerseyBundle getServiceReference() successful.
Then.
I try to redeploy and restart usermanagement. Then refresh all bundles.
JerseyBundle getServiceReference() with Exception: "ClassCastException"
This is code I use to get service:
public <T> T getService(Class<T> type,List<ServiceReference> _sref) {
try {
ServiceReference sref = bundleContext.getServiceReference(type.getName());
if(sref != null)
{
_sref.add(sref);
}
return type.cast(bundleContext.getService(sref));
} catch (Exception ex) {
ex.printStackTrace();
return null;
}
}
I use blueprint to register services.
I tried to ungetservice but it don't solved this problem.
public void unGetService(List<ServiceReference> _sref) {
try{
while(_sref != null && _sref.size() >0 )
{
System.err.println("==============" + bundleContext.ungetService(_sref.remove(0)));
}
}catch(Exception ex){
ex.printStackTrace();
}
}
Are there any ways to redeploy service provider bundle, don't need redeploy service consumer bundle?

Answer 1

The reason for the observed behaviour may be that OSGi caches the service object by bundle. So if you do bundleContext.getService(sref) then OSGI will store this object internally and always return the same until you do ungetService.
So when you update the service bundle which also contains the interface and refresh the client you will have a new class for the interface. If you now do a cast of an old service object to the new interface the ClassCastException will occur.
One way to cope with this is to only use the service object for a short period of time and then unget it. Like this:
ServiceReference sref = bundleContext.getServiceReference(type.getName());
myO = type.cast(bundleContext.getService(sref));
doStuff(myO);
bundleContext.ungetService(sref)
Of course this is only practicable for infrequent calls as you have some overhead.
The other way is to use a ServiceTracker and react on service additions and removals. So for example you could inject a service into your class which does "doStuff" and remove / replace the service when there are changes. This is quite hard to do on your own though.
In fact this is the reason why there are frameworks like declarative services (DS) or blueprint. These make sure to reinject service and restart your components when services come and go.
As you are already using blueprint on the provider side you might try to use it on the client side too. The blueprint client should not have the problems you observed.
Btw. blueprint and DS handle service dynamics very differently. Blueprint injects a proxy once and then just replaces the service object inside the proxy while DS will really restart your user component.