ClassCastException due to Class Loader problem

Question

interface A
class B implements A

I am getting ClassCastException in casting B to A. Both A and B are in the same bundle.

This could be because of the class loader. Why is the class loader getting changed for the same bundle? How can I handle this problem?

Additional information

interface A (ie AdminService) and the implementation class B (ie AdminServiceImpl) are in the same package (fusion-core)
Whereas the casting is happening in a different package. --The casting is not happening directly. ie B b = new B(); A a = (A) b; is not happening.

Casting is happening by resolving a service at OSGi service registry. ie

AdminService adminService = getService(AdminService.class.getName(), 100); 
public T getService(String type, long timeToWait) { 
  ServiceTracker serviceTracker = serviceRegistry.get(type); 
  if (serviceTracker == null) { 
    serviceTracker = this.registerServiceTracker(type); 
  } 
  T service = null; 
  try { 
    service = (T) serviceTracker.waitForService(timeToWait); 
  } catch (InterruptedException e) { 
    logger.error("Error while fetching service", e); 
  } return service; 
}

Epilog

Thank you Ivan, Angelo and BJ. Actually BJ's pointer helped me to fix the problem.

In the manifest of the bundle which was trying to perform the cast, <EXPORT-PACKAGE> was exporting the package of the other bundle which contained the interface and the implementation. Because of this probably the same byte code was getting loaded by the two different class loaders. Bundle (performing the cast) probably assumed the package to be a part of itself and loaded the byte code again !!!

Thanks a lot guys.

Which bundle code that tries to cast is located in? In the same bundle as "B" and "A" or it is a different bundle? — Ivan Dubrov
– Ivan Dubrov, Commented Apr 26, 2011 at 15:02
As Ivan says, we will need a little more information. Can you show the contents of your bundle, and its manifest? — Angelo van der Sijpt
– Angelo van der Sijpt, Commented Apr 26, 2011 at 16:24
in the future, please edit your question rather than including pertinent details in comments. — Shog9
– Shog9, Commented Apr 28, 2011 at 17:12

BJ Hargrave · Accepted Answer · 2011-04-26 16:55:35Z

4

If the code performing the cast to A has loaded a different A than the bundle which defined B (and contains A as you state), then there may be two different A classes in the VM. One from the bundle defining B and another one used by the bundle performing the cast to A.

Since A is a shared type, you need to make sure that the bundle defining B and the bundle casting to A are both using the same class A. They should both either import the package containing A from some 3rd bundle or the bundle defining B should export the package containing A so the bundle performing the cast to A can import that package.

answered Apr 26, 2011 at 16:55

BJ Hargrave

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