ClassCastException when I access an EJB from a remote EJB in WL 8.1

Question

I am using WebLogic 8.1 and am trying to lookup the home interface for an EJB (_ejbRemote_)
from another EJB (_ejbCurrent_). They are deployed in seperate EARs. When I bundle
the home and remote interfaces for ejbRemote in the EAR file that ejbCurrent
is deployed in, everything works fine. But I need to be able to configure ejbRemote
at run time and my customers don't want to have to bundle their classes in my
EAR. So I invoke a custom classloader (of type java.net.URLClassLoader) that will
load the home and remote interface classes for ejbRemote from a configurable
location at runtime. This finds the classes no problem, and the InitialContext.lookup()
returns a stub, but I get a 'java.lang.ClassCastException: Cannot narrow remote
object' error when I call PortableRemoteObject.narrow(home, homeClass);
The code looks like:
// Assume EJBHomeStr = "com.foo.TestHome" in this case
// Load the home interface class. This works.
Class homeClass = urlClassLoader.loadClass(EJBHomeStr);
// Lookup the home interface. This works.
Object lookedUpHomeObject = initialContext.lookup(JNDIName);
// This fails.
Object homeObject = PortableRemoteObject.narrow(lookedUpHomeObject, homeClass);
And the weblogic error looks like
... ; nested exception is:
java.lang.ClassCastException: Cannot narrow remote object to com.foo.TestHome
at weblogic.iiop.PortableRemoteObjectDelegateImpl.narrow(PortableRemoteO
bjectDelegateImpl.java:219)
at javax.rmi.PortableRemoteObject.narrow(PortableRemoteObject.java:134)
at ...[the rest is just my application code stack...]
When I log the ClassLoaders for the affected objects, using getClass().getClassLoader(),
I get:
<snippet from log follows>
getClass().getClassLoader(): weblogic.utils.classloaders.GenericClassLoader@667da1
finder:
weblogic.utils.classloaders.MultiClassFinder@db9199 annotation: myEJBApp@
homeClass.getName(): com.foo.TestHome classloader = java.net.URLClassLoader@4f1707
lookedUpHomeObject.getClass().getName(): com.foo.Test_EJB_kx82zy_HomeImpl_810_WLStub
classloader = weblogic.utils.classloaders.GenericClassLoader@667da1
finder: weblogic.utils.classloaders.MultiClassFinder@db9199 annotation: myEJBApp@
<end snippet from log>
So it appears that since the looked up Stub was loaded by the WebLogic classloader
and the actual Home class was loaded by my URLClassLoader, the narrow() can't
reconcile the two. I have tried both rmic and the Weblogic appc command to pre-generate
the stubs, which I put in the same JAR as my home and remote interface classes
and load with my custom classloader. But the standard stub (generated by either
rmic or appc) is named TestHomeStub.class and Weblogic is ignoring those and
making a class with the name Test_EJB_kx82zy_HomeImpl_810_WLStub, as shown above.
I have also tried to put the remote interface classes and stubs in the System
classpath using the -classpath option when I start WebLogic, but same result.
The question is, Is there a way in WebLogic to communicate with a remote EJB in
a seperate EAR without bundling anything about that remote EAR in my EAR? Or is
there something I've missed? I need to keep my application J2EE compliant, meaning
I can't hardcode any AppServer-specific code in my application.
Thanks.

Answer 1

Hi Jon,
Glad to hear that.
Regards,
Slava Imeshev
"Jon Sutula" <[email protected]> wrote in message news:[email protected]...
>
I fixed the problem. It turns out I didn't need to use a custom classloader at
all, I just use Reflection directly on the classes ruturned from my JNDI lookup.
So when I lookup the home class, I don't need to narrow or cast it, I just use
Reflection to invoke the "create" method. Then I use the object that I get from
create and directly invoke whatever method on it I need, again using Reflection.
And that works.
"Slava Imeshev" <[email protected]> wrote:
Hi Jon,
The problem is, this class is not available for the classloader
running your "main code".
You can try to hack the into the thread context class loader:
Thread thread = Thread.currentThread();
ContextClassLoader originalClassLoader = thread.getContextClassLoader();
try {
YourURLClassloader yourClassLoader = new
YourURLClassloader(originalClassLoader);
thread.setContextClassLoader(yourClassLoader );
// your code goes here
} finally {
// Don't forget to restore it !!!
thread.setContextClassLoader(originalClassLoader);
Be very cautious. If you fail to restore the original context class loader,
you will likely have to restart the server.
Hope this helps.
Regards,
Slava Imeshev
"Jon Sutula" <[email protected]> wrote in message news:[email protected]...
I am using WebLogic 8.1 and am trying to lookup the home interfacefor an EJB (_ejbRemote_)
from another EJB (_ejbCurrent_). They are deployed in seperate EARs.When I bundle
the home and remote interfaces for ejbRemote in the EAR file that
ejbCurrent
is deployed in, everything works fine. But I need to be able to configure
ejbRemote
at run time and my customers don't want to have to bundle their classesin my
EAR. So I invoke a custom classloader (of type java.net.URLClassLoader)that will
load the home and remote interface classes for ejbRemote from a configurable
location at runtime. This finds the classes no problem, and the InitialContext.lookup()
returns a stub, but I get a 'java.lang.ClassCastException: Cannot narrowremote
object' error when I call PortableRemoteObject.narrow(home, homeClass);
The code looks like:
// Assume EJBHomeStr = "com.foo.TestHome" in this case
// Load the home interface class. This works.
Class homeClass = urlClassLoader.loadClass(EJBHomeStr);
// Lookup the home interface. This works.
Object lookedUpHomeObject = initialContext.lookup(JNDIName);
// This fails.
Object homeObject = PortableRemoteObject.narrow(lookedUpHomeObject,homeClass);
And the weblogic error looks like
... ; nested exception is:
java.lang.ClassCastException: Cannot narrow remote object tocom.foo.TestHome
at weblogic.iiop.PortableRemoteObjectDelegateImpl.narrow(PortableRemoteO
bjectDelegateImpl.java:219)
at javax.rmi.PortableRemoteObject.narrow(PortableRemoteObject.java:134)
at ...[the rest is just my application code stack...]
When I log the ClassLoaders for the affected objects, using getClass().getClassLoader(),
I get:
<snippet from log follows>
getClass().getClassLoader(): weblogic.utils.classloaders.GenericClassLoader@667da1
finder:
weblogic.utils.classloaders.MultiClassFinder@db9199 annotation: myEJBApp@
homeClass.getName(): com.foo.TestHome classloader = java.net.URLClassLoader@4f1707
lookedUpHomeObject.getClass().getName(): com.foo.Test_EJB_kx82zy_HomeImpl_810_WLStub
classloader = weblogic.utils.classloaders.GenericClassLoader@667da1
finder: weblogic.utils.classloaders.MultiClassFinder@db9199 annotation:myEJBApp@
<end snippet from log>
So it appears that since the looked up Stub was loaded by the WebLogicclassloader
and the actual Home class was loaded by my URLClassLoader, the narrow()can't
reconcile the two. I have tried both rmic and the Weblogic appc commandto pre-generate
the stubs, which I put in the same JAR as my home and remote interfaceclasses
and load with my custom classloader. But the standard stub (generatedby either
rmic or appc) is named TestHomeStub.class and Weblogic is ignoringthose and
making a class with the name Test_EJB_kx82zy_HomeImpl_810_WLStub, asshown above.
I have also tried to put the remote interface classes and stubs inthe System
classpath using the -classpath option when I start WebLogic, but sameresult.
The question is, Is there a way in WebLogic to communicate with a remoteEJB in
a seperate EAR without bundling anything about that remote EAR in myEAR? Or is
there something I've missed? I need to keep my application J2EE compliant,meaning
I can't hardcode any AppServer-specific code in my application.
Thanks.