Bugs item #697254, was opened at 2003-03-04 13:56
Message generated for change (Comment added) made by oravecz
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Category: JBossServer
Group: v3.2
Status: Closed
Resolution: Invalid
Priority: 5
Submitted By: Marcus Eriksson (marcuseriksson)
Assigned to: Scott M Stark (starksm)
Summary: ClassCastException when using EAR based scoping
Initial Comment:
I'm not sure if this behaviour is by design or a bug...
Two EARs with a bean in the first EAR calling a bean in
the second EAR.
Is this not possible if I use EAR based scoping?
I get a ClassCastException when I narrow the home of
the called bean:
Object o = ctx.lookup(jndiName);
TestBeanHome home = (TestBeanHome)
PortableRemoteObject.narrow(o,
TestBeanHome.class);
(JBoss 3.2.0RC2, J2SE1.4.1)
----------------------------------------------------------------------
Comment By: Jim Cook (oravecz)
Date: 2003-08-11 17:56
Message:
Logged In: YES
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I was going to post this on the forums (Pay Documentation),
since there is a TODO in the docs to expound upon this topic,
but the forums appear to be down.
Document Pass-By-Value semantics
Our project team has developed a number of general-purpose
EJBs, and these have evolved over time. Many of these EJBs
depend on shared class libraries that also evolve over time.
Now imagine that we have two general-purpose EJBs (called
EJB1 and EJB2) that are deploed into jBoss and utilized by our
application. EJB1 and EJB2 both use the library SHARED1.
Now, SHARED1 has evolved over time. In fact, EJB1 uses an
older version of SHARED1, while EJB2 uses a version that has
a few more methods available in it. Also, EJB2 has an ejb-ref
to EJB1, indicating that EJB2 depends on EJB1.
Given the current jBoss deployment scenario, we have three
options when it comes to the UnifiedClassloaders:
1. Deploy EJB1 and EJB2 in the same scope.
This is the default jBoss 3.2 behavior, and is easily achieved
by adding nothing extra to the deployment desciptors in the
EAR. It can also be achieved using the jboss-app.xml
descriptor specifiying the same name for the <loader-
repository> tag.
This approach will limit any duplicate class definitions (such as
all of the classes in SHARED1) to the first one encountered by
the classloader. If the SHARED1 (older version) in EJB1 gets
loaded first, then EJB2 will not have access to the newer
methods in its copy of SHARED1. This will manifest by
receiving the NoSuchMethodError exception.
2. Deploy EJB1 and EJB2 in separate scopes.
This is achieved by adding a META-INF/jboss-app.xml
descriptor to the ear files and specifying different values for
the <loader-repository> tag. With this approach, EJB1 and
EJB2 will use their own individual classloaders.
This approach gives each EJB access to their own SHARED1
library. However, EJB2 will eventually need to invoke a method
on EJB1, and when it goes to lookup the Home interface in
JNDI it can run into casting problems. Specifically, it attempts
to cast the JNDI embedded value (UCL1->EJB1Home) as EJB2-
>EJB1Home. This causes the ClassCastException since these
classes cannot be directly cast to each other.
3. Change the packaging of the EJB's HOME interfaces
By using scoped classloaders, it should be possible to move
the Home interfaces for EJB1 into the base UnifiedClassloader
(system classloader), but this seems mucho intrusive. This
can be further complicated when third-party EJBs are involved.
-------------
Apparently, the PortableRemoteObject.lookup behavior can be
changed to use Pass-By-Value semantics rather than the
default Pass-By-Reference approach, and this should solve
the only shortcoming in scenario #2 above.
Scott documented in a bug report (see reference) that pass-
by-value is activated by editing the client interceptors and
alluded to changing the way InitialContext is initiated.
Perhaps the change he mentions regarding InitialContext
lookups are necessary, but this would kill our portability and
seems way too intrusive.
Nevertheless, I have made changes to the interceptors and
the InitialContext in a small testcase without any affect. I still
continue to get ClassCastExceptions. Please provide the
complete docs on how to implement pass-by-value.
Questions:
1. Can the jBoss team provide complete documentation on
how to get scenario #2 above working on jBoss 3.2 RC2?
2. Does pass-by-value limit the application developer or
performance of the app server in any way? (other than the
cost of the lookup which I assume will now require some
serialization as opposed to a simple cast. at least we are in
the same VM.)
3. Does the pass-by-value behavior require all of the
InitialContext creation in our code to be affected? If so, this
seems like a really bad idea. Perhaps it can be made
dependent on a server config option?
----------------------------------------------------------------------
Comment By: Scott M Stark (starksm)
Date: 2003-03-05 07:54
Message:
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user_id=175228
Yes, this violates the point of scoping which is to isolate
the deployment classes. The TestBeanHome seen in ear1 will
not match the corresponding class bound into JNDI. You can
disable the call by reference mode which is causing the
class cast exception by creating a custom container
configuration that uses the ByValueInvokerInterceptor in the
client proxy. An example from the testsuite is shown below.
There still may be a problem with the JNDI lookup also using
a by reference semantic as well that needs to be turned off.
The only way to do this is to create an InitialContext with
the java.naming.provider.url=localhost:1099 property
defined. This causes the lookup to go through RMI and will
isolate the version of TestBeanHome bound into JNDI from the
one available in the second ear.
<?xml version="1.0" encoding="UTF-8"?>
<jboss>
<invoker-proxy-bindings>
<invoker-proxy-binding>
<name>by-value-stateless-rmi-invoker</name>
<invoker-mbean>jboss:service=invoker,type=jrmp</invoker-mbean>
<proxy-factory>org.jboss.proxy.ejb.ProxyFactory</proxy-factory>
<proxy-factory-config>
<client-interceptors>
<home>
<interceptor>org.jboss.proxy.ejb.HomeInterceptor</interceptor>
<interceptor>org.jboss.proxy.SecurityInterceptor</interceptor>
<interceptor>org.jboss.proxy.TransactionInterceptor</interceptor>
<interceptor>org.jboss.invocation.ByValueInvokerInterceptor</interceptor>
</home>
<bean>
<interceptor>org.jboss.proxy.ejb.StatelessSessionInterceptor</interceptor>
<interceptor>org.jboss.proxy.SecurityInterceptor</interceptor>
<interceptor>org.jboss.proxy.TransactionInterceptor</interceptor>
<interceptor>org.jboss.invocation.ByValueInvokerInterceptor</interceptor>
</bean>
</client-interceptors>
</proxy-factory-config>
</invoker-proxy-binding>
</invoker-proxy-bindings>
<enterprise-beans>
<session>
<ejb-name>ENCBean1</ejb-name>
<local-jndi-name>jbosstest/ejbs/local/ENCBean1</local-jndi-name>
</session>
<session>
<ejb-name>SecuredEJB</ejb-name>
<jndi-name>jbosstest/ejbs/SecuredEJB</jndi-name>
<configuration-name>Secure Stateless
SessionBean</configuration-name>
</session>
<session>
<ejb-name>UnsecuredEJB</ejb-name>
<jndi-name>jbosstest/ejbs/UnsecuredEJB</jndi-name>
<ejb-ref>
<ejb-ref-name>ejb/Session</ejb-ref-name>
<jndi-name>jbosstest/ejbs/SecuredEJB</jndi-name>
</ejb-ref>
</session>
<session>
<ejb-name>NotOptimizedEJB</ejb-name>
<jndi-name>jbosstest/ejbs/NotOptimizedEJB</jndi-name>
<invoker-bindings>
<invoker>
<invoker-proxy-binding-name>by-value-stateless-rmi-invoker</invoker-proxy-binding-name>
</invoker>
</invoker-bindings>
</session>
</enterprise-beans>
<container-configurations>
<container-configuration extends="Standard Stateless
SessionBean">
<container-name>Secure Stateless
SessionBean</container-name>
<security-domain>java:/jaas/other</security-domain>
</container-configuration>
</container-configurations>
</jboss>
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