Classloading issue using spring remoting. Was: Wait for SMX4 to use RMI?

[Erhard Siegl <Er...@at.unisys.com>]

bsnyder wrote:
> 
> 
> We can build a binding component for making RMI calls in ServiceMix 3
> pretty easily because Spring already provides proxy objects to handle
> this:
> 
> http://static.springframework.org/spring/docs/2.0.x/api/org/springframework/remoting/rmi/package-summary.html
> 
> Other APIs from the Spring Framework have already been reused in
> ServiceMIx 3 for other components. Reusing more APIs and building on
> them where needed is the easiest way to achieve this and shouldn't be
> too difficult to do. And I'm happy to help so that we can continue to
> add new components to expand ServiceMix's ability to interoperate with
> more and more technologies.
> 
> Bruce
> -- 
> perl -e 'print
> unpack("u30","D0G)U8V4\@4VYY9&5R\"F)R=6-E+G-N>61E<D\!G;6%I;\"YC;VT*"
> );'
> 
> 
> 

I try to write a BC using
org.springframework.remoting.rmi.RmiServiceExporter in order to use RMI to
access ServiceMix. The SU should implement the service and forwards the
message to the NMR. The ConsumerEndpoint should start the RMI-Listener using
Spring. Implementing this, I experienced some classloading-problems. After
some time of sarching and reading, the cause seems to be the following:

The Service Unit is started by the SU-classloader (xbean configuration). It
uses Spring classes (RmiServiceExporter), that are loaded by the container
class loader. The RmiServiceExporter starts a listener with the container
classloader. For this it needs aopalliance-1.0.jar, which is not in the
classpath of the container classloader and a ClassNotFoundException occurs.
This can be fixed by putting the jar to lib/optional. This starts the
RMI-listener.

But when an object comes in the listener has to unmarshal it and needs the
class. Again it uses the container classloader and a ClassNotFoundException
occurs. Putting these specific classes into lib/optional works, but it isn't
something, I'd like to do.

To fix this, the Spring-classes have to be loaded from the SU-classloader,
but I couldn't figure out how to do this. According to the postings here,
this seems to be a common problem, that occurs when someone is using Spring
in a SU or BC.

I tried to put the spring.jar into the SU. This doesn't help, since the
parent-classloader is asked first to load the class. I put <classpath
inverse="true" /> into the configuration, but ran into other problems and
the component didn't start. 

Since the goal is to prevent the parent classloader to load the
spring-classes, the <hidden> xxx </hidden> in the classpath-configuration
might help, but I still have to try that. Any other ideas?
(See also http://docs.huihoo.com/apache/servicemix/classloaders.html )

Erhard

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