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Re: [equinox-dev] OSGi & RMI 
Hi Patrick,

Looks like BeanRegistrar.lookup constructs a proxy that implements
IExampleRemote, but probably uses a different classloader during its
construction - this would explain why it can't be cast to the local type.

If you have access to the lookup code, try to see what classloader it
uses - ie. getClassLoader() on an existing type (from either the client
or the provider bundle) or the thread context classloader (TCCL).

If the proxy only needs access to the client types then you just need
to use the client classloader - either by getting the lookup method to
use getClassLoader on one the parameters passed in from the client,
or by setting the TCCL to the right classloader before the lookup call
(and resetting it afterwards).

If the proxy needs access to both client and provider types then one
solution is to use a custom classloader to 'bridge' the two hierarchies.
Basically this bridge classloader would know about client and provider
classloaders and delegates to the right one according to the package
name (or delegate one way then delegates the other way on failure).

Alternatively you could try Dynamic-ImportPackage: * in the provider
bundle, which would allow it to find the right client type instance, but
this forces you to expose implementation types in your client, and
makes it harder to replace and re-wire packages.

Another option is using Eclipse-BuddyPolicy to bridge across bundles
but this is specific to Equinox and isn't supported on other frameworks.

For some extra info on this see:

 http://www.eclipsezone.com/articles/eclipse-vms
 http://www2.osgi.org/pipermail/jsr-291-eg/2006-August/000169.html
 https://bugs.eclipse.org/bugs/show_bug.cgi?id=87775

hope this helps :)

( if not, a zipfile of the code would be useful, as Edward suggested )

On 12/05/07, Patrick Bakker <patrick@xxxxxxxxxxxx> wrote:

Hi,
I'm experimenting with the best way to modularize an application using Swing
to communicate to stateless session beans. I'm using Java SE 5 + JBoss
4.2.0.CR2 + Eclipse 3.2.2.
I know its some kind of classloader/isolation issue with OSGi/RMI because I
can construct a simple Java application that works fine.

Suppose I have 5 bundles (I'm using Eclipse bundles rather than OSGi but I'm
using Swing not SWT) & their important classes:
example.app
example.registrar.bean
  BeanRegistrar (singleton)
  jndi.properties
example.client
example.clientserver
  IExample
  IExampleRemote
example.server
  ExampleBean

For JBoss I use an ant script to create jar from the packages in
example.clientserver and example.server to create example.server.jar which I
drop in the deploy directory:

@Stateless
@RemoteBinding(IExampleRemote.DEFAULT_JNDI_NAME)
public class ExampleBean implements IExample, IExampleRemote
{
   public void doSomething()
  {
    System.out.println("hello");
  }
}

public interface IExample
{
  public void doSomething();
}

@Remote
public interface IExampleRemote extends IExample
{}

For the client I have everything packaged as individual bundles. When
example.client needs a bean it starts another thread which calls
BeanRegistrar.lookup(String jndiName) to get a reference to a remote bean.

public class Task extends Thread
{
  boolean inSwing;
  TaskCallback callback;

  public void Task(TaskCallback callback)
  {
    this.callback = callback;
    inSwing = false;
  }

   public void run()
  {
    if (inSwing)
    {
      callback.taskComplete();
    }
    else
    {
      IExampleRemote example = (IExampleRemote)
BeanRegistrar.lookup(IExampleRemote.DEFAULT_JNDI_NAME );
      example.doSomething();

      inSwing = true;
      SwingUtilities.invokeLater(this);
    }
  }
}

If I collapse this entire example down to a simple Java application instead
of bundles it works fine.
If I run it as an Eclispe RCP, I get:

java.lang.ClassCastException: $Proxy0 cannot be cast to
example.clientserver.IExampleRemote
    at example.client.Task.run(Task.java:xx) <-- stops at the line with
BeanRegistrar.lookup

I've googled around extensively and OSGi/RMI issues come up in several
places but the closest anybody gets to answering anything is to hint that
this may be problematic and the conversation ends just before anybody says
anything useful. A few other documents mention the Eclipse Buddy policy
extension. I've experimented with it but have not had any success yet. Also,
I'm not sure exactly what I'm trying to do so I'm basically just guessing at
possible combinations.

I am running the program under the default Java security manager with the
following permissive policy:
grant
{
    permission java.security.AllPermission;
};

I do that by supplying VM arguments to the run program option in Eclipse:
-Djava.security.manager
-Djava.security.policy="/Configuration/security.conf"
-Djava.security.auth.login.config="/Configuration/jaas.conf"

Can anybody help me get to the bottom of this?


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--
Cheers, Stuart

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