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From Michał Kłeczek <michal.klec...@xpro.biz>
Subject Re: River-436 - need some explanation of preferred class provider
Date Tue, 04 Mar 2014 05:38:04 GMT
1. The problem is there is no such thing as "the service interface". It is
context dependent. What is "the service interface" for service browser?

2. In this particular case Util interface is an implementation detail of
WrapperProxy. It is Wrapper interface the client is interested in. So I
would say it should be preferred in WrapperProxy codebase.

3. Even if Util is not preferred in WrapperProxy codebase we still have
ClassCastException if the client does not have Util in its classpath. Why
should it? it is interested in Wrapper not in Util. So either
a. We always get ClassCastException if Util is preferred in WrapperProxy
codebase, or
b. We get ClassCastException anyway if a client does not have Util in its
classpath.
Let's say I want to register RemoteEventListener that wraps a Javaspace
proxy to write events in a space. Does that mean the service "event source"
has to be aware of Javaspace interface??? That would be absurd...

It all does not have anything to do with codebase services.

Thanks,
Michal
4 mar 2014 00:09 "Peter" <jini@zeus.net.au> napisał(a):

> The Util interface should not be preferred.  Implementations of Util can
> be preferred but not Util itself.
>
> Services need a common api that all implementations and clients can use to
> interract, even if this is a kind of codebase service.
>
> Modifying an interface is generally considered bad practise but now Java 8
> makes it possible to add default methods for added functionality, that line
> blurs somewhat.  What can you do if an earlier interface is loaded by a
> parent ClassLoader and you need a later version, make it preferred?
>
> My thoughts are that interfaces should never be preferred and all classes
> defined in their methods shouldn't be preferred either.
>
> It would be relatively easy to write a new implementation that ensures
> that interfaces are loaded into their own ProtectionDomain in a parent
> ClassLoader.  But that would be confusing as dynamic policy grants are made
> to ClassLoader's not ProtectionDomains.
>
> But using ProtectionDomains in this manner, preserves security, ensures
> maximum visibility and avoids codebase annotation loss, if we ask the
> ProtectionDomain for the annotation, instead of the ClassLoader.  But this
> is not how we do things presently.
>
> Cheers,
>
> Peter.
>
> ----- Original message -----
> > But it will also be loaded by WrapperProxy ClassLoader, since it is
> > preferred there. So it will end up with ClassCastException, right?
> >
> > Regards,
> > Michal
> >
> > If Util is installed locally, it will only be loaded by the application
> > ClassLoader, since it isn't preferred.
> >
> > Peter.
> >
> > ----- Original message -----
> > > Folks,
> > > while woking on the River-436 patch proposal I've came across the
> > > scenario that I am not sure how to handle:
> > >
> > > Utility service:
> > > //inteface is NOT preferred
> > > interface Util {...}
> > > //class IS preferred
> > > class UtilProxy implements Util {}
> > >
> > > Wrapper service:
> > > //NOT preferred
> > > interface Wrapper {}
> > > //preferred
> > > class WrapperProxy implements Serializable{
> > > //initialized with Util impl from a lookup service
> > > private Util util;
> > > }
> > >
> > > Wrapper service codebase includes Util interface but it is _preferred_.
> > >
> > > Would deserialization of WrapperProxy end with ClassCastException?
> > > From what I understand UtilProxy is annotated with its codebase. When
> > > deserializing UtilProxy a ClassLoader is going to be created with
> > > parent set to TCCL. It means Util interface is going to be loaded
> > > twice by two ClassLoaders - one for WrapperProxy codebase and another
> > > for UtilProxy codebase.
> > >
> > > Am I correct?
> > > And if so: is it desired behavior?
> > >
> > > Regards,
> > >
> > > --
> > > Michał Kłeczek
> > > XPro Quality Matters
> > > http://www.xpro.biz
> > >
>
>

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