[jboss-as7-dev] [Discuss] Making Shrinkwrap more module-classloader friendly

[Andrew Lee Rubinger]

Just a quick note while I'm bogged in TCK. :)

Find me on #jbosstesting for any integration questions or pull requests 
and I'll be happy to assist as I can.

For whichever implementation path you choose, let's get that into a SW 
extension module, built atop the existing API and implementation.  The 
static access and subsequent CL assumptions are in place to keep the 
user grammar slim and intuitive, but we'll absolutely make room for 
manual access in the right hooks if need be.

Let me know if we need some API changes to the core.

S,
ALR

On 12/10/2010 05:17 AM, David Bosschaert wrote:
> Hi all,
>
> I have been looking at getting Shrinkwrap to work in a module-based
> environment, like OSGi and JBoss Modules. I ran into issues with this
> basically because the interaction goes through the ShrinkWrap-API module
> and some static methods in there while the implementation requires that
> the ThreadContextClassLoader has visibility of Shrinkwrap-Impl module.
>
> In a classloader setting where all the SW jars are visible to the same
> classloader this works fine, but in a modules-based system these two
> modules would be loaded by two different classloaders so the only way to
> get the current approach work is to set the TCCL explicitly to the
> classloader that loads the ShrinkWrap-Impl module, which is a little
> awkward to do but also typically requires a dependency on a
> ShrinkWrap-Impl class which is ugly (IMHO), e.g:
>     ClassLoader oldCL = Thread.currentThread().getContextClassLoader();
>     try {
>       Thread.currentThread().setContextClassLoader(
>         JavaArchiveImpl.class.getClassloader()); // The impl class
>       Archive a = ShrinkWrap.create(...);
>     } finally {
>       Thread.currentThread().setContextClassLoader(oldCL);
>     }
>
> I can see two solutions to this.
>
> 1. The nicest one (IMHO) would be to let the impl module register a
> ShrinkWrap service (with MSC and/or OSGi) which handles all the TCCL
> details. The nice thing is that the user doesn't need to get into any SW
> implementation detail. Just use the service and it works - the API of
> the service would be similar to the ShrinkWrap class that's there today
> and defined in the API module. I guess the disadvantage would be that
> you need to obtain the service instance from the service registry, so
> you can't use a static API like ShrinkWrap.create().
>
> 2. An alternative could be to add additional static ShrinkWrap.create()
> (etc) methods that take a classloader as an argument. You would then
> still need to get hold of that classloader somehow, but at least you're
> freed of the TCCL setter wrapping code...
>
> Thoughts anyone?
>
> David
>
> BTW more context can be found in
> https://jira.jboss.org/browse/SHRINKWRAP-242 where I'm providing an
> initial proposal for #1 above to work in OSGi.
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