Should ClassLoader::getResouces return the same resource twice?

[Thiago Henrique Hupner]

Yes, the parent loader locates two resources and it is used in the
defineModulesWithOneLoader.

So the behavior is the following:
module-a.jar -> META-INF/web-fragment.xml
module-b.jar -> META-INF/web-fragment.xml

Creating a URLClassloader with these two jars and calling the getResources,
it returns two URLs.

If then I create a module for each jar, the contents of each module will be
the same as the content
found by the URLClassloader.
Using that classloader as the parent in the defineModulesWithOneLoader
gives the following behavior:

Calling getResources with the loader created by the ModuleLayer,
it will search the resources in all the modules of that layer (module.a and
module.b),
and then delegate to the parent (URLClassloader), which will find the same
resources,
thus, doubling the results.

Now describing it make clear to me that is something not easy to fix,
so by now, I worked around it by creating a ModuleReader that only
find the ".class" files in the module and the other resources will be
available by the parent,
however, I don't know if this solution is the best.


Em sáb., 2 de jan. de 2021 às 14:51, Alan Bateman <Alan.Bateman at oracle.com>
escreveu:

> On 02/01/2021 12:59, Thiago Henrique Hupner wrote:
> > I guess a little context can make more things clear:
> > The servlet spec requires that all jars from WEB-INF/lib
> > be available to the same classloader.
> > The resource, in particular, is "META-INF/web-fragment.xml"
> > Each jar can contain its own. So, using getResources make sense
> > in order of parsing each. However, what is happening is if I have two
> JARs
> > each with its own META-INF/web-fragment.xml, using the ModuleReader
> > it is returning four resources, so it parses more than it should and
> > it fails
> > to parse the same resource twice.
> >
> Which parent class loader are you specifying to
> defineModulesWithOneLoader? It it possible that it locates the resource
> in the two JAR files?
>
> -Alan
>