Multiple versions of a non-exported dependency

[cowwoc]

Well, this is unfortunate. As I stated earlier, I fail to see how 
depending on constant version numbers (not version ranges) fall under 
the scope of "version selection". Was this case considered/discussed in 
depth?

Not everyone is sold on version ranges (e.g. the vast majority of Maven 
artifacts I've seen depend on constant versions) and I think this would 
go a long way towards solving the original "classpath hell" problem.

Gili

On 2016-08-31 2:55 PM, Neil Bartlett [via jigsaw-dev] wrote:
> Gili,
>
> As Alex points out: your use-case can be supported in Java 9 but only 
> with the addition of custom ClassLoaders, or by using an existing 
> ClassLoader-based module system such as OSGi.
>
> The same is also true of Java 8, and Java 7, etc.
>
> Regards,
> Neil
>
>
> > On 31 Aug 2016, at 19:29, Alex Buckley <[hidden email] 
> </user/SendEmail.jtp?type=node&node=5713366&i=0>> wrote:
> >
> > On 8/31/2016 10:56 AM, cowwoc wrote:
> >> I recently became aware of the fact that the Jigsaw specification 
> declared
> >> "version-selection" as a non-goal. While I understand how we ended 
> up here,
> >> I am hoping that you were able to support the following (very common)
> >> use-case:
> >>
> >> * Module "HelloWorld" depends on modules "Guava" and "JSoup".
> >> * Module "Guava" depends on module slf4j version 1 (requires but 
> does not
> >> export it).
> >> * Module "JSoup" depends on module slf4j version 2 (requires but 
> does not
> >> export it).
> >> * slf4j version 2 and is not backwards-compatible with version 1.
> >>
> >> What happens at runtime? Will Jigsaw (out of the box, without 
> 3rd-party
> >> tools like Maven or OSGI) be smart enough to provide different 
> versions of
> >> slf4j to "Guava" and "JSoup"?
> >
> > (You mean Guava/JSoup requires slf4j version 1/2 and does not 
> "re-export" it a.k.a. 'requires public'.)
> >
> > This use case isn't possible on JDK 8 for JARs on the classpath, and 
> it's not supported on JDK 9 for modular JARs on the modulepath:
> >
> > - If you have two versions of a modular JAR slf4j.jar in different 
> directories on the modulepath, then the first one to be found will 
> dominate, and that's what will be resolved for both Guava and JSoup.
> >
> > - If you have two modular JARs slf4j_v1.jar and slf4j_v2.jar on the 
> modulepath, and Guava requires slf4j_v1 and JSoup requires slf4j_v2, 
> then launching 'java -m HelloWorld' will fail. The boot layer will 
> refuse to map the "same" packages from different slf4j_v* modules to 
> the application class loader.
> >
> > The use case _is_ supported on JDK 9 for modular JARs loaded into 
> custom loaders of custom layers. That is, the Java Platform Module 
> System is perfectly capable of supporting the use case -- please see 
> any of my "Jigsaw: Under The Hood" presentations. The use case just 
> isn't supported "out of the box" by the 'java' launcher for JARs on 
> the modulepath.
> >
> > Alex
>
>
>
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