The important detail for me, is that ClassLoader per module, with the current Class resolution scheme (this ClassLoader and whatever I can find in the parent), provides a lot of issues. The “custom ClassLoaders” or “containers like OSGi” remarks point at the “us and them” attitude that is pretty prevalent in this conversation. The majority of developers are looking for a module system that is not an “us or them” proposition. These “all or nothing” compromises are what create the “hell” that dominates conversations here. What we all want to be able to do, is write software once, target it to “THE Java platform”, and be done.
What Sun and now Oracle are continuing to do, is create more stuff that is nothing like what everyone else is doing with modularity and instead create something that is orthogonal to most peoples problem spaces and in the end creates tremendously more “work” for nothing more than compatibility with the new “JVM” environment. The real goal here needs to be making all of the other module and container systems obsolete. Those systems should “want” to provide support for the awesome, new module system that will make in unnecessary for them to roll their own details any longer. Yes, that is a long road and a tall measure for success. But frankly, even the lack of any visibility of the style of modules that Netbeans has used for decades makes it clear that this groups view at Oracle is extremely narrow and perhaps even more uninformed about what the community actually needs. Gregg > On Sep 1, 2016, at 7:29 AM, David M. Lloyd <david.ll...@redhat.com> wrote: > > It seems like there is no good reason why the application modules aren't > loaded with classloader-per-module now. The platform stuff could all be in > one, but the application stuff? Problems like this are going to come up a > lot otherwise; let's consider making that change. > > On 08/31/2016 07:45 PM, Neil Bartlett wrote: >> Remi, >> >> Actually I don’t think that statically linking will work. This would produce >> modules that have overlapping private (non-exported) packages, and such >> modules also cannot be used in Java 9 on the modulepath. >> >> I tested this in build 9-ea+126-jigsaw-nightly-h5280-20160713 by creating >> two modules both containing a private package org.example.util. The >> following exception resulted: >> java.lang.reflect.LayerInstantiationException: Package org.example.util in >> both module a and module b. >> >> Again this could be “solved” by using custom ClassLoaders or a >> ClassLoader-based module system like OSGi on Java 9. >> >> Neil >> >> >> >>> On 31 Aug 2016, at 20:28, Remi Forax <fo...@univ-mlv.fr> wrote: >>> >>> The other solution is to statically link the right version of slf4j inside >>> guava and jsoup. >>> A tool like jarjar can be updated to merge two modular jars (merge two >>> module-info). >>> >>> cheers, >>> Rémi >>> >>> ----- Mail original ----- >>>> De: "Neil Bartlett" <njbartl...@gmail.com> >>>> À: cow...@bbs.darktech.org, "Alex Buckley" <alex.buck...@oracle.com> >>>> Cc: "ZML-OpenJDK-Jigsaw-Developers" <jigsaw-dev@openjdk.java.net> >>>> Envoyé: Mercredi 31 Août 2016 20:54:44 >>>> Objet: Re: Multiple versions of a non-exported dependency >>> >>>> 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 <alex.buck...@oracle.com> 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 >> > > -- > - DML
