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
