[slf4j-dev] jcl-over-slf4j module not building

Eric Crahen eric.crahen.lists at gmail.com
Wed Feb 21 00:01:29 CET 2007


The OSGi doesn't have Context ClassLoaders?

On 2/20/07, John E. Conlon <jconlon at verticon.com> wrote:
>
> Ceki Gülcü wrote:
> > John,
> >
> > Do you have a suggestion how we could avoid duplication of slf4j-api
> > classes in the various bindings? Can this be done using
> maven-bundle-plugin ?
> >
> At the moment I can think four approaches to removing the duplication of
> classes in the bindings that sit on 'Sally's application's classpath.
>
> 1. Keep the packages split across the api and binding projects, continue
> to rely on single classloader joining at runtime, and move back to a
> Require-Bundle approach for osgi support. We won't need the
> maven-bundle-plugin in the binding projects for this.
>
> 2. Remove the split packages by consolidating the packages into the api
> and binding jars, and use a 'service implementation' discovery similar
> that suggested by Eric in the "aufgeregt" thread :-) :
>
> http://www.qos.ch/pipermail/logback-user/2007-February/000129.html
>
> We should not depend on a sun impl for this so we would have to provide
> our own implementation, Boris has provided an example at:
>
> http://marc.theaimsgroup.com/?l=slf4j-dev&m=117157566417290&w=2
>
> While I have not experimented with his code, I do see one area that
> would require a change for it to work in an OSGi environment.
>
> public Object obtainFactory(ClassLoader cl) {
>         ILoggerFactory ret = null;
>         InputStream is = cl.getResourceAsStream(SERVICE_ID);
>
> Note: couldn't use a context classloader as it would not find the
> classes in an OSGi runtime. Sun's service api offers similar signatures.
>
> 3. Keep split packages and retain current way of combining api and
> bindings.  Remove OSGi decorations and maven-bundle-plugin from the five
> bindings projects.   Create five additional OSGi 'pom' projects that
> just wrap the api and bindings to create OSGi binding bundles.  These
> projects would only have a pom.xml (no code) and the artifacts they
> create would be the same bundles as we are now producing in the binding
> projects.  All other projects producing native jar/osgi bundles (like
> the adapters) would remain unchanged.
> (In this case Sally would not use the osgi-xxx-binding bundles.)
>
> 4. Convince Sally to run OSGi ;-)
>
> From an OSGi perspective I would rate them in order of functionality
> from higher to lower - 4, 3, 2, 1.
>
> kind regards,
> John
>
>
>
> > At 07:52 PM 2/19/2007, Ceki Gülcü wrote:
> >
> >
> >> At 08:25 PM 2/18/2007, John E. Conlon wrote:
> >>
> >>
> >>>> Assuming Maven 2 is used by all participants, without particular
> >>>> action by Sally, slf4j-api would be packaged in the final
> >>>> application along with a user-chosen binding, say slf4j-log4j12. In
> >>>> that case, we would have the contents of slf4j-api project
> duplicated,
> >>>> once in slf4j-api.jar and once in slf4j-log4j12.jar. It would most
> >>>> probably work as expected, but I don't think it's good practice to
> >>>> have class files duplicated.
> >>>>
> >>>>
> >>> I don't like this class duplication either, but AFAIK given the same
> >>> classloader this should not matter.  The same classloader will load
> >>> which ever it encounters first.  (Maybe I will eat these words
> latter?) ;-)
> >>>
> >> Hi John,
> >>
> >> The driving premise behind SLF4J is to reduce surprises. I think we
> >> should do things by the book and avoid duplication. Since SLF4J
> >> version 1.1, user's have been asked to have two jars, slfl4-api.jar in
> >> addition to a binding. In SLF4J 1.3, the general arrangement remains
> >> the same, except that slf4j-api is now self-sufficient as a
> >> compile-time dependency.
> >>
> >> I quite like this user-story. Alice and Bob expose slf4j-api as a
> >> transitive dependency, while Sally, the end-user, chooses to depend on
> >> a binding of her own selection.  We respond to Eric Crahen's initial
> >> request [1] without fundamentally changing how SLF4J works.
> >>
> >> I do not wish to hide behind backward-compatibility excuses. We
> >> finally have a nice and clear separation between slf4j-api and
> >> slf4j-binding. Let's keep it clean and simple even if it costs an
> >> extra jar on the class path.
> >>
> >> [1]
> >> http://www.qos.ch/pipermail/logback-user/2007-February/000129.html
> >>
> >>
> >>
> >>
> >>> a good weekend for you too,
> >>> John
> >>>
> >> --
> >> Ceki Gülcü
> >> Logback: The reliable, generic, fast and flexible logging framework for
> Java.
> >> http://logback.qos.ch
> >>
> >> _______________________________________________
> >> dev mailing list
> >> dev at slf4j.org
> >> http://www.slf4j.org/mailman/listinfo/dev
> >>
> >
> >
>
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-- 

- Eric
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