[slf4j-user] Class path contains multiple SLF4J bindings: gossip and slf4j-log4j12

[Ceki Gulcu]

Hi Nils,

Without detailed info it is hard to tell, but as a general rule,
embedded components should not attempt to configure logging. See
[1]. By analogy, they should also not include an slf4j-binding in
their distribution.

As of SLF4J v1.6.0, in the absence of a binding, slf4j will default to
an NOP implementation. This further restricts the number of cases
where a library would need to include a binding in its
distribution. See [2].

Given the above, it looks like both GMaven and Magnolia CMS could be
alerted about the conflict you are experiencing.

[1] http://slf4j.org/faq.html#configure_logging
[2] http://slf4j.org/codes.html#StaticLoggerBinder


On 07.10.2010 18:03, Nils Breunese wrote:
> Robert Elliot wrote:
>
> Thanks for the fast response!
>
>> Gossip and log4J are both logging systems.
>
> I found that it is a 'plugin for SLF4J', but I didn't know that it was a logging system in its own right.
>
>> The big question is why your modules think they need to specify a logging system; in the case of gmaven I would guess because you are using it embedded but it can also run stand-alone.
>
> GMaven is embedded in our build to generate Java stubs in a mixed Java/Groovy submodule. gmaven-runtime-1.7:1.3 brings in gmaven-runtime-support:1.3, which brings in gshell-io:2.0, which brings in gossip:1.0.
>
>> In the case of the other module I would guess that it's a legacy one, and you should be using log4j-over-slf4j to redirect log4j to it (unless you actually want to use log4j).
>
> The other module uses Magnolia CMS, which via a couple of links brings in both slf4j-log4j12 and jcl-over-slf4j according to mvn dependency:tree.
>
>> You could try excluding gossip and log4j explicitly (by giving them "provided" scope) and choosing your own logging implementation such as logback.
>>
>> If you do not it will be an arbitrary consequence of classloading order as to which logging system (gossip of log4j) ends up handling any log calls to SLF4J.
>
> Ok thanks, we'll look into this.
>
> Is there anything which should be reported as a bug to either GMaven or Magnolia CMS, or is this just our combination of the two?
>
> Nils.
> ------------------------------------------------------------------------
>   VPRO
>   phone:  +31(0)356712911
>   e-mail: info at vpro.nl
>   web:    www.vpro.nl
> ------------------------------------------------------------------------