[slf4j-dev] Re quest for a log message processing hook.

[Robert Elliot]

Could you write a very lightweight implementation of SLF4J yourself  
that adds the listener hook and then forwards on to a wrapped "real"  
SLF4J implementation?  Effectively a decorator pattern for the real  
SLF4J logger.  This would also allow you to always return true from  
the isXXXXEnabled() methods, which would otherwise prevent you getting  
any logging messages inside blocks protected by them.

One issue I can see with this approach see is that you'd have binding  
problems - you'd need your decorator SLF4J implementation to be bound  
as "the" SLF4J implementation, and then have some other mechanism to  
bind the underlying SLF4J implementation you want to use for the  
actual logging.  Don't know if you could do anything clever with  
classloaders there on bootstrap?  Try and ensure that the apps general  
class loader loads the binding class from your decorator SLF4J  
implementation's jar, but inside your SL4J implementation you load any  
implementation of SLF4J on the classpath other than yours?  I confess  
my knowledge of classloaders isn't really up to answering that  
question without spiking it out myself.

Otherwise I have to say it seems more reasonable to set up the  
underlying logging system with the root logger set to debug and a  
special appender where you put your code, assuming you are in control  
of the configuration of the underlying logging system.


On 27 May 2009, at 15:38, ogradyjd wrote:

>
> I don't really want to say exactly what I'm working on right now for  
> various
> reasons, but I can tell you my needs.
>
> What I'm doing requires me to be able to receive all the messages  
> being
> logged, regardless of whether the underlying logging configuration  
> is set to
> log them or not.  For instance, if in the code I were to use slf4j  
> as the
> logger, and the underlying log system was Log4j, and the Log4j  
> configuration
> was set to "warn", I would still want to get copied on logging  
> messages for
> "info", "debug", etc...
>
> From there, the system I'm writing is going to process the logs in  
> it's own
> way, and then send them... somewhere else (he said, mysteriously).   
> It will
> be able to process the logs in a more dynamic way and pay attention  
> to the
> threads the log messages came from, so changing the configuration  
> files will
> be unnecessary.
>
> This is why I'm looking for a way to work with the abstraction layer  
> rather
> than the underlying log system.  What log messages get processed  
> will be
> completely independent of the log system configuration and will be
> instantaneous.  For the purposes of what I'm doing, consider the log
> configuration and output files normally generated as unreachable.
>
> Does that give you enough reasons why I'm looking for "listener" I  
> asked
> about?   No worries though. I understand your software has a  
> charter, so I
> will wrap the Logger and LoggerFactory implementations for now,  
> unless,
> given the above info, you have better ideas?
>
>
> Ceki Gulcu wrote:
>>
>>
>>
>> Thorbjoern Ravn Andersen wrote:
>>>
>>> Naturally.
>>>
>>> Often people who ask a question have gotten stuck on solving a  
>>> problem
>>> in a specific way, and ask about how to do the specific way.   
>>> Knowing
>>> about the underlying problem may allow an alternate approach which  
>>> may
>>> even happen to work better (if at all :) ).
>>
>> Indeed, the original problem might lend itself to different type of
>> solution.
>>
>>
>> -- 
>> Ceki Gülcü
>> Logback: The reliable, generic, fast and flexible logging framework  
>> for
>> Java.
>> http://logback.qos.ch
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>>
>>
>
> -- 
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