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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