[slf4j-user] Reconfigure during runtime

[Ceki Gülcü]

On 17/02/2010 9:20 AM, Per Lindberg wrote:
> Ceki Gülcü wrote:

>> SLF4J loggers do not have setters or getters for levels. You would
>> need to use the log4j API directly to set logger levels.
>
> I hav tried just that, using the code snippet above.
> It calls log4j directly:
>
> org.apache.log4j.Logger root = org.apache.log4j.Logger.getRootLogger();
> root.setLevel(org.apache.log4j.Level.DEBUG);
>
> No luck.

By default, log4j assigns the DEBUG level to the root logger. Thus,
the code above is idempotent with respect to a default configuration.
Just to be sure, when you say "no luck", do you mean that the code has
no affect (which is normal) or do you mean that it doesn't compile or
throws an exception? If so, you have probably placed
log4j-over-slf4j.jar on your class path.

Which jar files do you have on your class path?

> (I had then plans to do it more specifically by passing request
> parameters with specific log level and class path:
>
> org.apache.log4j.Logger logger =
> org.apache.log4j.Logger.getLogger(classPath);
> org.apache.log4j.Level level = org.apache.log4j.Level.toLevel(logLevel);
> logger.setLevel(level);
>
> Since I import slf4j, I of course must specify the full package
> qualification for the log4j calls.)

If in the particular class where the log4j configuration calls are made, you do 
not invoke SLF4J, you could avoid the SLF4J imports but import log4j classes 
instead. However, if you are using both, you need to refer to the class of the 
non-imported package in fully qualified form.

>> This would tie your code to log4j.
>
> Ah, you mean that I would have to throw out slf4j,
> and use log4j directly for logging?

No, that's not what I meant. SLF4J gives you the ability to easily
switch logging frameworks. If you use SLF4J as your logging API, you
can switch from one logging framework, say from log4j to j.u.l, or
from log4j to logback, within minutes, unless your code makes direct
calls to the underlying logging framework, log4j in your case. The
more direct calls you make to the underlying logging framework, the
harder it is to switch.

>> However, it would do so at one single point
>> instead of throughout your application.
>
> Sorry, I didn't understand that.

I hope the previous paragraph explains it a bit better.