I have a question on the best way to handle configuring log4j when multiple
sub-systems/components each are using log4j. For example, if you use Struts
and Cactus in addition to your own code then there are 3 different users of
log4j that may require specific things to be setup at configuration time,
for example custom categories/category factories.
My thinking is that in each sub-system configuration, you only address
things that are specific to that particular sub-system,. That is, you
follow a naming convention to minimize name clashes, such as
SubSystem1_ConsoleAppender. You only set priorities and appenders for the
specific sub-system categories, e.g.
log4j.category.org.subsystem1=DEBUG,SubSystem1_ConsoleAppender and never
set global things like rootCategory, ending up with a structure along the
following lines :
SubSystem1
SubSystem1_Log4jConfig.xml (if custom categories are used) OR
SubSystem1_Log4jConfig.properties
SubSystem2
SubSystem2_Log4jConfig.properties
... etc
However, if you only address things that are specific to a particular
sub-system in the configuration file for that sub-system (which is probably
a good thing), how do you handle the case where the sub-system is used in
isolation and you want to setup some global defaults, such as rootCategory
logging ? One possible solution would be to use the command line
-Dlog4j.configuration= method or you can initialize these global things
from your own code directly or via a configuration file loaded by your own
code or even better would be letting the default log4j initialization take
care of that issue.
One problem with this approach that springs to mind is those people that
want all the log4j configuration in one place and not spread over multiple
files. How would you tell the sub-system not to do it's initialization? If
the sub-system used custom categories would a reasonable approach be to
check to see if one of those categories was already defined in the list
returned by Category.getCurrentCategories() and then only initialize if it
wasn't yet defined?
On another tack, it appears the only way to handle custom categories in a
safe, extensible manner is to use the DOMConfigurator, is that correct ?
TIA
Robert
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