We use [slf4j] which allows the underlying logging implementation to be statically bound at startup.
If you've got log4j.jar on your classpath you can use a log4j.properties file to configure the logging levels. See the log4j.properties example for the kind of thing you'll need.
e.g. adding the following to your log4j.properties will enable tracing of ActiveMQ code:
If you are new to log4j please see the log4j manual