A good explanation of commons-logging, slf4j, and log4j.

http://stackoverflow.com/questions/462566/logging-using-sl4j-jakarta-commons-logging-log4j-for-third-party-libraries-and

Remember to not confuse slf4j-xxxx.jar with xxxx-over-slf4j.jar. The former is for funneling to your desired logging framework (log4j, logback, etc), the latter is to replace the used logging framework. – Spencer K