SLF4J
The Simple Logging Facade for Java (SLF4J) provides a Java logging API by means of a simple facade pattern. The underlying logging backend is determined at deployment time and includes java.util.logging, log4j and logback.
The separation of the client API from the logging backend reduces the coupling between an application and any particular logging framework. This can make it easier to integrate with existing or third-party code or to deliver code into other projects that have already made a choice of logging backend.
SLF4J was created by Ceki Gülcü as an enhancement over the already-successful log4j framework. It improves on log4j by addressing a few criticism of log4j relating to performance.
SLF4J was also created partly in response to certain criticisms of the Jakarta Commons Logging framework.