slf4j-log4j
· See http://www.slf4j.org/
Javadocs for the Log4jLoggerAdapter are available at
http://www.slf4j.org/api/org/slf4j/impl/Log4jLoggerAdapter.html
Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window slf4j-log4j13-1.0-beta9.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.