Log5j is a lightweight and fast java logging library for Java versions 5 and above. It is very similar to log4j in style, but uses Java 5's varargs feature to allow any number of arguments to be passed to any logging method.
It also has tracef, debugf, infof, warnf, errorf, fatalf and logf methods, that will look very familiar to C developers. They allow more dynamic formatting of logging methods and are generally more efficient when messages are not logged.
The javadocs for log5j are available here.
Download log5j from the Sourceforge project page.