Apache Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x, and provides many of the improvements available in Logback while fixing some inherent problems in Logback's architecture.
The Log4j 2 User's Guide is available here or as a downloadable PDF.
Log4j 2.4 and greater requires Java 7, versions 2.0-alpha1 to 2.3 required Java 6. Some features require optional dependencies; the documentation for these features specifies the dependencies.
Apache Log4j 2 is distributed under the Apache License, version 2.0.
How to download Log4j, and how to use it from Maven, Ivy and Gradle.