The Log4j 2 implementation provides the functional components of the logging system. Users are free to create their own plugins and include them in the logging configuration.
As of version 2.4, Log4j 2 requires Java 7. Versions 2.3 and earlier require Java 6. Some features may require optional dependencies. These dependencies are specified in the documentation for those features.
Some Log4j features require external dependencies. See the Dependency Tree for the exact list of JAR files needed for these features.