Struts uses
Apache commons logging, which is just a common API to get at many different underlying logging systems.
If you want to make the logging statements in the example work, just put log4j.jar in your WEB-INF/lib file, provide a log4j.properties file that defines appenders for the examples classes, and the logging statements will start outputting to those appenders. Apache Commons logging will sense the presence of log4j as your underlying logging system.