If you use JBoss version shipped with log4j, you should see logs printing on JBoss console. If your JBoss doesn't use log4j you have to configure properly the logger, in other words you have to add appenders to this logger.
You may also try to get logger in this way:
Logger logger = Logger.getLogger("MyLogger");
or even better
Logger logger = Logger.getLogger(YourClassName.getClass());
where YourClassName is the name of the class where you instantiate logger, which is most recomended by folks that wrote log4j.
Hope this helped