Investigate and find out which logging package it's using. It's probably one of Jakarta Commons Logging, Apache Log4j, or Sun's. Once you figure out which one it's using then your next step is to figure out how to configure that logging package.
http://jakarta.apache.org/commons/logging/
http://logging.apache.org/log4j/docs/
http://java.sun.com/j2se/1.5.0/docs/guide/logging/index.html