Actually this is due to the java.util.logging.SimpleFormatter used by the JDK by default which not only logs the LogRecord generated by any call to Logger#fine, Logger#severe, etc, but also an additional line with the date, source method, etc.
You can set up the a logHandler and specify a simpler Formatter, for example the "org.restlet.engine.log.AccessLogFormatter". You can have a look at the standard documentation or here.
Best regards, Thierry Boileau
I've configured logging.properties to only show WARNING level logs for Restlet and while that generally seems to work, I always get log entry for every request for the LogFilter istelf. Eg