risolto..
codice:
# Sample properties to initialise log4j
#log4j.rootCategory=debug, stdout, R

log4j.rootLogger=OFF

log4j.category.miopakage.sottopakage=ALL, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout

# Pattern to output the caller's file name and line number.
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

log4j.appender.R=org.apache.log4j.RollingFileAppender
log4j.appender.R.File=logtags.log

log4j.appender.R.MaxFileSize=100KB
# Keep one backup file
log4j.appender.R.MaxBackupIndex=2

log4j.appender.R.layout=org.apache.log4j.PatternLayout
log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n
così facendo si blocca l'output su tutto e si tiene aperto solo per le nostre classi (miopakage.sottopakage)

poi nella servlet si richiama Logger logger = Logger.getLogger(this.getClass().getName());