I got the following wanrning messages:
log4j:WARN No appenders could be found for logger (org.apache.fop.render.RendererFactory)
log4j:WARN Please initialize the log4j system properly.

Anyone knows why?
Thanks.
Tuan
content of  log4j.pdf.properties:

# FO to PDF logging configuration
log4j.rootLogger=ERROR, A1
log4j.appender.A1=org.apache.log4j.FileAppender
log4j.appender.A1.File=debug_pdf.txt
log4j.appender.A1.Append=false
log4j.appender.A1.layout=org.apache.log4j.PatternLayout


contents of log4j.xsl.properties:

# XML to FO logging configuration
log4j.rootLogger=ERROR, A1
log4j.appender.A1=org.apache.log4j.FileAppender
log4j.appender.A1.File=debug_xsl.txt
log4j.appender.A1.Append=false
log4j.appender.A1.layout=org.apache.log4j.PatternLayout