It's almost 2 months since you wrote this, so I suppose I'm too late.
Nevertheless, I'll send you a piece of code I found in "professional Apache Tomcat", from Wrox.

You need an initialisation servlet in which you write :
String path = getServletContext().getRealPath("/");
String properties = path + getInitParameter("properties");
PropertyConfigurator.configure(properties);

Via getServletContext you get the full path of the servlet. You add to this the name of the properties-file which you have defined in your web.xml like this :

org.brukkerlin.servlets.EddiLog4jServlet
org.brukkerlin.servlets.EddiLog4jServlet

properties
WEB-INFclasseslog4j.properties

1


And then you need a log4j.properties file, in which you write :

# definitie van simple logger
# level van de logger is DEBUG (dus op één na hoogste; hoogste = ALL)
log4j.logger.eddi.simple=DEBUG, simple

#definitie van de appender : bepaalt naar waar de logging geschreven wordt
log4j.appender.simple=org.apache.log4j.FileAppender
log4j.appender.simple.File=C:Program FilesApache GroupTomcat 4.1logseddi.log

#bepalen van de layout
log4j.appender.simple.layout=org.apache.log4j.SimpleLayout