Log4j, configuring a Web App to use a relative path

Question

I have a java webapp that has to be deployed on either Win or Linux machines. I now want to add log4j for logging and I'd like to use a relative path for the log file as I don't want to change the file path on every deployment. The container will most likely be Tomcat but not necessarily.

What's the best way of doing this?

Answer 1

Tomcat sets a catalina.home system property. You can use this in your log4j properties file. Something like this:

log4j.rootCategory=DEBUG,errorfile  log4j.appender.errorfile.File=${catalina.home}/logs/LogFilename.log 

On Debian (including Ubuntu), ${catalina.home} will not work because that points at /usr/share/tomcat6 which has no link to /var/log/tomcat6. Here just use ${catalina.base}.

If your using another container, try to find a similar system property, or define your own. Setting the system property will vary by platform, and container. But for Tomcat on Linux/Unix I would create a setenv.sh in the CATALINA_HOME/bin directory. It would contain:

export JAVA_OPTS="-Dcustom.logging.root=/var/log/webapps" 

Then your log4j.properties would be:

log4j.rootCategory=DEBUG,errorfile  log4j.appender.errorfile.File=${custom.logging.root}/LogFilename.log