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?
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
My suggestion is the log file should always be logged above the root context of the webApp, so in case we redeploy the webApp, we don't want to override the existing log files.