[xwiki-users] Configuration to use log4j instead of logback for xwiki 3.1 and beyond?

At http://platform.xwiki.org/xwiki/bin/view/AdminGuide/Logging, it is stated that By default XWiki is configured so that SLF4J uses Logback. XWiki's Logback configuration is located in the WEB-INF/classes/logback.xml file for For XWiki 3.1 and beyond. But if user want to use log4j instaed of logback, where it needs to be configured. I did not find any property related to that in xwiki.cfg or xwiki.properties.What i tried deleting the logback.xml and putting my log4j.properties instaed. But xwiki does not pick log4j.properties. As per my understanding, xwiki is using SLF4J, there should be hook somewhere where we should be able to change to log4j insteadd of logback.