config log4j via slf4j

we have a standalone java project using log4j for logging,and we don't config log4j via the classpath configuration. we config it in my code as bellow:

String configLocation = System.getProperty("S_HOME") + File.separator +"config"+ File.separator +"xxxLog.properties";PropertyConfigurator.configure(configLocation)

but if we move to slf4j,how can I config log4j via slf4j?

THKS