Log4j, configuring a Web App to use a relative path

public void contextInitialized(ServletContextEvent event) {
	ServletContext context = event.getServletContext();
	System.setProperty("rootPath", context.getRealPath("/"));
}

log4j.appender.file.File=${rootPath}WEB-INF/logs/MyLog.log

log4j.rootCategory=DEBUG,errorfile

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

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

log4j.rootCategory=DEBUG,errorfile

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

log4j.rootLogger=ERROR, stdout, rollingFile

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - <%m>%n

log4j.appender.rollingFile=org.apache.log4j.RollingFileAppender
log4j.appender.rollingFile.File=${myWebapp-instance-root}/WEB-INF/logs/application.log
log4j.appender.rollingFile.MaxFileSize=512KB
log4j.appender.rollingFile.MaxBackupIndex=10
log4j.appender.rollingFile.layout=org.apache.log4j.PatternLayout
log4j.appender.rollingFile.layout.ConversionPattern=%d %p [%c] - %m%n
log4j.appender.rollingFile.Encoding=UTF-8

<context-param>
  <param-name>log4jConfigLocation</param-name>
  <param-value>/WEB-INF/classes/log4j-myapp.properties</param-value>
</context-param>

<context-param>
  <param-name>webAppRootKey</param-name>
  <param-value>myWebapp-instance-root</param-value>
</context-param>

<listener>
  <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>