in spring/src/main/java/org/apache/logging/log4j/boot/spring/Log4jLoggingSystem.java [129:134]
protected void loadDefaults(final LoggingInitializationContext context, final LogFile file) {
final String configFileName = "classpath:META-INF/log4j/default/log4j2"
+ ((file == null) ? Strings.EMPTY : "-file")
+ ".xml";
loadConfiguration(context, configFileName, file);
}