log4j 2 configuration: appenderRef.xyz.ref?

Question

From https://logging.apache.org/log4j/2.x/manual/configuration.html:

appender.rolling.type = RollingFile
appender.rolling.name = RollingFile

   ...

logger.rolling.name = org.apache.logging.log4j.core.appender.rolling
logger.rolling.level = debug
logger.rolling.additivity = false
logger.rolling.appenderRefs = rolling
logger.rolling.appenderRef.rolling.ref = RollingFile

What does the last line do? I get that logger.rolling.appenderRefs = rolling causes the rolling logger to point towards the rolling appender, but I don't understand the last line.

Answer 1

This

logger.rolling.appenderRefs = rolling

first declares a set of appender references by name. Here, it declares one named rolling. This rolling is unrelated to the rolling in

appenders = console, rolling, list

This

logger.rolling.appenderRef.rolling.ref = RollingFile

uses the previously declared name to refer to the appender reference. The .ref then connects that appender reference with the appender named RollingFile.