Since Spring Boot 1.3 you have a better way of getting spring properties into your logback-spring.xml configuration:
Now you can just add a “springProperty” element.
<springProperty name="destination" source="my.loggger.extradest"/>
<appender name="FILE" class="ch.qos.logback.core.FileAppender">
<file>${destination}</file>
...
</file>
</appender>
https://github.com/spring-projects/spring-boot/commit/055ace37f006120b0006956b03c7f358d5f3729f
edit: thanks to Anders
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