Spring boot is using logback as its logging system and you can configure logging level via application.yaml property file but if you need more fine tunning, a logging configuration (normally xml) would be required. This file is normally put into your resources folder. Normally, we just call it logback.xml file as logback framework will automatically find this file and load the content. But in Spring, in order to initalize the context, Spring recommends a special requirement on the namming convention:

The logging file should be suffixed with -spring.xml. E.g logback-spring.xml

Only in this way, Spring is intructed to take control of the logging initialization. This behaviour has been documented in spring’s doc page.