If I update my project from Log4J 2.24.1 to 2.25.0 (no other changes), I no longer get logging output.
Spring Boot 3.5.1, gradlew :subprojects:app:run.
Diff: https://github.com/sdkotlin/sd-kotlin-spring-talks/commit/b15de4858a0c10ab9c267489b1b5a98cf1a9e10d.
Log4J 2.24.1 https://github.com/sdkotlin/sd-kotlin-spring-talks/tree/8d40d0c54e700adbc7c7609eb2b04a16223869ab
> Task :subprojects:app:run
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v3.5.1)
2025-06-19T10:14:37.901-07:00 INFO 65736 --- [ main] o.s.s.SpringBootAppKt : Starting SpringBootAppKt using Java 21.0.7 with PID 65736 (/Users/ianbrandt/Development/SDKotlin/sd-kotlin-spring-talks/subprojects/app/build/classes/kotlin/main started by ianbrandt in /Users/ianbrandt/Development/SDKotlin/sd-kotlin-spring-talks/subprojects/app)
2025-06-19T10:14:37.903-07:00 INFO 65736 --- [ main] o.s.s.SpringBootAppKt : No active profile set, falling back to 1 default profile: "default"
2025-06-19T10:14:38.107-07:00 INFO 65736 --- [ main] k.r.KClass : Config path: /Users/ianbrandt/Development/SDKotlin/sd-kotlin-spring-talks/subprojects/app/config
2025-06-19T10:14:38.107-07:00 INFO 65736 --- [atcher-worker-1] k.r.KClass : The current time is 2025-06-19T17:14:38.107189Z
2025-06-19T10:14:38.107-07:00 INFO 65736 --- [ main] k.r.KClass : Log path: /Users/ianbrandt/Development/SDKotlin/sd-kotlin-spring-talks/subprojects/app/logs
You've been scanned.
2025-06-19T10:14:38.128-07:00 INFO 65736 --- [ main] o.s.s.SpringBootAppKt : Started SpringBootAppKt in 0.395 seconds (process running for 0.625)
2025-06-19T10:14:38.129-07:00 INFO 65736 --- [ main] o.s.s.ResourcePrinter : classpath:/native-resource.txt content:
Testing native resources on MacOS.
2025-06-19T10:14:38.130-07:00 INFO 65736 --- [ main] o.s.s.ResourcePrinter : classpath:/custom-resource.txt content:
Testing custom resources.
BUILD SUCCESSFUL in 9s
Log4J 2.25.0 https://github.com/sdkotlin/sd-kotlin-spring-talks/tree/b15de4858a0c10ab9c267489b1b5a98cf1a9e10d
> Task :subprojects:app:run
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| | ) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v3.5.1)
You've been scanned.
BUILD SUCCESSFUL in 1s
That one output "You've been scanned" line is a plain old println(): https://github.com/sdkotlin/sd-kotlin-spring-talks/blob/b15de4858a0c10ab9c267489b1b5a98cf1a9e10d/subprojects/app/src/main/kotlin/org/sdkotlin/springdemo/SpringBootApp.kt#L45.
Comment From: wilkinsona
Thanks for the report. Given that the only change you've made is to the Log4j2 version, it would suggest that the cause lies in that project. As such, I'm curious why you've opened an issue here rather than there. If you've done some analysis that points to a problem caused by Spring Boot, please share it with us
Comment From: wilkinsona
https://github.com/apache/logging-log4j2/commit/b23e9a56a9cc9eed8c48241555256db8647e917a is a breaking change from Spring Boot's perspective. We call LoggerContext.start(Configuration) on a LoggerContext in STARTED state. This used to result in setConfiguration(Configuration) being called. Since these changes in Log4j2, that no longer happens so Boot's configuration isn't applied. Perhaps we can do something differently that will work with both 2.25.0 and earlier versions but I think this should be investigated by the Log4j2 team in the first instance. I'll close this one for now, we can re-open it if that investigation identifies a change that could be made in Boot to tolerate the change in Log4j2's behavior.