如何在SpringBoot中同时使用log4j和logBack？

Question

Our software uses an api (filenet p8) that requires log4j to be configured. We use logBack and Spring Boot. I notice that to use log4j in Spring Boot we have to exclude logBack. This is not possible. Is there a way to run log4j and logBack in parallel in Spring Boot? Thanks

Answer 1

The spring-boot-starter-logging artifact enables the automatic configuration and redirection of many logging frameworks to Logback.

However since Spring Boot 2.x the redirections from Log4j 1.2 and JCL to SLF4J are not installed by default. You need to install:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>log4j-over-slf4j</artifactId>
</dependency>

which is a drop-in replacement of Log4j 1.2 that redirects everything to SLF4J (no <version> attribute needed, since Spring Boot manages it).

You must also remove the log4j and slf4j-log4j12 artifacts, if they are present: the first one would cause random class loading ( log4j-over-slf4j has the same classes), the second one will cause an infinite loop between Log4j and SLF4J (cf. this question ).