Last week, I wrote a post that described how to hack the Maven dependency resolution system. I admit it was a dirty hack, it’s even in the post name.
But I got it wrong. Thanks Stéphane Nicoll for pointing it out:
"It boils down to excluding the spring-boot-starter-logging in every Spring Boot starter"
— Stéphane Nicoll (@snicoll) December 14, 2020
Since you've put every in bold, I assume you meant it. That's actually wrong and not what the documentation states.
Here is an example: https://t.co/JKgPXCh0Nb
Even though I linked the documentation, I misread it. Here’s my mea culpa.
As Stéphane states, you can exclude the default dependency from the parent spring-boot-starter starter:
pom.xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>Let’s check the mvn dependency:tree output:
[INFO] com.example:demo:jar:0.0.1-SNAPSHOT
[INFO] +- org.springframework.boot:spring-boot-starter:jar:2.4.1:compile (2)
[INFO] | +- org.springframework.boot:spring-boot:jar:2.4.1:compile
[INFO] | | \- org.springframework:spring-context:jar:5.3.2:compile
[INFO] | +- org.springframework.boot:spring-boot-autoconfigure:jar:2.4.1:compile
[INFO] | +- jakarta.annotation:jakarta.annotation-api:jar:1.3.5:compile
[INFO] | +- org.springframework:spring-core:jar:5.3.2:compile
[INFO] | | \- org.springframework:spring-jcl:jar:5.3.2:compile
[INFO] | \- org.yaml:snakeyaml:jar:1.27:compile
[INFO] +- org.springframework.boot:spring-boot-starter-log4j2:jar:2.4.1:compile (1)
[INFO] | +- org.apache.logging.log4j:log4j-slf4j-impl:jar:2.13.3:compile
[INFO] | | +- org.slf4j:slf4j-api:jar:1.7.30:compile
[INFO] | | \- org.apache.logging.log4j:log4j-api:jar:2.13.3:compile
[INFO] | +- org.apache.logging.log4j:log4j-core:jar:2.13.3:compile
[INFO] | +- org.apache.logging.log4j:log4j-jul:jar:2.13.3:compile
[INFO] | \- org.slf4j:jul-to-slf4j:jar:1.7.30:compile
[INFO] +- org.springframework.boot:spring-boot-starter-actuator:jar:2.4.1:compile (2)
[INFO] | +- org.springframework.boot:spring-boot-actuator-autoconfigure:jar:2.4.1:compile
[INFO] | | +- org.springframework.boot:spring-boot-actuator:jar:2.4.1:compile
[INFO] | | +- com.fasterxml.jackson.core:jackson-databind:jar:2.11.3:compile
[INFO] | | | +- com.fasterxml.jackson.core:jackson-annotations:jar:2.11.3:compile
[INFO] | | | \- com.fasterxml.jackson.core:jackson-core:jar:2.11.3:compile
[INFO] | | \- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.11.3:compile
[INFO] | \- io.micrometer:micrometer-core:jar:1.6.2:compile
[INFO] | +- org.hdrhistogram:HdrHistogram:jar:2.1.12:compile
[INFO] | \- org.latencyutils:LatencyUtils:jar:2.0.3:runtime| 1 | The Log4J2 starter is present as expected |
| 2 | None of the starters brings in the SLF4J dependency |
Besides that specific point, there are a couple of unrelated lessons:
- Remember to check the documentation
- Remember to check the documentation once more
- Be surrounded by people who are willing to help correct you
- Admit when you’re wrong
- Most importantly, it’s less damaging to your pride to ask for feedback before posting than to publish such a fixing post after