[FIXED] SLF4J Logback LoggerContext Conflicts

Issue

I am working on deploying a spring boot executable jar for my application. Im using SLF4J logging, and when I build and run inside of IntelliJ I have no issues.

However, when I try to run the .jar, from the command line I get a LoggerFactory is not a Logback LoggerContext but Logback is on the classpath exception.

It complains about the slf4j-log4j12-1.7.12.jar in two places /opt/mapr/lib/ and /opt/mapr/hadoop/hadoop-2.7.0/share/hadoop/common/lib/.

If i remove the jar from both places and run my app:

java -cp $(mapr classpath):MapRProducerApp-0.0.1-SNAPSHOT.jar org.springframework.boot.loader.PropertiesLauncher

it will then fail startup due to SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".

I dont understand why it would fail saying faild to load the slf4j class when my apps .jar is built with that dependency through

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>

In IntelliJ, I am bringing in all external dependencies that exist inside the /opt/mapr/lib folder, which includes the slf4j-log4j12-1.7.10.jar, but IntelliJ does not give the Logback LoggerContext error.

To recap here:

• Building and running the jar on its own works, but will fail because it needs dependencies that exist inside the mapr classpath.
• Running the jar with the mapr classpath fails because of the slf4j jar inside /opt/mapr/lib.
• Removing that jar leads to another failure about a slf4j jar in /opt/mapr/hadoop/hadoop-2.7.0/share/hadoop/common/lib/.
• Removing that jar then fails the app because it now cannot find any slf4j binding.

Is there something im missing? Do I need to package my app a certain way so it does not include the SLF4J dependency?

Solution

I'm not clear about your <dependencies> hierarchy, but by adding <exclusion> you can simply resolve the conflict.

<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>

Answered By - Denuwan.hh