ERROR SLF4J: Class path contains multiple SLF4J bindings jenkins cobertura maven - maven

Question

I'm with this error on third day already and I can't resolved. There is something that I can't grasp on and no matter what I do the error still persists.
I'm reading a book called "Jenkins a definitive guide" (http://www.wakaleo.com/books/jenkins-the-definitive-guide) and I'm stuck on chapter two. Basically is a example of how to use Jenkins with Javadoc, JUnit and Cobertura plugin for Jenkins. Everything works until I get to Cobertura plugin part, where I get next error:
[ERROR] SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/C:/Windows/System32/config/systemprofile/.m2/repository/ch/qos/logback/logback-classic/1.0.13/logback-classic-1.0.13.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/C:/Windows/System32/config/systemprofile/.m2/repository/org/slf4j/slf4j-simple/1.6.1/slf4j-simple-1.6.1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]
I have seen other problems like mine and the conclusion I got is that I have either to include o exclude a dependency in my pom.xml file/s (this examples only uses pom files at this stage). My pom.xml file that has slf4j-simple looks like this:
<project>
......
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.6.1</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.6.1</version>
</dependency>
</dependencies>
</project>
and there is no explicit dependency to logback-classic hence I don't know in what dependency is being used. I tried to use dependency plugin for jenkins and I got this result:
[INFO] --- maven-dependency-plugin:2.8:tree (default-cli) # gameoflife-web ---
[INFO] com.wakaleo.gameoflife:gameoflife-web:war:1.0-SNAPSHOT
[INFO] +- com.wakaleo.gameoflife:gameoflife-core:jar:1.0-SNAPSHOT:compile
[INFO] +- org.springframework:spring-webmvc:jar:3.0.2.RELEASE:compile
[INFO] | +- org.springframework:spring-asm:jar:3.0.2.RELEASE:compile
[INFO] | +- org.springframework:spring-beans:jar:3.0.2.RELEASE:compile
[INFO] | +- org.springframework:spring-context:jar:3.0.2.RELEASE:compile
[INFO] | | \- org.springframework:spring-aop:jar:3.0.2.RELEASE:compile
[INFO] | +- org.springframework:spring-context-support:jar:3.0.2.RELEASE:compile
[INFO] | \- org.springframework:spring-expression:jar:3.0.2.RELEASE:compile
[INFO] +- org.springframework:spring-core:jar:3.0.2.RELEASE:compile
[INFO] | \- commons-logging:commons-logging:jar:1.1.1:compile
[INFO] +- org.springframework:spring-web:jar:3.0.2.RELEASE:compile
[INFO] | \- aopalliance:aopalliance:jar:1.0:compile
[INFO] +- javax.servlet:jstl:jar:1.2:compile
[INFO] +- javax.servlet:servlet-api:jar:2.5:provided
[INFO] +- org.mockito:mockito-all:jar:1.8.5:test
[INFO] +- org.easytesting:fest-assert:jar:1.4:compile
[INFO] | \- org.easytesting:fest-util:jar:1.1.6:compile
[INFO] +- org.slf4j:slf4j-simple:jar:1.6.1:compile
[INFO] +- org.slf4j:slf4j-api:jar:1.6.1:compile
[INFO] +- junit:junit:jar:4.11:test
[INFO] | \- org.hamcrest:hamcrest-core:jar:1.3:test
[INFO] \- org.hamcrest:hamcrest-all:jar:1.1:test
Maybe I'm blind, but I still can't see who uses logback-classic (by the way I'm not sure what values are correct for and for logback-classic).
I tried to remove the slf4j dependency's and I error is gone, but I don't get any cobertura reports. I tried to exclude logback-classic with
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.6.1</version>
<exclusions>
<exclusion>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.6.1</version>
<exclusions>
<exclusion>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
</exclusion>
</exclusions>
</dependency>
and the error persists.
I don't know what to do anymore, please help!

Answer 1

The good news is that even if SLF4J is reporting an error, it's actually warning you that SLF4J will be bound to ch.qos.logback.classic.util.ContextSelectorStaticBinder since there are two bindings available on the class path. SLF4J will pick the first one available on the class path. Your application should continue to work just fine albeit logging with logback.
I can't tell you why logback-classic.jar is on the class path but I suggest you investigate the "System profile" mentioned in the class path.

Answer 2

You are trying to exclude the logback-classic from the slf dependency itself. The issue is that as mentioned here, you were using more than one binding in your class path. Actual way is to keep exclusion for logback-classic, in the dependency which uses it and not in your slf4j dependency. Unfortunately, I am not sure which of your jars, are having a reference to slf4j which is causing the issue. One workaround is, use Ctrl+Sft+T to see the existence of the StaticLoggerBinder class, in different jars, and place the logback-classic exclusion in that. Other work around is, you can try keeping exclusion, as trial and error. These are just work arounds, but the concept is same. We need to find other dependency which has reference to logback-classic in your classpath

Answer 3

Please follow the below
Steps
Step1: Identify the classic logback using the mvn dependency:tree
Step2: Add the below exclusion in pom.xml
<exclusions>
<exclusion>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
</exclusion>
<exclusion>
<groupId>org.apache.logging.log4j</groupId>
<artifactId>log4j-to-slf4j</artifactId>
</exclusion>
</exclusions>
Step3: Test the application
Credits go to the https://java2blog.com/fixed-slf4j-warning-class-path-contains-multiple-slf4j-bindings/