Maven Class path error multiple SLF4J bindings

I have been getting this error while trying to do a MAVEN INSTALL. I tried exclusions, but not sure the where to include in pom file. Let me how and what exclusion tags should i include in my pom file. I am also attaching my pom file snippet where to include the exclusions`SLF4J: Class path contains multiple SLF4J bindings.

SLF4J: Found binding in
[jar:file:/C:/Users/147188/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]

SLF4J: Found binding in
[jar:file:/C:/Users/147188/.m2/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.10.0/log4j-slf4j-impl-2.10.0.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]

POM file:

<!-- Start of required part to make log4j work -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>

<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
<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>
<exclusions>
<exclusion>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</exclusion>
</exclusions>
</dependency>
<!-- End of required part to make log4j work -->


1 Answer
1

That message indicates that you are bringing in both logback-classic and log4j-slf4j-impl, which both want to be the logging framework for SLF4J to bind to. If you're not sure which dependency is bringing in which other dependencies, I find it very useful to run "mvn dependency:tree" to see the tree of dependencies being used. That should give you enough information to figure out which logging framework binding you need to exclude.

As the documentation that the warning points to you says,

Embedded components such as libraries or frameworks should not declare a dependency on any SLF4J binding but only depend on slf4j-api. When a library declares a compile-time dependency on a SLF4J binding, it imposes that binding on the end-user, thus negating SLF4J's purpose. When you come across an embedded component declaring a compile-time dependency on any SLF4J binding, please take the time to contact the authors of said component/library and kindly ask them to mend their ways.

You pretty much want to exclude all actual logging frameworks from all dependencies, so that the only logging framework being used is the one you've explicitly added. I even often find it useful to set up some maven-enforcer-plugin bannedDependencies rules to ensure that I don't accidentally bring in another logging framework when updating my dependencies. It can also be helpful to use dependencyManagement sections in your POM to ensure that all your dependencies use the same version of slf4j-api.

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