slf4j version conflict while building with Maven

Question

I realised that one of my projects uses slf4j 1.5.8 and Hibernate uses slf4j 1.6. While building with Maven it downloads both jars but I guess the class files of 1.5.8 are used. So, when I run the program i get following error:

SLF4J: The requested version 1.5.8 by your slf4j binding is not compatible with [1.6] 

In pom.xml I have put

<dependencyManagement>         <dependency>         <groupId>org.slf4j</groupId>         <artifactId>slf4j-api</artifactId>         <version>1.6.1</version>     </dependency> </dependencyManagement> 

The 1.5.8 is part of dependency so it's downloaded on its own.

Answer 1

As you discovered yourself, there are two libraries (Hibernate and some other) transitively importing SLF4J in two different versions. Unfortunately the older version is being picked up by maven (there are some rules which dependency should be chosen by maven in this situation). The solution is to add the exclusion in the dependency that imports older version of SLF4J (com.example:foo-bar is example here):

<dependency>   <groupId>com.example</groupId>   <artifactId>foo-bar</artifactId>   <version>1.2.3</version>    <exclusions>      <exclusion>         <groupId>org.slf4j</groupId>         <artifactId>slf4j-api</artifactId>      </exclusion>    </exclusions> </dependency> 

If you still experience this problem, issue:

$ mvn dependency:tree 

Look for 1.5.8 version and exclude it from all libraries importing it.

Answer 2

Excluding is quite unnecessary and maybe quite misleading. Instead, explicitly include the slf4j-api with the desired version in your projects pom file. That's it!

This approach takes advantage of Maven's transitivity rules: the nearest dependency declaration wins.