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I have a problem with conflicting dependencies in my project. Particularly, there are two implementations of slf4j logging: slf4j-simple and logback-classic, and I'm getting

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/apykhtin/.m2/repository/org/slf4j/slf4j-simple/1.7.19/slf4j-simple-1.7.19.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/apykhtin/.m2/repository/ch/qos/logback/logback-classic/1.1.3/logback-classic-1.1.3.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 [org.slf4j.impl.SimpleLoggerFactory]
Exception in thread "main" java.lang.IllegalStateException: Unable to acquire the logger context
        at io.dropwizard.logging.LoggingUtil.getLoggerContext(LoggingUtil.java:46)

at runtime.

logback-classic is a must-have dependency for me (because of dropwizard), but slf4j-simple is not really, and I'd like to drop it from my uber project. Only it's not that easy.

My "uber jar" has a dependency on "small jar", which, in turn, has a dependency on "slf4j-simple". Putting an exclusion in uber jar's pom is not helping:

<dependency>
    <groupId>com.my.unique.group</groupId>
    <artifactId>small-jar</artifactId>
    <version>0.1.2-SNAPSHOT</version>
    <exclusions>
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
        </exclusion>
    </exclusions>
</dependency>

I think because small-jar is "shaded". My "uber-jar" is using maven-shade-plugin, while "small-jar" is not. I also tried to exclude slf4j-simple from shading:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>1.6</version>
    <configuration>
    <artifactSet>
        <excludes>
            <exclude>org.slf4j:slf4j-simple:jar</exclude>
        </excludes>
    </artifactSet>
    ...
</plugin>

but also without success. slf4j-simple still gets included in my uber-jar. So far my development was all related to "uber-jar". It is possible for me to make changes to "small-jar" code, but I'd like to avoid that.

What am I doing wrong?

Alexander
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  • Update: maven-shade-plugin is not the culprit here. I turned this plugin completely off, and still getting exactly the same error. – Alexander May 04 '16 at 18:50
  • Update 2: Apparently my problems were caused by project misconfiguration. After clearing everything (including maven repository), checking out fresh sources and creating project in Eclipse from scratch, everything is working as expected. Thank you everybody. – Alexander May 05 '16 at 00:07

2 Answers2

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im not sure what you mean with "uber-jar". parent project?!

any way use mvn dependency:tree -Dincludes=:slf4j* to see where it comes from, then define the dependency in the lower project and exclude the transitive as you have done above

hope this helps

Hisham Khalil
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  • Thanks, Hisham. By "uber-jar" I mean my master, top-level project. Curiousli, slf4j-simple is not in maven dependency tree, but somehow it gets into the master jar anyways. – Alexander May 04 '16 at 16:30
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Why is small-jar being shaded? It seems like you could just let maven handle the transitive dependency of slf4j when compiling small-jar as a non-shaded artifact, and then when you depend on small-jar in your "uber-jar", exclude the necessary transitive dependencies (which would be slf4j). Once its shaded, maven isn't going to be able to exclude the dependencies since for all it knows, everything in small-jar is a single dependency.

I see you want to avoid making changes to small-jar, but this is one of the inherent problems with shading in general. I would recommend either not shading small-jar at all, or at least exclude slf4j from the small-jar shading and let maven handle it as a normal transitive dependency that can be excluded in your uber-jar's dependency configuration.

alexanderific
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  • So far (according to maven's build messages) I was able to exclude small-jar from shading. However, this did not stop uber-jar from pulling in slf4j-simple, even though it is explicitly listed as a dependency exclusion. – Alexander May 04 '16 at 18:42
  • Is small-jar the only dependency uber jar has? It's possible another dependency is bringing it in and you will need to globally exclude it. – alexanderific May 05 '16 at 02:57
  • Worthy of checking, but no, other projects did not bring slf4j-simple. – Alexander Apr 06 '18 at 17:37