Maven SL4J multiple bindings, previous solutions fail

Question

I have a project that has multiple SLF4J bindings. I have read and tried the solutions in this SO post, this other SO post and the slf4j website.

What I see if this when I run the code is

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/Mike/.m2/repository/org/jlab/coat/coat-libs/5.1-SNAPSHOT/coat-libs-5.1-SNAPSHOT.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/Mike/.m2/repository/org/slf4j/slf4j-log4j12/1.7.16/slf4j-log4j12-1.7.16.jar!/org/slf4j/impl/StaticLoggerBinder.class]

However in my pom.xml file, I already have

    <dependency>
        <groupId>org.jlab.coat</groupId>
        <artifactId>coat-libs</artifactId>
        <version>5.1-SNAPSHOT</version>
        <exclusions>
            <exclusion>
                <groupId>org.slf4j</groupId>
                <artifactId>slf4j-log4j12</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

and in the mvn dependency:tree I do not see this dependency for the exclusion jar, only for the Spark jar, i.e.

[INFO] com.IKP:DCdatabase:jar:0.0.1-SNAPSHOT
[INFO] +- org.jlab.coat:coat-libs:jar:5.1-SNAPSHOT:compile
[INFO] +- org.apache.spark:spark-core_2.11:jar:2.2.1:compile
...
...
...
[INFO] |  +- org.slf4j:slf4j-api:jar:1.7.16:compile
[INFO] |  +- org.slf4j:jul-to-slf4j:jar:1.7.16:compile
[INFO] |  +- org.slf4j:jcl-over-slf4j:jar:1.7.16:compile
[INFO] |  +- log4j:log4j:jar:1.2.17:compile
[INFO] |  +- org.slf4j:slf4j-log4j12:jar:1.7.16:compile

I have also tried a few more steps, such as clean out my .m2 directory, and build all sources from scratch, but I still see this double binding.

The nuance that occurs is that the log suppression for Spark does occur, i.e.

    Logger.getLogger("org.apache.spark.SparkContext").setLevel(Level.WARN);
    Logger.getLogger("org").setLevel(Level.OFF);
    Logger.getLogger("akka").setLevel(Level.OFF);

No longer set the levels to off and I see all the levels.

Is there another way to remove this multiple binding for SLF4J?

Kit Menke · Accepted Answer · 2018-05-25T14:22:04.867

It looks to me like coat-libs has been packaged as an uber jar which is why slf4j doesn't show up as a dependency when you do mvn dependency:tree. This explains why your exclusion isn't working.

I would recommend taking a look at the maven shade plugin for packaging your jar. Then, you can use a filter to exclude the slf4j dependencies from coat-libs using a filter.

For example, maybe something like:

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-shade-plugin</artifactId>
        <version>3.1.1</version>
        <executions>
          <execution>
            <phase>package</phase>
            <goals>
              <goal>shade</goal>
            </goals>
            <configuration>
              <filters>
                <filter>
                  <artifact>org.jlab.coat:coat-libs</artifact>
                  <excludes>
                    <exclude>org/slf4j/**</exclude>
                  </excludes>
                </filter>
                <filter>
                  <artifact>*:*</artifact>
                  <excludes>
                    <exclude>META-INF/*.SF</exclude>
                    <exclude>META-INF/*.DSA</exclude>
                    <exclude>META-INF/*.RSA</exclude>
                  </excludes>
                </filter>
              </filters>
            </configuration>
          </execution>
        </executions>
      </plugin>
    </plugins>
  </build>

I am accepting this answer because the multiple bindings statement no longer appears. But for some reason this still did not fix the logger from funneling everything but "Warn" — mkunkel, May 25 '18 at 17:44

score 0 · Answer 2 · answered May 25 '18 at 12:57

Just like the message says, you're getting one binding from coat-libs-5.1-SNAPSHOT.jar, and another binding in slf4j-log4j12-1.7.16.jar. It's not that "coat-libs" is trying to bring in a dependency that has a binding, it is a logging binding that's trying to handle SLF4J logging. You can only use one logging binding, so you either need to remove the usage of coat-libs, or you need to exclude slf4j-log4j12 from the dependencies for spark-core, depending on which logging framework you're actually trying to use.

Thanks for the answer, but as my title says, your approach of excluding one binding does not work. For instance, if I exclude the binding from spark-core, then spark does not understand where to get the binding from. If I try to exclude from the uber jar of clas, nothing gets excluded. — mkunkel, Jun 07 '18 at 14:21

Maven SL4J multiple bindings, previous solutions fail

2 Answers2