Weijie Sun created TINKERPOP-3014:
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Summary: Dependencny jcl-over-slf4j in gremlin-core is declared
but unused due to dependency conflict.
Key: TINKERPOP-3014
URL: https://issues.apache.org/jira/browse/TINKERPOP-3014
Project: TinkerPop
Issue Type: Bug
Reporter: Weijie Sun
h2. Problem Description
"gremlin-core" declares "jcl-over-slf4j" as its dependency. However, it seems
that the dependency is actually unused due to a dependency conflict.
There is another dependency "commons-logging:commons-logging" in the dependency
tree as listed below:
{code:java}
org.apache.tinkerpop:gremlin-core:jar:3.7.0-SNAPSHOT
\- org.apache.commons:commons-configuration2:jar:2.9.0:compile
\- commons-logging:commons-logging:jar:1.2:compile
\- org.slf4j:jcl-over-slf4j:jar:1.7.33:compile{code}
The classes in "jcl-over-slf4j" are also in "commons-logging" as listed below:
{code:java}
[INFO] org.apache.commons.logging.impl.NoOpLog
[INFO] org.apache.commons.logging.impl.SimpleLog$1
[INFO] org.apache.commons.logging.impl.SimpleLog
[INFO] org.apache.commons.logging.impl.SLF4JLocationAwareLog
[INFO] org.apache.commons.logging.impl.SLF4JLog
[INFO] org.apache.commons.logging.impl.SLF4JLogFactory
[INFO] org.apache.commons.logging.Log
[INFO] org.apache.commons.logging.LogConfigurationException
[INFO] org.apache.commons.logging.LogFactory{code}
The problem is that "commons-logging" is ahead of "jcl-over-slf4j" in the
dependency tree, thus ahead of "jcl-over-slf4j" in the classpath. When multiple
JAR files contain the same class, the class loader will load the first
occurrence it finds based on the classpath order. This means the classloader
will select classes in "commons-logging" instead of "jcl-over-slf4j".
So despite "jcl-over-slf4j" being declared directly, it's actually unused.
"commons-logging" is the actual used dependency, causing confusion.
h2. Possible Solution
Change the order of "jcl-over-slf4j" and "commons-logging" so that
"jcl-over-slf4j" appears ahead of "commons-logging" in the classpath. In this
way, "jcl-over-slf4j" is used as intended.
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