METRON-2314 HDFSIndexingIntegrationTests Fails with SLF4J/Log4j Delegation Loop

[nickwallen]

After merging #1557 from master into the feature/METRON-2088-support-hdp-3.1 feature branch, the HDFSIndexingIntegrationTest fails.

Tests run: 1, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 0.185 sec <<< FAILURE! - in org.apache.metron.indexing.integration.HDFSIndexingIntegrationTest
test(org.apache.metron.indexing.integration.HDFSIndexingIntegrationTest)  Time elapsed: 0.177 sec  <<< ERROR!
java.lang.ExceptionInInitializerError
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:264)
	at org.slf4j.impl.Log4jLoggerFactory.<clinit>(Log4jLoggerFactory.java:48)
	...
Caused by: java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar AND slf4j-log4j12.jar on the class path, preempting StackOverflowError. See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more details.
	at org.apache.log4j.Log4jLoggerFactory.<clinit>(Log4jLoggerFactory.java:49)
	... 37 more

Results :

Tests in error:
  HDFSIndexingIntegrationTest>IndexingIntegrationTest.test:72->BaseIntegrationTest.getKafkaComponent:29 » ExceptionInInitializer

Root Cause

It doesn't make sense for a project to pull-in both slf4j-log4j12 and log4j-over-slf4j. The purpose of slf4j-log4j12 is intended to redirect calls made to an SLF4J logger to Log4j. The purpose of log4j-over-slf4j is to redirect calls made to a Log4j logger to SLF4J. Pulling in both would cause endless indirection except for the specific check for this error performed by SLF4j. See the SLF4j documentation here for more information.

The metron-indexing-storm project was pulling in log4j-over-slf4j incorrectly as a transitive. This needs to be explicitly excluded.

Acceptance Testing

The integration tests should pass.

Pull Request Checklist

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[mmiklavc]

What are we actually doing with log4j-over-slf4j at all? On the surface it seems like we should standardize on slf4j-log4j12 so that we depend exclusively on the slf4j api and route to log4j for the backend logging impl.

[nickwallen]

We don't do anything with log4j-over-slf4j. Its a storm-core dependency.

[nickwallen]

This just restores one of the exclusions that existed prior to #1557.

[mmiklavc]

+1, thanks @nickwallen

[nickwallen]

Thanks for the review. This has been merged into the feature branch.