$ mvn dependency:analyse12 February 2020
Note on usage of Maven's dependency plugin for analyzing project dependencies.
When implementing an application I usually use the logging facade slf4j. When
double-checking the dependencies of such a project with
$ mvn dependency:analysethe plugin often reports
[WARNING] Unused declared dependencies found:
[WARNING] org.slf4j:slf4j-log4j12:jar:1.7.26:testBut without declaring the reported slf4j-log4j as dependency, the tests
suppress the log output entirely. The reason for this is that slf4j logging
facade looks up available implementations of the facade interface by reflection.
If no implementation like the slf4j-log4j is found, the no-op logger is
installed and no logging output is generated.
But we cannot blame the Maven dependency plugin, because it can only consider dependencies explicitly defined in the POM, and not libraries resolved by reflection.
The scope of the slf4j-log4j artifact is just test, because at runtime the
application server provides an appropriate implementation of the logging facade
interface.
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