LensKit and Grapht use SLF4J throughout for their logging, and can log rather verbosely. LensKit's binary packages and command-line scripts use Logback as underlying logging service, while the Maven plugin installs a shim that implements the SLF4J APIs in terms of the Maven logger.

Some Guava code logs errors to the logging facilities in java.util.logging. Therefore, if you are building an application with LensKit and using a SLF4J other than slf4j-jdk14 (and we really don't recommend using the JDK14 implementation), you probably want to configure jul-to-slf4j, as documented here.