Setting up log4j functionality for a custom plugin isn't trivial. If you meet:

log4j:ERROR A "org.apache.log4j...." object is not assignable to a "org.apache.log4j...." variable.
log4j:ERROR The class "org.apache.log4j...." was loaded by
log4j:ERROR [WebappClassLoader]

like errors, in our case, the solution was to add the parameter


to JAVA_OPTS in joget-start.bat.

It's just a workaround, though. Somehow, the proper way would be to use log4j as an osgi service.