java-config --classpath on slotted library

Hi,

how do I get java-config to give me the classpath of a slotted
library? On my system I have dev-java/bsf:2.3 installed, and running

$ java-config --classpath=bsf
!!! ERROR: Package bsf was not found!

gives me an error. For dev-java/fontbox:0 it works on the other hand:

$ java-config --classpath=fontbox
/usr/share/fontbox/lib/fontbox.jar

but fails once I install dev-java/fontbox:1.7. Am I missing some
command line argument?

Thanks,

nick