In Java Web Start 1.5 or 1.4 or even earlier it is possible to inspect
Java Web Start Cache directly and find out what modules are there on a
file system level.

This is no longer possible beginning with Java Web Start 6, due to a new
cache format.

It is possible however to view a list of "Applications" or "Resources"
loaded into the Java Web Start cache.
Unfortunately, it is not possible to get any of this lists printed to file.

This RFE suggests to be able to print the lists of the Java Web Start 6
Cache Viewer to file.