user reported:
I tried to use jpackage file-associations option to associate a given
extension. This works fine. The program gets launched with the given
argument (e.g., double clicking file on Windows).

I have noticed though that the argument may be split due to possible
whitespaces in the filename.

e.g., clicking on file C:\foo.xyz works fine but C:\part1 part2.xyz gets
broken up into 2 arguments.
It looks the argument needs to be wrapped in quotes so that a Java program
gets the right argument:

["C:\part1 part2.xyz"]
instead of
["C:\part1", "part2.xyz"]
as currently reported.