one other sort of bridge is the keystroke bridge where the Java
program types and the keystrokes are fed via JNI into Excel or some
other windows program. It is typing blind.

There of course there are CSV files which have just data but no
formulae. These are easy to create and read in java. See
http://mindprod.com/jgloss/csv.html

I worked on a Java spreadsheet engine that could import and export
Excel files.  Unfortunately the company went belly up.
I did the JavaDoc for it.  We must have got the Excel format docs
somewhere to write it.

I guess it depends what is going wrong with the POI approach - is it
something like bad formatting? It might help to move as much processing
as possible into an Excel VBA macro, and use POI or Bridge2Java to
drive the macros. Horrible bodge, I know, but it might work.

Paul