i don't know excel-to-pdf, but looking at this as a java-to-pdf issue, here are some potentials...
iText is a java pdf library:
http://www.lowagie.com/iText/ also, if you want to get into the xml world, you can go excel-to-xml-to-pdf. the xml-to-pdf part would be handled using xslt and xsl-fo (see
http://xml.apache.org/fop/ for an example).
lastly, jfreereport does pdf generation:
http://www.object-refinery.com/jfreereport/