Hey, POI is pretty good, but I think if you want a really good Java Excel tool with commercial support that you should check out ExtenXLS.

We use and recommend the Java Excel API ExtenXLS, which you can download here from Extentech's web site at:
DOWNLOAD NOW!

This tool is so slick and works so well, we've never even needed support!

Used by JPMorgan/Chase, HP, Ford, and more, so you know it's solid...