HSSF is the POI Project's pure Java implementation of the Excel '97(-2002) file format.

HSSF provides a way to read spreadsheets create, modify, read and write XLS spreadsheets It provides:

• low level structures for those with special needs
• an eventmodel api for efficient read-only access
• a full usermodel api for creating, reading and modifying XLS files

An alternate way of generating a spreadsheet is via the Cocoon serializer (yet you'll still be using HSSF indirectly). With Cocoon you can serialize any XML datasource (which might be a ESQL page outputting in SQL for instance) by simply applying the stylesheet and designating the serializer.

If you're merely reading spreadsheet data, then use the eventmodel api in the org.apache.poi.hssf.eventusermodel package.

If you're modifying spreadsheet data then use the usermodel api. You can also generate spreadsheets this way.