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
Web-based data-entry and consolidation of
Excel data with multi-user capability
Transformation of local Excel solutions in
corporate-wide web applications
Ad-Hoc delivery of IT solutions in the inter-
company und intra-company sphere
Excel as Rapid-Development Tool for web applications in Finance, Sales and Controlling
Read Tony Sintes's entire Java/Microsoft Excel series (JavaWorld):
"The Java-Excel Solution Revisited"
It's a great frontend to edit data that you want to display on a web page. For structured output of data in CVS format see the HTML table classes.