he purpose of the Jakarta POI open source project is to provide Java with the ability to manipulate file formats based on Microsoft's OLE 2 Compound Document Format. Currently, the most widely accepted part of the project is the Horrible Spread Sheet Format (HSSF) (click the link to discover a bit of the history behind that name.

HSSF provides:

• An environmental API for read-only access to Excel (97-2000) format.
• A full user model API for creating, reading and modifying the Excel files.

The HSSF framework is divided into the following packages (see Table 1).

Table 1: Packages in the HSSF framework. The table lists the packages in the HSSF framework and the purpose of each.

Package	Purpose
org.apache.poi.hssf.eventmodel	Handles different events generated in the process of reading and writing Excel documents.
org.apache.poi.hssf.eventusermodel	Provides classes to read Excel documents.
org.apache.poi.hssf.record.formula	Contains classes to handle FORMULA used in Excel document.
org.apache.poi.hssf.usermodel	Contains classes to generate Excel documents.
org.apache.poi.hssf.util	Contains utility classes to handle different attributes of the Excel document.

Using these packages you can interact with existing Excel documents and create new ones. Before starting to develop the example, here's a brief explanation of how the POI models an Excel document.