Scott Klement wrote some articles for iSeries Network that explain 
how to use Java POI/HSSF classes to read and write directly to 
Excel spreadsheets:


How to Excel with RPG and Java
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=19277

How to Excel with RPG and Java, Part 2
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=19336

How to Excel with RPG and Java, Part 3
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=19591

HSSF Fills and Colors
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=19606

How to Update an HSSF Spreadsheet
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=19585

HSSF Word Wrapping
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowIssueArticles&webID=1001&newsID=5012&issueID=5186

Parsing an Excel Spreadsheet with RPG and Java
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=17839

Parsing an Excel Spreadsheet, Part 2
http://www.iseriesnetwork.com/resources/clubtech/index.cfm?fuseaction=ShowNewsletterIssue&ID=18396