Pentaho reporting flow engine is a free java report library.

it has the following features:
* full on-screen print preview;
* data obtained via swing's tablemodel interface
(making it easy to print data directly from your application);
* xml-based report definitions;
* output to the screen, printer or various export formats
(pdf, html, csv, excel, plain text);
* support for servlets (uses the jfreereport extensions)
* extensive documentation in acrobat pdf format, plus full javadocs;