From the Developer Library website:
To initialize the export control
- To set the report source of the control, call its setReportSource method.
For information about how to get a report source, see How to get a report source from the Java Reporting Component.
exportControl.setReportSource(reportSource);
- To call the setExportOptions method of the control, pass it an ExportOptions object.
exportControl.setExportOptions(exportOptions);
- Set the ExportAsAttachment property to true, if you want give users the option to open the exported file or save the file to disk.
When ExportAsAttachment is False, the file is automatically displayed in the application that is associated with the type of the exported file. Users then need to save the file from inside the application.
exportControl.setExportAsAttachment(true);
Note: If setExportAsAttachment is set to false, the report is opened in the user's browser window, if the browser supports that type of file.
If you look at item 3, you'll see that setting the setExportAsAttachment flag will allow the user to either open or save the attachment to a file. This is probably not exactly what you're looking for, but it may be a step in the right direction.
There is sample code for saving an exported CSV file that you might be able to adapt for your purposes.
-Dell