What is "apache-poi"

The project Apache POI has the mission to create and maintain Java Apis to handle various standards-based file formats Open Office XML (OOXML) and format of composite documents OLE2 from Microsoft. With it, it is possible to read and write data in Word files, excel, Powerpoint and Outlook.

Some frameworks known as the primefaces and the Richfaces use it to export data from a DataTable directly to an Excel file.