Apache POI, a project run by the Apache Software Foundation, and previously a sub-project of the Jakarta Project, provides pure Java libraries for reading and writing files in Microsoft Office formats, such as Word, PowerPoint and Excel.
The name was originally an acronym for "Poor Obfuscation Implementation", referring humorously to the fact that the file formats seemed to be deliberately obfuscated, but poorly, since they were successfully reverse-engineered. This explanation – and those of the similar names for the various sub-projects – were removed from the official web pages in order to better market the tools to businesses who would not consider such humor appropriate. The original authors Andrew C. Oliver and Marc Johnson also noted the existence of the Hawaiian poi dish, made of mashed taro root, which had similarly derogatory connotations.
POI supports the ISO/IEC 29500:2008 Office Open XML file formats since version 3.5. A significant contribution for OOXML support came from Sourcesense, an open source company which was commissioned by Microsoft to develop this contribution. This link spurred controversy, some POI contributors questioning POI OOXML patent protection regarding Microsoft's Open Specification Promise patent license.
The Apache POI project contains the following subcomponents meaning of acronyms is taken from old documentation:
The HSSF component is the most advanced feature of the library. Other components HPSF, HWPF, and HSLF are usable, but less full-featured.
The POI library is also provided as a Ruby or ColdFusion extension.
There are modules for Big Data platforms e.g. Apache Hive/Apache Flink/Apache Spark, which provide certain functionality of Apache POI, such as the processing of Excel files.