Apache POI - Architecture

Architecture

The Apache POI project contains the following subcomponents:

• POIFS (Poor Obfuscation Implementation File System) – This component reads and writes Microsoft's OLE 2 Compound document format. Since all Microsoft Office files are OLE 2 files, this component is the basic building block of all the other POI elements. POIFS can therefore be used to read a wider variety of files, beyond those whose explicit decoders are already written in POI.
• HSSF (Horrible SpreadSheet Format) – reads and writes Microsoft Excel (XLS) format files. It can read files written by Excel 97 onwards; this file format is known as the BIFF 8 format. As the Excel file format is complex and contains a number of tricky characteristics, some of the more advanced features cannot be read.
• XSSF (XML SpreadSheet Format) – reads and writes Office Open XML (XLSX) format files. Similar feature set to HSSF, but for Office Open XML files.
• HPSF (Horrible Property Set Format) – reads "Document Summary" information from Microsoft Office files. This is essentially the information that one can see by using the File|Properties menu item within an Office application.
• HWPF (Horrible Word Processor Format) – aims to read and write Microsoft Word 97 (DOC) format files. This component is in initial stages of development.
• HSLF (Horrible Slide Layout Format) – a pure Java implementation for Microsoft PowerPoint files. This provides the ability to read, create and edit presentations (though some things are easier to do than others)
• HDGF (Horrible DiaGram Format) – an initial pure Java implementation for Microsoft Visio binary files. It provides an ability to read the low level contents of the files.
• HPBF (Horrible PuBlisher Format) – a pure Java implementation for Microsoft Publisher files.
• HSMF (Horrible Stupid Mail Format) – a pure Java implementation for Microsoft Outlook MSG files.
• DDF (Dreadful Drawing Format) – a package for decoding the Microsoft Office Drawing format.

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.