Packages
org.apache.poi  
org.apache.poi.common.usermodel  
org.apache.poi.common.usermodel.fonts  
org.apache.poi.ddf This package contains classes for decoding the Microsoft Office Drawing format otherwise known as escher henceforth known in POI as the Dreadful Drawing Format.
org.apache.poi.dev  
org.apache.poi.extractor  
org.apache.poi.hpsf
org.apache.poi.hpsf.extractor  
org.apache.poi.hpsf.wellknown
Specific support for DocumentSummaryInformation, SummaryInformation types.
org.apache.poi.hssf Horrible SpreadSheet Format API's for reading/writting Excel files using pure Java.
org.apache.poi.hssf.dev DEV package serves two purposes.
org.apache.poi.hssf.eventmodel  
org.apache.poi.hssf.eventusermodel HSSF eventmodel Package provides an event-based API for reading HSSF files.
org.apache.poi.hssf.eventusermodel.dummyrecord  
org.apache.poi.hssf.extractor  
org.apache.poi.hssf.model Provides low level API structures for reading, writing, modifying XLS files.
org.apache.poi.hssf.record Record package contains class representations for XLS binary strutures.
org.apache.poi.hssf.record.aggregates record aggregates are not real "records" but collections of records that act as a single record.
org.apache.poi.hssf.record.cf  
org.apache.poi.hssf.record.chart  
org.apache.poi.hssf.record.common  
org.apache.poi.hssf.record.cont  
org.apache.poi.hssf.record.crypto  
org.apache.poi.hssf.record.pivottable  
org.apache.poi.hssf.usermodel usermodel package maps HSSF low level strutures to familiar workbook/sheet model
org.apache.poi.hssf.usermodel.helpers  
org.apache.poi.hssf.util util package contains tools needed for writing HSSF files that are not necesarily "real" HSSF concepts.
org.apache.poi.poifs.common common package contains constants and other classes shared across all POIFS subpackages
org.apache.poi.poifs.crypt Implementation of the ECMA-376 Document Encryption
org.apache.poi.poifs.crypt.binaryrc4  
org.apache.poi.poifs.crypt.cryptoapi  
org.apache.poi.poifs.crypt.standard  
org.apache.poi.poifs.crypt.xor  
org.apache.poi.poifs.dev DEV package serves two purposes.
org.apache.poi.poifs.eventfilesystem The eventfilesystem is an efficient method for reading OLE 2 CDF files.
org.apache.poi.poifs.filesystem filesystem package maps OLE 2 Compound document files to a more familiar filesystem interface.
org.apache.poi.poifs.macros  
org.apache.poi.poifs.nio  
org.apache.poi.poifs.property property package contains high and low level Property structures for POIFS.
org.apache.poi.poifs.storage storage package contains low level binary structures for POIFS's implementation of the OLE 2 Compound Document Format.
org.apache.poi.sl.draw  
org.apache.poi.sl.draw.binding  
org.apache.poi.sl.draw.geom  
org.apache.poi.sl.image  
org.apache.poi.sl.usermodel  
org.apache.poi.ss  
org.apache.poi.ss.extractor  
org.apache.poi.ss.format This package contains classes that implement cell formatting
org.apache.poi.ss.formula This package contains common internal POI code for manipulating formulas.
org.apache.poi.ss.formula.atp  
org.apache.poi.ss.formula.constant  
org.apache.poi.ss.formula.eval  
org.apache.poi.ss.formula.eval.forked  
org.apache.poi.ss.formula.function  
org.apache.poi.ss.formula.functions  
org.apache.poi.ss.formula.ptg formula package contains binary PTG structures used in Formulas
org.apache.poi.ss.formula.udf  
org.apache.poi.ss.usermodel  
org.apache.poi.ss.usermodel.charts  
org.apache.poi.ss.usermodel.helpers  
org.apache.poi.ss.util  
org.apache.poi.ss.util.cellwalk  
org.apache.poi.util Top-level util package are classes that are useful throughout the project.
org.apache.poi.wp.usermodel