Processes streams in the Horrible Property Set Format (HPSF) in POI filesystems. Microsoft Office documents, i.e. POI filesystems, usually contain meta data like author, title, last saving time etc. These items are called properties and stored in property set streams along with the document itself. These streams are commonly named `\005SummaryInformation` and `\005DocumentSummaryInformation`. However, a POI filesystem may contain further property sets of other names or types.

In order to extract the properties from a POI filesystem, a property set stream's contents must be parsed into a {@link org.apache.poi.hpsf.PropertySet} instance. Its subclasses {@link org.apache.poi.hpsf.SummaryInformation} and {@link org.apache.poi.hpsf.DocumentSummaryInformation} deal with the well-known property set streams `\005SummaryInformation` and `\005DocumentSummaryInformation`. (However, the streams' names are irrelevant. What counts is the property set's first section's format ID - see below.)

The factory method {@link org.apache.poi.hpsf.PropertySetFactory#create} creates a {@link org.apache.poi.hpsf.PropertySet} instance. This method always returns the most specific property set: If it identifies the stream data as a Summary Information or as a Document Summary Information it returns an instance of the corresponding class, else the general {@link org.apache.poi.hpsf.PropertySet}.

A {@link org.apache.poi.hpsf.PropertySet} contains a list of {@link org.apache.poi.hpsf.Section}s which can be retrieved with {@link org.apache.poi.hpsf.PropertySet#getSections}. Each {@link org.apache.poi.hpsf.Section} contains a {@link org.apache.poi.hpsf.Property} array which can be retrieved with {@link org.apache.poi.hpsf.Section#getProperties}. Since the vast majority of {@link org.apache.poi.hpsf.PropertySet}s contains only a single {@link org.apache.poi.hpsf.Section}, the convenience method {@link org.apache.poi.hpsf.PropertySet#getProperties} returns the properties of a {@link org.apache.poi.hpsf.PropertySet}'s {@link org.apache.poi.hpsf.Section} (throwing a {@link org.apache.poi.hpsf.NoSingleSectionException} if the {@link org.apache.poi.hpsf.PropertySet} contains more (or less) than exactly one {@link org.apache.poi.hpsf.Section}).

Each {@link org.apache.poi.hpsf.Property} has an ID, a type, and a value which can be retrieved with {@link org.apache.poi.hpsf.Property#getID}, {@link org.apache.poi.hpsf.Property#getType}, and {@link org.apache.poi.hpsf.Property#getValue}, respectively. The value's class depends on the property's type. The current implementation does not yet support all property types and restricts the values' classes to {@link java.lang.String}, {@link java.lang.Integer} and {@link java.util.Date}. A value of a yet unknown type is returned as a byte array containing the value's origin bytes from the property set stream.

To retrieve the value of a specific {@link org.apache.poi.hpsf.Property}, use {@link org.apache.poi.hpsf.Section#getProperty} or {@link org.apache.poi.hpsf.Section#getPropertyIntValue}.

The {@link org.apache.poi.hpsf.SummaryInformation} and {@link org.apache.poi.hpsf.DocumentSummaryInformation} classes provide convenience methods for retrieving well-known properties. For example, an application that wants to retrieve a document's title string just calls {@link org.apache.poi.hpsf.SummaryInformation#getTitle} instead of going through the hassle of first finding out what the title's property ID is and then using this ID to get the property's value.

Public documentation from Microsoft can be found in the appropriate section of the MSDN Library.

## History

2003-09-11:

  {@link org.apache.poi.hpsf.PropertySetFactory#create(InputStream)} no longer throws an {@link org.apache.poi.hpsf.UnexpectedPropertySetTypeException}.

## To Do

The following is still left to be implemented. Sponsering could foster these issues considerably.

- Convenience methods for setting summary information and document summary information properties

- Better codepage support

- Support for more property (variant) types

@author Rainer Klute (klute@rainer-klute.de)