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<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN"
"../dtd/document-v11.dtd">
<!-- $Id$ -->
<document>
<header>
<title>HPSF HOW-TO</title>
<authors>
<person name="Rainer Klute" email="klute@apache.org"/>
</authors>
</header>
<body>
<section><title>How To Use the HPSF API</title>
<p>This HOW-TO is organized in four sections. You should read them
sequentially because the later sections build upon the earlier ones.</p>
<ol>
<li>
The <link href="#sec1">first section</link> explains how to read
the most important standard properties of a Microsoft Office
document. Standard properties are things like title, author, creation
date etc. It is quite likely that you will find here what you need and
don't have to read the other sections.
</li>
<li>
The <link href="#sec2">second section</link> goes a small step
further and focusses on reading additional standard properties. It also
talks about exceptions that may be thrown when dealing with HPSF and
shows how you can read properties of embedded objects.
</li>
<li>
The <link href="#sec3">third section</link> tells how to read
non-standard properties. Non-standard properties are application-specific
triples consisting of an ID, a type, and a value.
</li>
<li>
The <link href="#sec4">fourth section</link> will tell you how to write
property set streams - once it is written. Writing is still quite
rudimentary in HPSF and you have to understand the <link
href="#sec3">third section</link> before you should think about writing
properties. Stick to the Javadoc API documentation to find out more about
writing property sets!
</li>
</ol>
<anchor id="sec1"/>
<section><title>Reading Standard Properties</title>
<note>This section explains how to read
the most important standard properties of a Microsoft Office
document. Standard properties are things like title, author, creation
date etc. Chances are that you will find here what you need and
don't have to read the other sections.</note>
<p>The first thing you should understand is that properties are stored in
separate documents inside the POI filesystem. (If you don't know what a
POI filesystem is, read the <link href="../poifs/index.html">POIFS
documentation</link>.) A document in a POI filesystem is also called a
<strong>stream</strong>.</p>
<p>The following example shows how to read a POI filesystem's
"title" property. Reading other properties is similar. Consider the API
documentation of <code>org.apache.poi.hpsf.SummaryInformation</code> to
learn which methods are available!</p>
<p>The standard properties this section focusses on can be found in a
document called <em>\005SummaryInformation</em> located in the root of the
POI filesystem. The notation <em>\005</em> in the document's name means
the character with the decimal value of 5. In order to read the title, an
application has to perform the following steps:</p>
<ol>
<li>
Open the document <em>\005SummaryInformation</em> located in the root
of the POI filesystem.
</li>
<li>
Create an instance of the class <code>SummaryInformation</code> from
that document.
</li>
<li>
Call the <code>SummaryInformation</code> instance's
<code>getTitle()</code> method.
</li>
</ol>
<p>Sounds easy, doesn't it? Here are the steps in detail.</p>
<section><title>Open the document \005SummaryInformation in the root of the
POI filesystem</title>
<p>An application that wants to open a document in a POI filesystem
(POIFS) proceeds as shown by the following code fragment. (The full
source code of the sample application is available in the
<em>examples</em> section of the POI source tree as
<em>ReadTitle.java</em>.</p>
<source>
import java.io.*;
import org.apache.poi.hpsf.*;
import org.apache.poi.poifs.eventfilesystem.*;
// ...
public static void main(String[] args)
throws IOException
{
final String filename = args[0];
POIFSReader r = new POIFSReader();
r.registerListener(new MyPOIFSReaderListener(),
"\005SummaryInformation");
r.read(new FileInputStream(filename));
}</source>
<p>The first interesting statement is</p>
<source>POIFSReader r = new POIFSReader();</source>
<p>It creates a
<code>org.apache.poi.poifs.eventfilesystem.POIFSReader</code> instance
which we shall need to read the POI filesystem. Before the application
actually opens the POI filesystem we have to tell the
<code>POIFSReader</code> which documents we are interested in. In this
case the application should do something with the document
<em>\005SummaryInformation</em>.</p>
<source>
r.registerListener(new MyPOIFSReaderListener(),
"\005SummaryInformation");</source>
<p>This method call registers a
<code>org.apache.poi.poifs.eventfilesystem.POIFSReaderListener</code>
with the <code>POIFSReader</code>. The <code>POIFSReaderListener</code>
interface specifies the method <code>processPOIFSReaderEvent</code>
which processes a document. The class
<code>MyPOIFSReaderListener</code> implements the
<code>POIFSReaderListener</code> and thus the
<code>processPOIFSReaderEvent</code> method. The eventing POI filesystem
calls this method when it finds the <em>\005SummaryInformation</em>
document. In the sample application <code>MyPOIFSReaderListener</code> is
a static class in the <em>ReadTitle.java</em> source file.</p>
<p>Now everything is prepared and reading the POI filesystem can
start:</p>
<source>r.read(new FileInputStream(filename));</source>
<p>The following source code fragment shows the
<code>MyPOIFSReaderListener</code> class and how it retrieves the
title.</p>
<source>
static class MyPOIFSReaderListener implements POIFSReaderListener
{
public void processPOIFSReaderEvent(POIFSReaderEvent event)
{
SummaryInformation si = null;
try
{
si = (SummaryInformation)
PropertySetFactory.create(event.getStream());
}
catch (Exception ex)
{
throw new RuntimeException
("Property set stream \"" +
event.getPath() + event.getName() + "\": " + ex);
}
final String title = si.getTitle();
if (title != null)
System.out.println("Title: \"" + title + "\"");
else
System.out.println("Document has no title.");
}
}
</source>
<p>The line</p>
<source>SummaryInformation si = null;</source>
<p>declares a <code>SummaryInformation</code> variable and initializes it
with <code>null</code>. We need an instance of this class to access the
title. The instance is created in a <code>try</code> block:</p>
<source>si = (SummaryInformation)
PropertySetFactory.create(event.getStream());</source>
<p>The expression <code>event.getStream()</code> returns the input stream
containing the bytes of the property set stream named
<em>\005SummaryInformation</em>. This stream is passed into the
<code>create</code> method of the factory class
<code>org.apache.poi.hpsf.PropertySetFactory</code> which returns
a <code>org.apache.poi.hpsf.PropertySet</code> instance. It is more or
less safe to cast this result to <code>SummaryInformation</code>, a
convenience class with methods like <code>getTitle()</code>,
<code>getAuthor()</code> etc.</p>
<p>The <code>PropertySetFactory.create</code> method may throw all sorts
of exceptions. We'll deal with them in the next sections. For now we just
catch all exceptions and throw a <code>RuntimeException</code>
containing the message text of the origin exception.</p>
<p>If all goes well, the sample application retrieves the title and prints
it to the standard output. As you can see you must be prepared for the
case that the POI filesystem does not have a title.</p>
<source>final String title = si.getTitle();
if (title != null)
System.out.println("Title: \"" + title + "\"");
else
System.out.println("Document has no title.");</source>
<p>Please note that a Microsoft Office document does not necessarily
contain the <em>\005SummaryInformation</em> stream. The documents created
by the Microsoft Office suite have one, as far as I know. However, an
Excel spreadsheet exported from StarOffice 5.2 won't have a
<em>\005SummaryInformation</em> stream. In this case the applications
won't throw an exception but simply does not call the
<code>processPOIFSReaderEvent</code> method. You have been warned!</p>
</section>
</section>
<anchor id="sec2"/>
<section><title>Additional Standard Properties, Exceptions And Embedded
Objects</title>
<note>This section focusses on reading additional standard properties. It
also talks about exceptions that may be thrown when dealing with HPSF and
shows how you can read properties of embedded objects.</note>
<p>A couple of <strong>additional standard properties</strong> are not
contained in the <em>\005SummaryInformation</em> stream explained above,
for example a document's category or the number of multimedia clips in a
PowerPoint presentation. Microsoft has invented an additional stream named
<em>\005DocumentSummaryInformation</em> to hold these properties. With two
minor exceptions you can proceed exactly as described above to read the
properties stored in <em>\005DocumentSummaryInformation</em>:</p>
<ul>
<li>Instead of <em>\005SummaryInformation</em> use
<em>\005DocumentSummaryInformation</em> as the stream's name.</li>
<li>Replace all occurrences of the class
<code>SummaryInformation</code> by
<code>DocumentSummaryInformation</code>.</li>
</ul>
<p>And of course you cannot call <code>getTitle()</code> because
<code>DocumentSummaryInformation</code> has different query methods. See
the Javadoc API documentation for the details!</p>
<p>In the previous section the application simply caught all
<strong>exceptions</strong> and was in no way interested in any
details. However, a real application will likely want to know what went
wrong and act appropriately. Besides any IO exceptions there are three
HPSF resp. POI specific exceptions you should know about:</p>
<dl>
<dt><code>NoPropertySetStreamException</code>:</dt>
<dd>
This exception is thrown if the application tries to create a
<code>PropertySet</code> instance from a stream that is not a
property set stream. (<code>SummaryInformation</code> and
<code>DocumentSummaryInformation</code> are subclasses of
<code>PropertySet</code>.) A faulty property set stream counts as not
being a property set stream at all. An application should be prepared to
deal with this case even if it opens streams named
<em>\005SummaryInformation</em> or
<em>\005DocumentSummaryInformation</em> only. These are just names. A
stream's name by itself does not ensure that the stream contains the
expected contents and that this contents is correct.
</dd>
<dt><code>UnexpectedPropertySetTypeException</code></dt>
<dd>This exception is thrown if a certain type of property set is
expected somewhere (e.g. a <code>SummaryInformation</code> or
<code>DocumentSummaryInformation</code>) but the provided property
set is not of that type.</dd>
<dt><code>MarkUnsupportedException</code></dt>
<dd>This exception is thrown if an input stream that is to be parsed
into a property set does not support the
<code>InputStream.mark(int)</code> operation. The POI filesystem uses
the <code>DocumentInputStream</code> class which does support this
operation, so you are safe here. However, if you read a property set
stream from another kind of input stream things may be
different.</dd>
</dl>
<p>Many Microsoft Office documents contain <strong>embedded
objects</strong>, for example an Excel sheet on a page in a Word
document. Embedded objects may have property sets of their own. An
application can open these property set streams as described above. The
only difference is that they are not located in the POI filesystem's root
but in a <strong>nested directory</strong> instead. Just register a
<code>POIFSReaderListener</code> for the property set streams you are
interested in. For example, the <em>POIBrowser</em> application in the
contrib section tries to open each and every document in a POI filesystem
as a property set stream. If this operation was successful it displays the
properties.</p>
</section>
<anchor id="sec3"/>
<section><title>Reading Non-Standard Properties</title>
<note>This section tells how to read non-standard properties. Non-standard
properties are application-specific ID/type/value triples.</note>
<section><title>Overview</title>
<p>Now comes the real hardcode stuff. As mentioned above,
<code>SummaryInformation</code> and
<code>DocumentSummaryInformation</code> are just special cases of the
general concept of a property set. This concept says that a
<strong>property set</strong> consists of properties and that each
<strong>property</strong> is an entity with an <strong>ID</strong>, a
<strong>type</strong>, and a <strong>value</strong>.</p>
<p>Okay, that was still rather easy. However, to make things more
complicated, Microsoft in its infinite wisdom decided that a property set
shalt be broken into one or more <strong>sections</strong>. Each section
holds a bunch of properties. But since that's still not complicated
enough, a section may have an optional <strong>dictionary</strong> that
maps property IDs to <strong>property names</strong> - we'll explain
later what that means.</p>
<p>The procedure to get to the properties is the following:</p>
<ol>
<li>Use the <strong><code>PropertySetFactory</code></strong> class to
create a <code>PropertySet</code> object from a property set stream. If
you don't know whether an input stream is a property set stream, just
try to call <code>PropertySetFactory.create(java.io.InputStream)</code>:
You'll either get a <code>PropertySet</code> instance returned or an
exception is thrown.</li>
<li>Call the <code>PropertySet</code>'s method <code>getSections()</code>
to get the sections contained in the property set. Each section is
an instance of the <code>Section</code> class.</li>
<li>Each section has a format ID. The format ID of the first section in a
property set determines the property set's type. For example, the first
(and only) section of the SummaryInformation property set has a format
ID of <code>F29F85E0-4FF9-1068-AB-91-08-00-2B-27-B3-D9</code>. You can
get the format ID with <code>Section.getFormatID()</code>.</li>
<li>The properties contained in a <code>Section</code> can be retrieved
with <code>Section.getProperties()</code>. The result is an array of
<code>Property</code> instances.</li>
<li>A property has a name, a type, and a value. The <code>Property</code>
class has methods to retrieve them.</li>
</ol>
</section>
<section><title>A Sample Application</title>
<p>Let's have a look at a sample Java application that dumps all property
set streams contained in a POI file system. The full source code of this
program can be found as <em>ReadCustomPropertySets.java</em> in the
<em>examples</em> area of the POI source code tree. Here are the key
sections:</p>
<source>import java.io.*;
import java.util.*;
import org.apache.poi.hpsf.*;
import org.apache.poi.poifs.eventfilesystem.*;
import org.apache.poi.util.HexDump;</source>
<p>The most important package the application needs is
<code>org.apache.poi.hpsf.*</code>. This package contains the HPSF
classes. Most classes named below are from the HPSF package. Of course we
also need the POIFS event file system's classes and <code>java.io.*</code>
since we are dealing with POI I/O. From the <code>java.util</code> package
we use the <code>List</code> and <code>Iterator</code> class. The class
<code>org.apache.poi.util.HexDump</code> provides a methods to dump byte
arrays as nicely formatted strings.</p>
<source>public static void main(String[] args)
throws IOException
{
final String filename = args[0];
POIFSReader r = new POIFSReader();
/* Register a listener for *all* documents. */
r.registerListener(new MyPOIFSReaderListener());
r.read(new FileInputStream(filename));
}</source>
<p>The <code>POIFSReader</code> is set up in a way that the listener
<code>MyPOIFSReaderListener</code> is called on every file in the POI file
system.</p>
</section>
<section><title>The Property Set</title>
<p>The listener class tries to create a <code>PropertySet</code> from each
stream using the <code>PropertySetFactory.create()</code> method:</p>
<source>static class MyPOIFSReaderListener implements POIFSReaderListener
{
public void processPOIFSReaderEvent(POIFSReaderEvent event)
{
PropertySet ps = null;
try
{
ps = PropertySetFactory.create(event.getStream());
}
catch (NoPropertySetStreamException ex)
{
out("No property set stream: \"" + event.getPath() +
event.getName() + "\"");
return;
}
catch (Exception ex)
{
throw new RuntimeException
("Property set stream \"" +
event.getPath() + event.getName() + "\": " + ex);
}
/* Print the name of the property set stream: */
out("Property set stream \"" + event.getPath() +
event.getName() + "\":");</source>
<p>Creating the <code>PropertySet</code> is done in a <code>try</code>
block, because not each stream in the POI file system contains a property
set. If it is some other file, the
<code>PropertySetFactory.create()</code> throws a
<code>NoPropertySetStreamException</code>, which is caught and
logged. Then the program continues with the next stream. However, all
other types of exceptions cause the program to terminate by throwing a
runtime exception. If all went well, we can print the name of the property
set stream.</p>
</section>
<section><title>The Sections</title>
<p>The next step is to print the number of sections followed by the
sections themselves:</p>
<source>/* Print the number of sections: */
final long sectionCount = ps.getSectionCount();
out(" No. of sections: " + sectionCount);
/* Print the list of sections: */
List sections = ps.getSections();
int nr = 0;
for (Iterator i = sections.iterator(); i.hasNext();)
{
/* Print a single section: */
Section sec = (Section) i.next();
// See below for the complete loop body.
}</source>
<p>The <code>PropertySet</code>'s method <code>getSectionCount()</code>
returns the number of sections.</p>
<p>To retrieve the sections, use the <code>getSections()</code>
method. This method returns a <code>java.util.List</code> containing
instances of the <code>Section</code> class in their proper order.</p>
<p>The sample code shows a loop that retrieves the <code>Section</code>
objects one by one and prints some information about each one. Here is
the complete body of the loop:</p>
<source>/* Print a single section: */
Section sec = (Section) i.next();
out(" Section " + nr++ + ":");
String s = hex(sec.getFormatID().getBytes());
s = s.substring(0, s.length() - 1);
out(" Format ID: " + s);
/* Print the number of properties in this section. */
int propertyCount = sec.getPropertyCount();
out(" No. of properties: " + propertyCount);
/* Print the properties: */
Property[] properties = sec.getProperties();
for (int i2 = 0; i2 < properties.length; i2++)
{
/* Print a single property: */
Property p = properties[i2];
int id = p.getID();
long type = p.getType();
Object value = p.getValue();
out(" Property ID: " + id + ", type: " + type +
", value: " + value);
}</source>
</section>
<section><title>The Section's Format ID</title>
<p>The first method called on the <code>Section</code> instance is
<code>getFormatID()</code>. As explained above, the format ID of the
first section in a property set determines the type of the property
set. Its type is <code>ClassID</code> which is essentially a sequence of
16 bytes. A real application using its own type of a custom property set
should have defined a unique format ID and, when reading a property set
stream, should check the format ID is equal to that unique format ID. The
sample program just prints the format ID it finds in a section:</p>
<source>String s = hex(sec.getFormatID().getBytes());
s = s.substring(0, s.length() - 1);
out(" Format ID: " + s);</source>
<p>As you can see, the <code>getFormatID()</code> method returns a
<code>ClassID</code> object. An array containing the bytes can be
retrieved with <code>ClassID.getBytes()</code>. In order to get a nicely
formatted printout, the sample program uses the <code>hex()</code> helper
method which in turn uses the POI utility class <code>HexDump</code> in
the <code>org.apache.poi.util</code> package. Another helper method is
<code>out()</code> which just saves typing
<code>System.out.println()</code>.</p>
</section>
<section><title>The Properties</title>
<p>Before getting the properties, it is possible to find out how many
properties are available in the section via the
<code>Section.getPropertyCount()</code>. The sample application uses this
method to print the number of properties to the standard output:</p>
<source>int propertyCount = sec.getPropertyCount();
out(" No. of properties: " + propertyCount);</source>
<p>Now its time to get to the properties themselves. You can retrieve a
section's properties with the method
<code>Section.getProperties()</code>:</p>
<source>Property[] properties = sec.getProperties();</source>
<p>As you can see the result is an array of <code>Property</code>
objects. This class has three methods to retrieve a property's ID, its
type, and its value. The following code snippet shows how to call
them:</p>
<source>for (int i2 = 0; i2 < properties.length; i2++)
{
/* Print a single property: */
Property p = properties[i2];
int id = p.getID();
long type = p.getType();
Object value = p.getValue();
out(" Property ID: " + id + ", type: " + type +
", value: " + value);
}</source>
</section>
<section><title>Sample Output</title>
<p>The output of the sample program might look like the following. It
shows the summary information and the document summary information
property sets of a Microsoft Word document. However, unlike the first and
second section of this HOW-TO the application does not have any code
which is specific to the <code>SummaryInformation</code> and
<code>DocumentSummaryInformation</code> classes.</p>
<source>Property set stream "/SummaryInformation":
No. of sections: 1
Section 0:
Format ID: 00000000 F2 9F 85 E0 4F F9 10 68 AB 91 08 00 2B 27 B3 D9 ....O..h....+'..
No. of properties: 17
Property ID: 1, type: 2, value: 1252
Property ID: 2, type: 30, value: Titel
Property ID: 3, type: 30, value: Thema
Property ID: 4, type: 30, value: Rainer Klute (Autor)
Property ID: 5, type: 30, value: Test (Stichw�rter)
Property ID: 6, type: 30, value: This is a document for testing HPSF
Property ID: 7, type: 30, value: Normal.dot
Property ID: 8, type: 30, value: Unknown User
Property ID: 9, type: 30, value: 3
Property ID: 18, type: 30, value: Microsoft Word 9.0
Property ID: 12, type: 64, value: Mon Jan 01 00:59:25 CET 1601
Property ID: 13, type: 64, value: Thu Jul 18 16:22:00 CEST 2002
Property ID: 14, type: 3, value: 1
Property ID: 15, type: 3, value: 20
Property ID: 16, type: 3, value: 93
Property ID: 19, type: 3, value: 0
Property ID: 17, type: 71, value: [B@13582d
Property set stream "/DocumentSummaryInformation":
No. of sections: 2
Section 0:
Format ID: 00000000 D5 CD D5 02 2E 9C 10 1B 93 97 08 00 2B 2C F9 AE ............+,..
No. of properties: 14
Property ID: 1, type: 2, value: 1252
Property ID: 2, type: 30, value: Test
Property ID: 14, type: 30, value: Rainer Klute (Manager)
Property ID: 15, type: 30, value: Rainer Klute IT-Consulting GmbH
Property ID: 5, type: 3, value: 3
Property ID: 6, type: 3, value: 2
Property ID: 17, type: 3, value: 111
Property ID: 23, type: 3, value: 592636
Property ID: 11, type: 11, value: false
Property ID: 16, type: 11, value: false
Property ID: 19, type: 11, value: false
Property ID: 22, type: 11, value: false
Property ID: 13, type: 4126, value: [B@56a499
Property ID: 12, type: 4108, value: [B@506411
Section 1:
Format ID: 00000000 D5 CD D5 05 2E 9C 10 1B 93 97 08 00 2B 2C F9 AE ............+,..
No. of properties: 7
Property ID: 0, type: 0, value: {6=Test-JaNein, 5=Test-Zahl, 4=Test-Datum, 3=Test-Text, 2=_PID_LINKBASE}
Property ID: 1, type: 2, value: 1252
Property ID: 2, type: 65, value: [B@c9ba38
Property ID: 3, type: 30, value: This is some text.
Property ID: 4, type: 64, value: Wed Jul 17 00:00:00 CEST 2002
Property ID: 5, type: 3, value: 27
Property ID: 6, type: 11, value: true
No property set stream: "/WordDocument"
No property set stream: "/CompObj"
No property set stream: "/1Table"</source>
<p>There are some interesting items to note:</p>
<ul>
<li>The first property set (summary information) consists of a single
section, the second property set (document summary information) consists
of two sections.</li>
<li>Each section type (identified by its format ID) has its own domain of
property ID. For example, in the second property set the properties with
ID 2 have different meanings in the two section. By the way, the format
IDs of these sections are <strong>not</strong> equal, but you have to
look hard to find the difference.</li>
<li>The properties are not in any particular order in the section,
although they slightly tend to be sorted by their IDs.</li>
</ul>
</section>
<section><title>Property IDs</title>
<p>Properties in the same section are distinguished by their IDs. This is
similar to variables in a programming language like Java, which are
distinguished by their names. But unlike variable names, property IDs are
simple integral numbers. There is another similarity, however. Just like
a Java variable has a certain scope (e.g. a member variables in a class),
a property ID also has its scope of validity: the section.</p>
<p>Two property IDs in sections with different section format IDs
don't have the same meaning even though their IDs might be equal. For
example, ID 4 in the first (and only) section of a summary
information property set denotes the document's author, while ID 4 in the
first section of the document summary information property set means the
document's byte count. The sample output above does not show a property
with an ID of 4 in the first section of the document summary information
property set. That means that the document does not have a byte
count. However, there is a property with an ID of 4 in the
<em>second</em> section: This is a user-defined property ID - we'll get
to that topic in a minute.</p>
<p>So, how can you find out what the meaning of a certain property ID in
the summary information and the document summary information property set
is? The standard property sets as such don't have any hints about the
<strong>meanings of their property IDs</strong>. For example, the summary
information property set does not tell you that the property ID 4 stands
for the document's author. This is external knowledge. Microsoft defined
standard meanings for some of the property IDs in the summary information
and the document summary information property sets. As a help to the Java
and POI programmer, the class <code>PropertyIDMap</code> in the
<code>org.apache.poi.hpsf.wellknown</code> package defines constants
for the "well-known" property IDs. For example, there is the
definition</p>
<source>public final static int PID_AUTHOR = 4;</source>
<p>These definitions allow you to use symbolic names instead of
numbers.</p>
<p>In order to provide support for the other way, too, - i.e. to map
property IDs to property names - the class <code>PropertyIDMap</code>
defines two static methods:
<code>getSummaryInformationProperties()</code> and
<code>getDocumentSummaryInformationProperties()</code>. Both return
<code>java.util.Map</code> objects which map property IDs to
strings. Such a string gives a hint about the property's meaning. For
example,
<code>PropertyIDMap.getSummaryInformationProperties().get(4)</code>
returns the string "PID_AUTHOR". An application could use this string as
a key to a localized string which is displayed to the user, e.g. "Author"
in English or "Verfasser" in German. HPSF might provide such
language-dependend ("localized") mappings in a later release.</p>
<p>Usually you won't have to deal with those two maps. Instead you should
call the <code>Section.getPIDString(int)</code> method. It returns the
string associated with the specified property ID in the context of the
<code>Section</code> object.</p>
<p>Above you learned that property IDs have a meaning in the scope of a
section only. However, there are two exceptions to the rule: The property
IDs 0 and 1 have a fixed meaning in <strong>all</strong> sections:</p>
<table>
<tr>
<th>Property ID</th>
<th>Meaning</th>
</tr>
<tr>
<td>0</td>
<td>The property's value is a <strong>dictionary</strong>, i.e. a
mapping from property IDs to strings.</td>
</tr>
<tr>
<td>1</td>
<td>The property's value is the number of a <strong>codepage</strong>,
i.e. a mapping from character codes to characters. All strings in the
section containing this property must be interpreted using this
codepage. Typical property values are 1252 (8-bit "western" characters)
or 1200 (16-bit Unicode characters).</td>
</tr>
</table>
</section>
<section><title>Property types</title>
<p>A property is nothing without its value. It is stored in a property set
stream as a sequence of bytes. You must know the property's
<strong>type</strong> in order to properly interpret those bytes and
reasonably handle the value. A property's type is one of the so-called
Microsoft-defined <strong>"variant types"</strong>. When you call
<code>Property.getType()</code> you'll get a <code>long</code> value
which denoting the property's variant type. The class
<code>Variant</code> in the <code>org.apache.poi.hpsf</code> package
holds most of those <code>long</code> values as named constants. For
example, the constant <code>VT_I4 = 3</code> means a signed integer value
of four bytes. Examples of other types are <code>VT_LPSTR = 30</code>
meaning a null-terminated string of 8-bit characters, <code>VT_LPWSTR =
31</code> which means a null-terminated Unicode string, or <code>VT_BOOL
= 11</code> denoting a boolean value.</p>
<p>In most cases you won't need a property's type because HPSF does all
the work for you.</p>
</section>
<section><title>Property values</title>
<p>When an application wants to retrieve a property's value and calls
<code>Property.getValue()</code>, HPSF has to interpret the bytes making
out the value according to the property's type. The type determines how
many bytes the value consists of and what
to do with them. For example, if the type is <code>VT_I4</code>, HPSF
knows that the value is four bytes long and that these bytes
comprise a signed integer value in the little-endian format. This is
quite different from e.g. a type of <code>VT_LPWSTR</code>. In this case
HPSF has to scan the value bytes for a Unicode null character and collect
everything from the beginning to that null character as a Unicode
string.</p>
<p>The good new is that HPSF does another job for you, too: It maps the
variant type to an adequate Java type.</p>
<table>
<tr>
<th>Variant type:</th>
<th>Java type:</th>
</tr>
<tr>
<td>VT_I2</td>
<td>java.lang.Integer</td>
</tr>
<tr>
<td>VT_I4</td>
<td>java.lang.Long</td>
</tr>
<tr>
<td>VT_FILETIME</td>
<td>java.util.Date</td>
</tr>
<tr>
<td>VT_LPSTR</td>
<td>java.lang.String</td>
</tr>
<tr>
<td>VT_LPWSTR</td>
<td>java.lang.String</td>
</tr>
<tr>
<td>VT_CF</td>
<td>byte[]</td>
</tr>
<tr>
<td>VT_BOOL</td>
<td>java.lang.Boolean</td>
</tr>
</table>
<p>The bad news is that there are still a couple of variant types HPSF
does not yet support. If it encounters one of these types it
returns the property's value as a byte array and leaves it to be
interpreted by the application.</p>
<p>An application retrieves a property's value by calling the
<code>Property.getValue()</code> method. This method's return type is the
abstract <code>Object</code> class. The <code>getValue()</code> method
looks up the property's variant type, reads the property's value bytes,
creates an instance of an adequate Java type, assigns it the property's
value and returns it. Primitive types like <code>int</code> or
<code>long</code> will be returned as the corresponding class,
e.g. <code>Integer</code> or <code>Long</code>.</p>
</section>
<section><title>Dictionaries</title>
<p>The property with ID 0 has a very special meaning: It is a
<strong>dictionary</strong> mapping property IDs to property names. We
have seen already that the meanings of standard properties in the
summary information and the document summary information property sets
have been defined by Microsoft. The advantage is that the labels of
properties like "Author" or "Title" don't have to be stored in the
property set. However, a user can define custom fields in, say, Microsoft
Word. For each field the user has to specify a name, a type, and a
value.</p>
<p>The names of the custom-defined fields (i.e. the property names) are
stored in the document summary information second section's
<strong>dictionary</strong>. The dictionary is a map which associates
property IDs with property names.</p>
<p>The method <code>Section.getPIDString(int)</code> not only returns with
the well-known property names of the summary information and document
summary information property sets, but with self-defined properties,
too. It should also work with self-defined properties in self-defined
sections.</p>
</section>
<section><title>Codepage support</title>
<fixme author="Rainer Klute">Improve codepage support!</fixme>
<p>The property with ID 1 holds the number of the codepage which was used
to encode the strings in this section. The present HPSF codepage support
is still very limited: When reading property value strings, HPSF
distinguishes between 16-bit characters and 8-bit characters. 16-bit
characters should be Unicode characters and thus be okay. 8-bit
characters are interpreted according to the platform's default character
set. This is fine as long as the document being read has been written on
a platform with the same default character set. However, if you receive a
document from another region of the world and want to process it with
HPSF you are in trouble - unless the creator used Unicode, of course.</p>
</section>
</section>
<anchor id="sec4"/>
<section><title>Writing Properties</title>
<note>This section describes how to write properties.</note>
<section><title>Overview</title>
<p>Writing properties is possible at a low level only at the moment. You
have to deal with property IDs and variant types to write
properties. There are no convenient classes or convenient methods for
dealing with summary information and document summary information streams
yet. If you have not already done so, you should read <link
href="#sec3">section 3</link> to understand the following.</p>
<p>HPSF's writing capabilities come with the classes
<code>MutablePropertySet</code>, <code>MutableSection</code>, and
<code>MutableProperty</code> and some helper classes. The "mutable"
classes extend their superclasses <code>PropertySet</code>,
<code>Section</code>, and <code>Property</code> and provide "set" and
"write" methods.</p>
<p>When you are going to write a property set stream your application has
to perform the following steps:</p>
<ol>
<li>Create a <code>MutablePropertySet</code> instance.</li>
<li>Get hold of a <code>MutableSection</code>. You can either retrieve
the one that is always present in a new <code>MutablePropertySet</code>
or create a new <code>MutableSection</code> and add it to the
<code>MutablePropertySet</code>.
</li>
<li>Set any <code>Section</code> fields as you like.</li>
<li>Create as many <code>MutableProperty</code> objects as you need. Set
each property's ID, type, and value. Add the
<code>MutableProperties</code> to the <code>MutableSection</code>.
</li>
<li>Create further <code>MutableSection</code>s if you need them.</li>
<li>Eventually retrieve the property set as a byte stream using
<code>MutablePropertySet.toInputStream()</code> and write it to a POIFS
document.</li>
</ol>
</section>
<section><title>Low-level Writing Functions In Details</title>
<fixme author="Rainer Klute">This section is still to be written.</fixme>
</section>
</section>
<section><title>Further Reading</title>
<p>There are still some aspects of HSPF left which are not covered by this
HOW-TO. You should dig into the Javadoc API documentation to learn
further details. Since you've struggled through this document up to this
point, you are well prepared.</p>
</section>
</section>
</body>
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