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<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 APIs</title>

   <p>This HOW-TO is organized in three 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>
   </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 &lt; 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 &lt; 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 (Stichwörter)
      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><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>
  </section>
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</document>

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