More HPSF property writing documentation.
git-svn-id: https://svn.apache.org/repos/asf/jakarta/poi/trunk@353351 13f79535-47bb-0310-9956-ffa450edef68
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Rainer Klute
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@ -39,12 +39,11 @@
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</li>
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<li>
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The <link href="#sec4">fourth section</link> will tell you how to write
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property set streams - once it is written. Writing is still quite
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rudimentary in HPSF and you have to understand the <link
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href="#sec3">third section</link> before you should think about writing
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properties. Stick to the Javadoc API documentation to find out more about
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writing property sets!
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The <link href="#sec4">fourth section</link> tells you how to write
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property set streams. Writing is still rudimentary in HPSF. You have to
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understand the <link href="#sec3">third section</link> before you should
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think about writing properties. Check the Javadoc API documentation to
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find out about the details!
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</li>
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</ol>
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@ -347,7 +346,7 @@ else
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<li>Each section has a format ID. The format ID of the first section in a
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property set determines the property set's type. For example, the first
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(and only) section of the SummaryInformation property set has a format
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(and only) section of the summary information property set has a format
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ID of <code>F29F85E0-4FF9-1068-AB-91-08-00-2B-27-B3-D9</code>. You can
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get the format ID with <code>Section.getFormatID()</code>.</li>
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@ -854,18 +853,18 @@ No property set stream: "/1Table"</source>
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<note>This section describes how to write properties.</note>
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<section><title>Overview</title>
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<section><title>Overview of Writing Properties</title>
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<p>Writing properties is possible at a low level only at the moment. You
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have to deal with property IDs and variant types to write
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properties. There are no convenient classes or convenient methods for
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properties. There are no convenience classes or convenience methods for
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dealing with summary information and document summary information streams
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yet. If you have not already done so, you should read <link
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href="#sec3">section 3</link> to understand the following.</p>
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yet. Therefore you should have read <link href="#sec3">section 3</link>
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to understand what follows in this section.</p>
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<p>HPSF's writing capabilities come with the classes
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<code>MutablePropertySet</code>, <code>MutableSection</code>, and
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<code>MutableProperty</code> and some helper classes. The "mutable"
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classes extend their superclasses <code>PropertySet</code>,
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<code>MutablePropertySet</code>, <code>MutableSection</code>,
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<code>MutableProperty</code>, and some helper classes. The "mutable"
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classes extend their respective superclasses <code>PropertySet</code>,
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<code>Section</code>, and <code>Property</code> and provide "set" and
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"write" methods.</p>
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@ -876,16 +875,17 @@ No property set stream: "/1Table"</source>
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<li>Create a <code>MutablePropertySet</code> instance.</li>
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<li>Get hold of a <code>MutableSection</code>. You can either retrieve
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the one that is always present in a new <code>MutablePropertySet</code>
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or create a new <code>MutableSection</code> and add it to the
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<code>MutablePropertySet</code>.
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the one that is always present in a new <code>MutablePropertySet</code>,
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or you have to create a new <code>MutableSection</code> and add it to
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the <code>MutablePropertySet</code>.
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</li>
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<li>Set any <code>Section</code> fields as you like.</li>
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<li>Create as many <code>MutableProperty</code> objects as you need. Set
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each property's ID, type, and value. Add the
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<code>MutableProperties</code> to the <code>MutableSection</code>.
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<code>MutableProperty</code> objects to the
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<code>MutableSection</code>.
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</li>
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<li>Create further <code>MutableSection</code>s if you need them.</li>
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@ -897,10 +897,190 @@ No property set stream: "/1Table"</source>
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</section>
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<section><title>Low-level Writing Functions In Details</title>
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<fixme author="Rainer Klute">This section is still to be written.</fixme>
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<p>Writing properties is introduced by an artificial but simple example: a
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program creating a new document (aka POI file system) which contains only
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a single document: a summary information property set stream. The latter
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will hold the document's title only. This is artificial in that it does
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not contain any Word, Excel or other kind of useful application document
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data. A document containing just a property set is without any practical
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use. However, is makes the example very simple, and you will get quickly
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used to writing properties.</p>
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<p>Here's the source code of the sample application. You can also find it
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in the "examples" section of the POI source code
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distribution. Explanations are following below.</p>
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<source>package org.apache.poi.hpsf.examples;
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import java.io.*;
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import org.apache.poi.hpsf.*;
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import org.apache.poi.hpsf.wellknown.*;
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import org.apache.poi.poifs.filesystem.*;
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public class WriteTitle
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{
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public static void main(final String[] args)
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throws WritingNotSupportedException, IOException
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{
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/* Check whether we have exactly one command-line argument. */
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if (args.length != 1)
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{
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System.err.println("Usage: " + WriteTitle.class.getName() +
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"destinationPOIFS");
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System.exit(1);
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}
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final String fileName = args[0];
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final POIFSFileSystem poiFs = new POIFSFileSystem();
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/* Create a mutable property set. Initially it contains a single section
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* with no properties. */
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final MutablePropertySet mps = new MutablePropertySet();
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/* Retrieve the section the property set already contains. */
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final MutableSection ms = (MutableSection) mps.getSections().get(0);
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/* Turn the property set into a summary information property. This is
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* done by setting the format ID of its first section to
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* SectionIDMap.SUMMARY_INFORMATION_ID. */
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ms.setFormatID(SectionIDMap.SUMMARY_INFORMATION_ID);
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/* Create an empty property. */
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final MutableProperty p = new MutableProperty();
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/* Fill the property with appropriate settings so that it specifies the
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* document's title. */
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p.setID(PropertyIDMap.PID_TITLE);
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p.setType(Variant.VT_LPWSTR);
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p.setValue("Sample title");
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/* For writing the property set into a POI file system it has to be
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* handed over to the POIFS.createDocument() method as an input stream
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* which produces the bytes making out the property set stream. */
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final InputStream is = mps.toInputStream();
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/* Create the summary information property set in the POI file
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* system. It is given the default name most (if not all) summary
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* information property sets have. */
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poiFs.createDocument(is, SummaryInformation.DEFAULT_STREAM_NAME);
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/* Write the whole POI file system to a disk file. */
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poiFs.writeFilesystem(new FileOutputStream(fileName));
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}
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}</source>
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<p>The application expects the name of the POI file system to be created
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on the command line. It checks that there is exactly a single argument
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and stores it in the <code>fileName</code> variable:</p>
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<source>if (args.length != 1)
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{
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System.err.println("Usage: " + WriteTitle.class.getName() +
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"destinationPOIFS");
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System.exit(1);
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}
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final String fileName = args[0];</source>
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<p>Let's create a property set now. We cannot use the
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<code>PropertySet</code> class, because it is read-only: It does not have
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a constructor creating an empty property set, and it does not have any
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methods to modify its contents. Instead use the class
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<code>MutablePropertySet</code>. It is a subclass of
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<code>PropertySet</code>, and its no-args constructor established an
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empty property set which we will fill later.</p>
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<source>final MutablePropertySet mps = new MutablePropertySet();</source>
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<p>By the way, the <code>MutablePropertySet</code> class has another
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constructor taking a <code>PropertySet</code> as parameter. It creates a
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mutable copy of its parameter.</p>
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<p>The <code>MutablePropertySet</code> created by the no-args constructor
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is not really empty: It contains a single section without any
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properties. We can either retrieve that section and fill it with
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properties, or we can replace it by another section. Of course we can
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also add further sections to the property set. The sample application
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decides to retrieve the section being already there:</p>
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<source>final MutableSection ms = (MutableSection) mps.getSections().get(0);</source>
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<p>The <code>getSections()</code> method returns the property set's
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sections as a list, i.e. an instance of
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<code>java.util.List</code>. Calling <code>get(0)</code> returns the
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list's first (or zeroth if you prefer) element. It is a
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<code>MutableSection</code>: a subclass of <code>Section</code> you can
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modify.</p>
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<p>Presently the <code>MutableSection</code> is still empty: It contains
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no properties and does not have a format ID. As you have read in <link
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href="#sec3">above</link> the format ID of the first section in a
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property set determines the property set's type. If our property set
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should become a summary information property set we have to set the
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format ID of its first (and only) section to
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<code>F29F85E0-4FF9-1068-AB-91-08-00-2B-27-B3-D9</code>. However, you
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won't have to remember that ID if you want to write your own
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summary information property sets: HPSF has it defined as the well-known
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constant <code>Section.getFormatID()</code>. The sample application
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writes it to the section with the <code>setFormatID(byte[])</code>
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method.</p>
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<source>ms.setFormatID(SectionIDMap.SUMMARY_INFORMATION_ID);</source>
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<p>Now it is time to create a property. As you might expect there is a
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subclass of <code>Property</code> called
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<code>MutableProperty</code>.</p>
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<source>final MutableProperty p = new MutableProperty();</source>
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<p>A <code>MutableProperty</code> object must have an ID, a type, and a
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value (see <link href="#sec3">above</link> for details). The class
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provides methods to set these attributes:</p>
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<source>p.setID(PropertyIDMap.PID_TITLE);
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p.setType(Variant.VT_LPWSTR);
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p.setValue("Sample title");</source>
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<p>Now the sample property set is complete: We have a
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<code>MutablePropertySet</code> containing a <code>MutableSection</code>
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containing a <code>MutableProperty</code>. Of course we could have added
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more sections and properties but we wanted to keep things simple.</p>
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<p>The property set has to be written to a POI file system. The following
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statement creates it.</p>
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<source>final POIFSFileSystem poiFs = new POIFSFileSystem();</source>
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<p>In order to write the property set to a POI file system it must be
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converted into a sequence of bytes. The <code>MutablePropertySet</code>
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class has a method <code>toInputStream()</code>. This method returns an
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<code>InputStream</code> containing the bytes making out the property set
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stream.</p>
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<source>final InputStream is = mps.toInputStream();</source>
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<p>If you'd read from this input stream you'd receive all these
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bytes. However, it is very likely that you never do that. Instead you'll
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pass the input stream to the <code>createDocument()</code> method of a
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<code>POIFSFileSystem</code> instance, like the one we created a few
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lines ago. Besides an <code>InputStream</code> the
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<code>createDocument()</code> method takes another parameter: the name of
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the document to be created. For a summary information property set stream
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the default name is available as
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<code>SummaryInformation.DEFAULT_STREAM_NAME</code>:</p>
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<source>poiFs.createDocument(is, SummaryInformation.DEFAULT_STREAM_NAME);</source>
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<p>The last step is to write the POI file system to a disk file:</p>
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<source>poiFs.writeFilesystem(new FileOutputStream(fileName));</source>
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</section>
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</section>
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<section><title>Further Reading</title>
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<p>There are still some aspects of HSPF left which are not covered by this
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HOW-TO. You should dig into the Javadoc API documentation to learn
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