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--><!-- $Id: embedding.xml 1298724 2012-03-09 07:55:31Z cbowditch $ --><!-- Embedding FOP --><!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.3//EN" "document-v13.dtd">
<document xmlns:xi="http://www.w3.org/2001/XInclude">
  <header>
    <title>Apache&#8482; FOP: Embedding</title>
    <subtitle>How to Embed FOP in a Java application</subtitle>
    <version>$Revision: 1298724 $</version>
  </header>

  <body>
  <section id="overview">
    <title>Overview</title>
    <p>
      Review <link href="running.html">Running Apache&#8482; FOP</link> for important information that applies
      to embedded applications as well as command-line use, such as options and performance.
    </p>
    <p>
      To embed Apache&#8482; FOP in your application, first create a new
      org.apache.fop.apps.FopFactory instance. This object can be used to launch multiple
      rendering runs. For each run, create a new org.apache.fop.apps.Fop instance through
      one of the factory methods of FopFactory. In the method call you specify which output
      format (i.e. MIME type) to use and, if the selected output format requires an
      OutputStream, which OutputStream to use for the results of the rendering. You can
      customize FOP's behaviour in a rendering run by supplying your own FOUserAgent
      instance. The FOUserAgent can, for example, be used to set your own document handler
      instance (details below). Finally, you retrieve a SAX DefaultHandler instance from
      the Fop object and use that as the SAXResult of your transformation.
    </p>
  </section>
  <section id="API">
    <title>The API</title>
    <p>
      FOP has many classes which express the "public" access modifier, however, this is not
      indicative of their inclusion into the public API. Every attempt will be made to keep the
      public API static, to minimize regressions for existing users, however, since the API is not
      clearly defined, the list of classes below are the generally agreed public API:
      <source xml:space="preserve"><![CDATA[
org.apache.fop.apps.*
org.apache.fop.fo.FOEventHandler
org.apache.fop.fo.ElementMappingRegistry
org.apache.fop.fonts.FontManager
org.apache.fop.events.EventListener
org.apache.fop.events.Event
org.apache.fop.events.model.EventSeverity
org.apache.fop.render.ImageHandlerRegistry
org.apache.fop.render.RendererFactory
org.apache.fop.render.intermediate.IFContext
org.apache.fop.render.intermediate.IFDocumentHandler
org.apache.fop.render.intermediate.IFException
org.apache.fop.render.intermediate.IFParser
org.apache.fop.render.intermediate.IFSerializer
org.apache.fop.render.intermediate.IFUtil
org.apache.fop.render.intermediate.util.IFConcatenator]]></source>
    </p>
  </section>
  <section id="basics">
    <title>Basic Usage Pattern</title>
    <p>
      Apache FOP relies heavily on JAXP. It uses SAX events exclusively to receive the XSL-FO
      input document. It is therefore a good idea that you know a few things about JAXP (which
      is a good skill anyway). Let's look at the basic usage pattern for FOP...
    </p>
    <p>Here is the basic pattern to render an XSL-FO file to PDF:
    </p>
    <source xml:space="preserve"><![CDATA[
import org.apache.fop.apps.FopFactory;
import org.apache.fop.apps.Fop;
import org.apache.fop.apps.MimeConstants;

/*..*/

// Step 1: Construct a FopFactory
// (reuse if you plan to render multiple documents!)
FopFactory fopFactory = FopFactory.newInstance();

// Step 2: Set up output stream.
// Note: Using BufferedOutputStream for performance reasons (helpful with FileOutputStreams).
OutputStream out = new BufferedOutputStream(new FileOutputStream(new File("C:/Temp/myfile.pdf")));

try {
  // Step 3: Construct fop with desired output format
  Fop fop = fopFactory.newFop(MimeConstants.MIME_PDF, out);

  // Step 4: Setup JAXP using identity transformer
  TransformerFactory factory = TransformerFactory.newInstance();
  Transformer transformer = factory.newTransformer(); // identity transformer

  // Step 5: Setup input and output for XSLT transformation
  // Setup input stream
  Source src = new StreamSource(new File("C:/Temp/myfile.fo"));

  // Resulting SAX events (the generated FO) must be piped through to FOP
  Result res = new SAXResult(fop.getDefaultHandler());

  // Step 6: Start XSLT transformation and FOP processing
  transformer.transform(src, res);

} finally {
  //Clean-up
  out.close();
}]]></source>
    <p>
      Let's discuss these 5 steps in detail:
    </p>
    <ul>
      <li>
        <strong>Step 1:</strong> You create a new FopFactory instance. The FopFactory instance holds
        references to configuration information and cached data. It's important to reuse this
        instance if you plan to render multiple documents during a JVM's lifetime.
      </li>
      <li>
        <strong>Step 2:</strong> You set up an OutputStream that the generated document
        will be written to. It's a good idea to buffer the OutputStream as demonstrated
        to improve performance.
      </li>
      <li>
        <strong>Step 3:</strong> You create a new Fop instance through one of the factory
        methods on the FopFactory. You tell the FopFactory what your desired output format
        is. This is done by using the MIME type of the desired output format (ex. "application/pdf").
        You can use one of the MimeConstants.* constants. The second parameter is the
        OutputStream you've setup up in step 2.
      </li>
      <li>
        <strong>Step 4</strong> We recommend that you use JAXP Transformers even
        if you don't do XSLT transformations to generate the XSL-FO file. This way
        you can always use the same basic pattern. The example here sets up an
        "identity transformer" which just passes the input (Source) unchanged to the
        output (Result). You don't have to work with a SAXParser if you don't do any
        XSLT transformations.
      </li>
      <li>
        <strong>Step 5:</strong> Here you set up the input and output for the XSLT
        transformation. The Source object is set up to load the "myfile.fo" file.
        The Result is set up so the output of the XSLT transformation is sent to FOP.
        The FO file is sent to FOP in the form of SAX events which is the most efficient
        way. Please always avoid saving intermediate results to a file or a memory buffer
        because that affects performance negatively.
      </li>
      <li>
        <strong>Step 6:</strong> Finally, we start the XSLT transformation by starting
        the JAXP Transformer. As soon as the JAXP Transformer starts to send its output
        to FOP, FOP itself starts its processing in the background. When the
        <code>transform()</code> method returns FOP will also have finished converting
        the FO file to a PDF file and you can close the OutputStream.
        <note label="Tip!">
          It's a good idea to enclose the whole conversion in a try..finally statement. If
          you close the OutputStream in the finally section, this will make sure that the
          OutputStream is properly closed even if an exception occurs during the conversion.
        </note>
      </li>
    </ul>
    <p>
      If you're not totally familiar with JAXP Transformers, please have a look at the
      <link href="#examples">Embedding examples</link> below. The section contains examples
      for all sorts of use cases. If you look at all of them in turn you should be able
      to see the patterns in use and the flexibility this approach offers without adding
      too much complexity.
    </p>
    <p>
      This may look complicated at first, but it's really just the combination of an
      XSL transformation and a FOP run. It's also easy to comment out the FOP part
      for debugging purposes, for example when you're tracking down a bug in your
      stylesheet. You can easily write the XSL-FO output from the XSL transformation
      to a file to check if that part generates the expected output. An example for that
      can be found in the <link href="#examples">Embedding examples</link> (See "ExampleXML2FO").
    </p>
    <section id="basic-logging">
      <title>Logging</title>
      <p>
        Logging is now a little different than it was in FOP 0.20.5. We've switched from
        Avalon Logging to <link href="ext:commons-logging">Jakarta Commons Logging</link>.
        While with Avalon Logging the loggers were directly given to FOP, FOP now retrieves
        its logger(s) through a statically available LogFactory. This is similar to the
        general pattern that you use when you work with Apache Log4J directly, for example.
        We call this "static logging" (Commons Logging, Log4J) as opposed to "instance logging"
        (Avalon Logging). This has a consequence: You can't give FOP a logger for each
        processing run anymore. The log output of multiple, simultaneously running FOP instances
        is sent to the same logger.
      </p>
      <p>
        By default, <link href="ext:commons-logging">Jakarta Commons Logging</link> uses
        JDK logging (available in JDKs 1.4 or higher) as its backend. You can configure Commons
        Logging to use an alternative backend, for example Log4J. Please consult the
        <link href="ext:commons-logging">documentation for Jakarta Commons Logging</link> on
        how to configure alternative backends.
      </p>
      <p>
        As a result of the above we differentiate between two kinds of "logging":
      </p>
      <ul>
        <li>(FOP-)Developer-oriented logging</li>
        <li><link href="events.html">User/Integrator-oriented feedback</link> (NEW!)</li>
      </ul>
      <p>
        The use of "feedback" instead of "logging" is intentional. Most people were using
        log output as a means to get feedback from events within FOP. Therefore, FOP now
        includes an <code>event</code> package which can be used to receive feedback from
        the layout engine and other components within FOP <strong>per rendering run</strong>.
        This feedback is not just some
        text but event objects with parameters so these events can be interpreted by code.
        Of course, there is a facility to turn these events into normal human-readable
        messages. For details, please read on on the <link href="events.html">Events page</link>.
        This leaves normal logging to be mostly a thing used by the FOP developers
        although anyone can surely activate certain logging categories but the feedback
        from the loggers won't be separated by processing runs. If this is required,
        the <link href="events.html">Events subsystem</link> is the right approach.
      </p>
    </section>

    <section id="render">
      <title>Processing XSL-FO</title>
      <p>
        Once the Fop instance is set up, call <code>getDefaultHandler()</code> to obtain a SAX
        DefaultHandler instance to which you can send the SAX events making up the XSL-FO
        document you'd like to render. FOP processing starts as soon as the DefaultHandler's
        <code>startDocument()</code> method is called. Processing stops again when the
        DefaultHandler's <code>endDocument()</code> method is called. Please refer to the basic
        usage pattern shown above to render a simple XSL-FO document.
      </p>
    </section>

    <section id="render-with-xslt">
      <title>Processing XSL-FO generated from XML+XSLT</title>
      <p>
        If you want to process XSL-FO generated from XML using XSLT we recommend
        again using standard JAXP to do the XSLT part and piping the generated SAX
        events directly through to FOP. The only thing you'd change to do that
        on the basic usage pattern above is to set up the Transformer differently:
      </p>
      <source xml:space="preserve"><![CDATA[
  //without XSLT:
  //Transformer transformer = factory.newTransformer(); // identity transformer

  //with XSLT:
  Source xslt = new StreamSource(new File("mystylesheet.xsl"));
  Transformer transformer = factory.newTransformer(xslt);]]></source>
    </section>
  </section>
  <section id="input">
    <title>Input Sources</title>
    <p>
      The input XSL-FO document is always received by FOP as a SAX stream (see the
      <link href="../dev/design/parsing.html">Parsing Design Document</link> for the rationale).
    </p>
    <p>
      However, you may not always have your input document available as a SAX stream.
      But with JAXP it's easy to convert different input sources to a SAX stream so you
      can pipe it into FOP. That sounds more difficult than it is. You simply have
      to set up the right Source instance as input for the JAXP transformation.
      A few examples:
    </p>
    <ul>
      <li>
        <strong>URL:</strong> <code>Source src = new StreamSource("http://localhost:8080/testfile.xml");</code>
      </li>
      <li>
        <strong>File:</strong> <code>Source src = new StreamSource(new File("C:/Temp/myinputfile.xml"));</code>
      </li>
      <li>
        <strong>String:</strong> <code>Source src = new StreamSource(new StringReader(myString)); // myString is a String</code>
      </li>
      <li>
        <strong>InputStream:</strong> <code>Source src = new StreamSource(new MyInputStream(something));</code>
      </li>
      <li>
        <strong>Byte Array:</strong> <code>Source src = new StreamSource(new ByteArrayInputStream(myBuffer)); // myBuffer is a byte[] here</code>
      </li>
      <li>
        <strong>DOM:</strong> <code>Source src = new DOMSource(myDocument); // myDocument is a Document or a Node</code>
      </li>
      <li>
        <strong>Java Objects:</strong> Please have a look at the <link href="#examples">Embedding examples</link> which contain an example for this.
      </li>
    </ul>
    <p>
      There are a variety of upstream data manipulations possible.
      For example, you may have a DOM and an XSL stylesheet; or you may want to
      set variables in the stylesheet. Interface documentation and some cookbook
      solutions to these situations are provided in
      <link href="http://xml.apache.org/xalan-j/usagepatterns.html">Xalan Basic Usage Patterns</link>.
    </p>
  </section>
  <section id="config-internal">
    <title>Configuring Apache FOP Programmatically</title>
    <p>
      Apache FOP provides two levels on which you can customize FOP's
      behaviour: the FopFactory and the user agent.
    </p>
    <section id="fop-factory">
      <title>Customizing the FopFactory</title>
      <p>
        The FopFactory holds configuration data and references to objects which are reusable over
        multiple rendering runs. It's important to instantiate it only once (except in special
        environments) and reuse it every time to create new FOUserAgent and Fop instances.
      </p>
      <p>
        You can set all sorts of things on the FopFactory:
      </p>
      <ul>
        <li>
          <p>
            The <strong>font base URL</strong> to use when resolving relative URLs for fonts. Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.getFontManager().setFontBaseURL("file:///C:/Temp/fonts");]]></source>
        </li>
        <li>
          <p>
            The <strong>hyphenation base URL</strong> to use when resolving relative URLs for
            hyphenation patterns. Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.setHyphenBaseURL("file:///C:/Temp/hyph");]]></source>
        </li>
        <li>
          <p>
            Disable <strong>strict validation</strong>. When disabled FOP is less strict about the rules
            established by the XSL-FO specification. Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.setStrictValidation(false);]]></source>
        </li>
        <li>
          <p>
            Enable an <strong>alternative set of rules for text indents</strong> that tries to mimic the behaviour of many commercial
            FO implementations, that chose to break the specification in this respect. The default of this option is
            'false', which causes Apache FOP to behave exactly as described in the specification. To enable the
            alternative behaviour, call:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.setBreakIndentInheritanceOnReferenceAreaBoundary(true);]]></source>
        </li>
        <li>
          <p>
            Set the <strong>source resolution</strong> for the document. This is used internally to determine the pixel
            size for SVG images and bitmap images without resolution information. Default: 72 dpi. Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.setSourceResolution(96); // =96dpi (dots/pixels per Inch)]]></source>
        </li>
        <li>
          <p>
            Manually add an <strong>ElementMapping instance</strong>. If you want to supply a special FOP extension
            you can give the instance to the FOUserAgent. Normally, the FOP extensions can be automatically detected
            (see the documentation on extension for more info). Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.addElementMapping(myElementMapping); // myElementMapping is a org.apache.fop.fo.ElementMapping]]></source>
        </li>
        <li>
          <p>
            Set a <strong>URIResolver</strong> for custom URI resolution. By supplying a JAXP URIResolver you can add
            custom URI resolution functionality to FOP. For example, you can use
            <link href="ext:xml.apache.org/commons/resolver">Apache XML Commons Resolver</link> to make use of XCatalogs. Example:
          </p>
          <source xml:space="preserve"><![CDATA[fopFactory.setURIResolver(myResolver); // myResolver is a javax.xml.transform.URIResolver]]></source>
          <note>
            Both the FopFactory and the FOUserAgent have a method to set a URIResolver. The URIResolver on the FopFactory
            is primarily used to resolve URIs on factory-level (hyphenation patterns, for example) and it is always used
            if no other URIResolver (for example on the FOUserAgent) resolved the URI first.
          </note>
        </li>
      </ul>
    </section>
    <section id="user-agent">
      <title>Customizing the User Agent</title>
      <p>
        The user agent is the entity that allows you to interact with a single rendering run, i.e. the processing of a single
        document. If you wish to customize the user agent's behaviour, the first step is to create your own instance
        of FOUserAgent using the appropriate factory method on FopFactory and pass that
        to the factory method that will create a new Fop instance:
      </p>
      <source xml:space="preserve"><![CDATA[
  FopFactory fopFactory = FopFactory.newInstance(); // Reuse the FopFactory if possible!
  // do the following for each new rendering run
  FOUserAgent userAgent = fopFactory.newFOUserAgent();
  // customize userAgent
  Fop fop = fopFactory.newFop(MimeConstants.MIME_POSTSCRIPT, userAgent, out);]]></source>
      <p>
        You can do all sorts of things on the user agent:
      </p>
      <ul>
        <li>
          <p>
            The <strong>base URL</strong> to use when resolving relative URLs. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setBaseURL("file:///C:/Temp/");]]></source>
        </li>
        <li>
          <p>
            Set the <strong>producer</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. The default producer is "Apache FOP". Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setProducer("MyKillerApplication");]]></source>
        </li>
        <li>
          <p>
            Set the <strong>creating user</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setCreator("John Doe");]]></source>
        </li>
        <li>
          <p>
            Set the <strong>author</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setAuthor("John Doe");]]></source>
        </li>
        <li>
          <p>
            Override the <strong>creation date and time</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setCreationDate(new Date());]]></source>
        </li>
        <li>
          <p>
            Set the <strong>title</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setTitle("Invoice No 138716847");]]></source>
        </li>
        <li>
          <p>
            Set the <strong>keywords</strong> of the document. This is metadata information that can be used for certain output formats such as PDF. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setKeywords("XML XSL-FO");]]></source>
        </li>
        <li>
          <p>
            Set the <strong>target resolution</strong> for the document. This is used to
            specify the output resolution for bitmap images generated by bitmap renderers
            (such as the TIFF renderer) and by bitmaps generated by Apache Batik for filter
            effects and such. Default: 72 dpi. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setTargetResolution(300); // =300dpi (dots/pixels per Inch)]]></source>
        </li>
        <li>
          <p>
            Set <strong>your own Document Handler</strong>. This feature can be used for several purposes, the most likey usage of which would probably be
            binding a MIME type when the output is Intermediate Format (see <link href="#documenthandlers">Document Handlers</link>). This also allows advanced
            users to create their own implementation of the document handler.
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setDocumentHandlerOverride(documentHandler) // documentHandler is an instance of org.apache.fop.render.intermediate.IFDocumentHandler]]></source>
        </li>
        <li>
          <p>
            Set <strong>your own FOEventHandler instance</strong>. If you want to supply your own FOEventHandler or
            configure an FOEventHandler subclass in a special way you can give the instance to the FOUserAgent. Normally,
            the FOEventHandler instance is created by FOP. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setFOEventHandlerOverride(myFOEventHandler); // myFOEventHandler is an org.apache.fop.fo.FOEventHandler]]></source>
        </li>
        <li>
          <p>
            Set a <strong>URIResolver</strong> for custom URI resolution. By supplying a JAXP URIResolver you can add
            custom URI resolution functionality to FOP. For example, you can use
            <link href="ext:xml.apache.org/commons/resolver">Apache XML Commons Resolver</link> to make use of XCatalogs. Example:
          </p>
          <source xml:space="preserve"><![CDATA[userAgent.setURIResolver(myResolver); // myResolver is a javax.xml.transform.URIResolver]]></source>
          <note>
            Both the FopFactory and the FOUserAgent have a method to set a URIResolver. The URIResolver on the FOUserAgent is
            used for resolving URIs which are document-related. If it's not set or cannot resolve a URI, the URIResolver
            from the FopFactory is used.
          </note>
        </li>
      </ul>
      <note>
        You should not reuse an FOUserAgent instance between FOP rendering runs although you can. Especially
        in multi-threaded environment, this is a bad idea.
      </note>
    </section>
  </section>
  <section id="config-external">
    <title>Using a Configuration File</title>
    <p>
      Instead of setting the parameters manually in code as shown above you can also set
      many values from an XML configuration file:
    </p>
    <source xml:space="preserve"><![CDATA[
import org.apache.avalon.framework.configuration.Configuration;
import org.apache.avalon.framework.configuration.DefaultConfigurationBuilder;

/*..*/

DefaultConfigurationBuilder cfgBuilder = new DefaultConfigurationBuilder();
Configuration cfg = cfgBuilder.buildFromFile(new File("C:/Temp/mycfg.xml"));
fopFactory.setUserConfig(cfg);

/* ..or.. */

fopFactory.setUserConfig(new File("C:/Temp/mycfg.xml"));]]></source>
    <p>
      The layout of the configuration file is described on the <link href="configuration.html">Configuration page</link>.
    </p>
  </section>
  <section id="documenthandlers">
    <title>Document Handlers</title>
    <p>
      The document handlers are classes that inherit from <code>org.apache.fop.render.intermediate.IFDocumentHandler</code>. This
      is an interface for which a MIME type specific implementation can be created. This same handler is used either when XSL-FO
      is used as the input or when Intermediate Format is used. Since IF is output format agnostic, if custom fonts or other
      configuration information that affect layout (specific to a particular MIME type) are given then FOP needs that contextual
      information. The document handler provides that context so that when the IF is rendered, it is more visually consistent with
      FO rendering. The code below shows an example of how a document handler can be used to provide PDF configuration data to the
      IFSerializer.
      <source xml:space="preserve"><![CDATA[
IFDocumentHandler targetHandler = userAgent.getRendererFactory().createDocumentHandler(userAgent, MimeConstants.MIME_PDF);

IFSerializer ifSerializer = new IFSerializer();  //Create the IFSerializer to write the intermediate format
ifSerializer.setContext(new IFContext(userAgent));
ifSerializer.mimicDocumentHandler(targetHandler);   //Tell the IFSerializer to mimic the target format

userAgent.setDocumentHandlerOverride(ifSerializer);  //Make sure the prepared document handler is used
      ]]></source>
      The rest of the code is the same as in <link href="#basics">Basic Usage Patterns</link>. 
    </p>
  </section>
  <section id="hints">
    <title>Hints</title>
    <section id="object-reuse">
      <title>Object reuse</title>
      <p>
        Fop instances shouldn't (and can't) be reused. Please recreate
        Fop and FOUserAgent instances for each rendering run using the FopFactory.
        This is a cheap operation as all reusable information is held in the
        FopFactory. That's why it's so important to reuse the FopFactory instance.
     </p>
    </section>
    <section id="awt">
      <title>AWT issues</title>
      <p>
        If your XSL-FO files contain SVG then Apache Batik will be used. When Batik is
        initialised it uses certain classes in <code>java.awt</code> that
        intialise the Java AWT classes. This means that a daemon thread
        is created by the JVM and on Unix it will need to connect to a
        DISPLAY.
      </p>
      <p>
        The thread means that the Java application may not automatically quit
        when finished, you will need to call <code>System.exit()</code>. These
        issues should be fixed in the JDK 1.4.
      </p>
      <p>
        If you run into trouble running FOP on a head-less server, please see the
        <link href="graphics.html#batik">notes on Batik</link>.
      </p>
    </section>
    <section id="render-info">
      <title>Getting information on the rendering process</title>
      <p>
        To get the number of pages that were rendered by FOP you can call
        <code>Fop.getResults()</code>. This returns a <code>FormattingResults</code> object
        where you can look up the number of pages produced. It also gives you the
        page-sequences that were produced along with their id attribute and their
        numbers of pages. This is particularly useful if you render multiple
        documents (each enclosed by a page-sequence) and have to know the number of
        pages of each document.
      </p>
    </section>
  </section>
  <section id="performance">
    <title>Improving performance</title>
    <p>
      There are several options to consider:
    </p>
    <ul>
      <li>
        Whenever possible, try to use SAX to couple the individual components involved
        (parser, XSL transformer, SQL datasource etc.).
      </li>
      <li>
        Depending on the target OutputStream (in case of a FileOutputStream, but not
        for a ByteArrayOutputStream, for example) it may improve performance considerably
        if you buffer the OutputStream using a BufferedOutputStream:
        <code>out = new java.io.BufferedOutputStream(out);</code>
        <br/>
        Make sure you properly close the OutputStream when FOP is finished.
      </li>
      <li>
        Cache the stylesheet. If you use the same stylesheet multiple times
        you can set up a JAXP <code>Templates</code> object and reuse it each time you do
        the XSL transformation.  (More information can be found
        <link class="fork" href="http://www.javaworld.com/javaworld/jw-05-2003/jw-0502-xsl.html">here</link>.)
      </li>
      <li>
        Use an XSLT compiler like <link class="fork" href="http://xml.apache.org/xalan-j/xsltc_usage.html">XSLTC</link>
        that comes with Xalan-J.
      </li>
      <li>
        Fine-tune your stylesheet to make the XSLT process more efficient and to create XSL-FO that can
        be processed by FOP more efficiently. Less is more: Try to make use of property inheritance where possible.
      </li>
      <li>
        You may also wish to consider trying to reduce <link href="http://xmlgraphics.apache.org/fop/trunk/running.html#memory">memory usage</link>.
      </li>
    </ul>
  </section>
  <section id="multithreading">
    <title>Multithreading FOP</title>
    <p>
      Apache FOP may currently not be completely thread safe.
      The code has not been fully tested for multi-threading issues, yet.
      If you encounter any suspicious behaviour, please notify us.
    </p>
    <p>
      There is also a known issue with fonts being jumbled between threads when using
      the Java2D/AWT renderer (which is used by the -awt and -print output options).
      In general, you cannot safely run multiple threads through the AWT renderer.
    </p>
  </section>
<section id="examples">
  <title>Examples</title>
  <p>
   The directory "{fop-dir}/examples/embedding" contains several working examples.
  </p>
  <section id="ExampleFO2PDF">
    <title>ExampleFO2PDF.java</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleFO2PDF.java?view=markup">
            example</link>
demonstrates the basic usage pattern to transform an XSL-FO
file to PDF using FOP.
    </p>
    <figure src="images/EmbeddingExampleFO2PDF.png" alt="Example XSL-FO to PDF"/>
  </section>
  <section id="ExampleXML2FO">
    <title>ExampleXML2FO.java</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleXML2FO.java?view=markup">
            example</link>
has nothing to do with FOP. It is there to show you how an XML
file can be converted to XSL-FO using XSLT. The JAXP API is used to do the
transformation. Make sure you've got a JAXP-compliant XSLT processor in your
classpath (ex. <link href="http://xml.apache.org/xalan-j">Xalan</link>).
    </p>
    <figure src="images/EmbeddingExampleXML2FO.png" alt="Example XML to XSL-FO"/>
  </section>
  <section id="ExampleXML2PDF">
    <title>ExampleXML2PDF.java</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleXML2PDF.java?view=markup">
        example</link>
demonstrates how you can convert an arbitrary XML file to PDF
using XSLT and XSL-FO/FOP. It is a combination of the first two examples
above. The example uses JAXP to transform the XML file to XSL-FO and FOP to
transform the XSL-FO to PDF.
    </p>
    <figure src="images/EmbeddingExampleXML2PDF.png" alt="Example XML to PDF (via XSL-FO)"/>
    <p>
The output (XSL-FO) from the XSL transformation is piped through to FOP using
SAX events. This is the most efficient way to do this because the
intermediate result doesn't have to be saved somewhere. Often, novice users
save the intermediate result in a file, a byte array or a DOM tree. We
strongly discourage you to do this if it isn't absolutely necessary. The
performance is significantly higher with SAX.
    </p>
  </section>
  <section id="ExampleObj2XML">
    <title>ExampleObj2XML.java</title>
    <p>This
    <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleObj2XML.java?view=markup">
        example</link>
is a preparatory example for the next one. It's an example that
shows how an arbitrary Java object can be converted to XML. It's an often
needed task to do this. Often people create a DOM tree from a Java object and
use that. This is pretty straightforward. The example here, however, shows how
to do this using SAX, which will probably be faster and not even more
complicated once you know how this works.
    </p>
    <figure src="images/EmbeddingExampleObj2XML.png" alt="Example Java object to XML"/>
    <p>
For this example we've created two classes: ProjectTeam and ProjectMember
(found in xml-fop/examples/embedding/java/embedding/model). They represent
the same data structure found in
xml-fop/examples/embedding/xml/xml/projectteam.xml. We want to serialize to XML a
project team with several members which exist as Java objects.
Therefore we created the two classes: ProjectTeamInputSource and
ProjectTeamXMLReader (in the same place as ProjectTeam above).
    </p>
    <p>
The XMLReader implementation (regard it as a special kind of XML parser) is
responsible for creating SAX events from the Java object. The InputSource
class is only used to hold the ProjectTeam object to be used.
    </p>
    <p>
Have a look at the source of ExampleObj2XML.java to find out how this is
used. For more detailed information see other resources on JAXP (ex.
<link class="fork" href="http://java.sun.com/xml/jaxp/dist/1.1/docs/tutorial/xslt/3_generate.html">An older JAXP tutorial</link>).
    </p>
  </section>
  <section id="ExampleObj2PDF">
    <title>ExampleObj2PDF.java</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleObj2PDF.java?view=markup">
            example</link>
combines the previous and the third to demonstrate
how you can transform a Java object to a PDF directly in one smooth run
by generating SAX events from the Java object that get fed to an XSL
transformation. The result of the transformation is then converted to PDF
using FOP as before.
    </p>
    <figure src="images/EmbeddingExampleObj2PDF.png" alt="Example Java object to PDF (via XML and XSL-FO)"/>
  </section>
  <section id="ExampleDOM2PDF">
    <title>ExampleDOM2PDF.java</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleDOM2PDF.java?view=markup">
            example</link>
has FOP use a DOMSource instead of a StreamSource in order to
use a DOM tree as input for an XSL transformation.
    </p>
  </section>
  <section id="ExampleSVG2PDF">
    <title>ExampleSVG2PDF.java (PDF Transcoder example)</title>
    <p>This
        <link href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/ExampleSVG2PDF.java?view=markup">
            example</link>
shows the usage of the PDF Transcoder, a sub-application within FOP.
It is used to generate a PDF document from an SVG file.
    </p>
  </section>
  <section id="ExampleConcat">
    <title>ExampleConcat.java (IF Concatenation example)</title>
    <p>
This can be found in the <code>embedding.intermediate</code> package within the
examples and describes how IF can be concatenated to produce a document. Because
IF has been through FOPs layout engine, it should be visually consistent with FO
rendered documents while allowing the user to merge numerous documents together.
    </p>
  </section>
  <section id="example-notes">
    <title>Final notes</title>
    <p>
These examples should give you an idea of what's possible. It should be easy
to adjust these examples to your needs. Also, if you have other examples that you
think should be added here, please let us know via either the fop-users or fop-dev
mailing lists.  Finally, for more help please send your questions to the fop-users
mailing list.
    </p>
  </section>
</section>
  </body>
</document>