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<?xml version="1.0" standalone="no"?>
<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.1//EN"
"http://cvs.apache.org/viewcvs.cgi/*checkout*/xml-forrest/src/resources/schema/dtd/document-v11.dtd">
<!-- Embedding FOP -->
<document>
<header>
<title>Embedding FOP</title>
<subtitle>How to Embed FOP in a Java application</subtitle>
</header>
<body>
<section id="overview">
<title>Overview</title>
<p>Review <link href="running.html">Running 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 FOP in your application, instantiate org.apache.fop.apps.Driver.
Once this class is
instantiated, methods are called to set the
Renderer to use
and the OutputStream to use to output the results of the
rendering (where applicable). In the case of the Renderer and
ElementMapping(s), the Driver may be supplied either with the
object itself, or the name of the class, in which case Driver will
instantiate the class itself. The advantage of the latter is it
enables runtime determination of Renderer and ElementMapping(s).
</p>
</section>
<section id="basics">
<title>Basics</title>
<p>The simplest way to use Driver is to instantiate it with the
InputSource and OutputStream, then set the renderer desired and
call the run method.
</p>
<p>Here is an example use of Driver which outputs PDF:
</p>
<source><![CDATA[
import org.apache.fop.apps.Driver;
/*..*/
Driver driver = new Driver(new InputSource(args[0]),
new FileOutputStream(args[1]));
driver.setRenderer(Driver.RENDER_PDF);
driver.run();]]></source>
<p>
In the example above, args[0] contains the path to an XSL-FO file, while
args[1] contains a path for the target PDF file.
</p>
<section id="basic-logging">
<title>Logging</title>
<p>
You also need to set up logging. Global logging for all FOP
processes is managed by MessageHandler. Per-instance logging
is handled by Driver. You want to set both using an implementation
of org.apache.avalon.framework.logger.Logger. See
<jump href="#logging">below</jump> for more information.
</p>
<p>
Call <code>setLogger(Logger)</code> always immediately after
instantiating the Driver object. See here:
</p>
<source><![CDATA[
import org.apache.avalon.framework.logger.Logger;
import org.apache.avalon.framework.logger.ConsoleLogger;
/*..*/
Driver driver = new Driver();
Logger logger = new ConsoleLogger(ConsoleLogger.LEVEL_INFO);
MessageHandler.setScreenLogger(logger);
driver.setLogger(logger);]]></source>
</section>
<section id="render">
<title>Processing XSL-FO</title>
<p>
Once the Driver is set up, one of the <code>render()</code> methods
is called. Depending on whether DOM or an InputSource is being used, the
invocation of the method is either <code>render(Document)</code> or
<code>render(Parser, InputSource)</code> respectively.
</p>
<p>
<strong>Another possibility may be used to build the FO Tree: You can
call <code>getContentHandler()</code> and fire the SAX events yourself.
</strong>
You don't have to call <code>run()</code> or <code>render()</code> on the
Driver object if you use <code>getContentHandler()</code>.
</p>
<p>Here is an example use of Driver:</p>
<source><![CDATA[
Driver driver = new Driver();
//Setup logging here: driver.setLogger(...
driver.setRenderer(Driver.RENDER_PDF);
driver.setInputSource(new FileInputSource(args[0]));
driver.setOutputStream(new FileOutputStream(args[1]));
driver.run();]]></source>
</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
using standard JAXP to do the XSLT part and piping the generated SAX
events directly through to FOP. Here's how this would look like:
</p>
<source><![CDATA[
Driver driver = new Driver();
//Setup logging here: driver.setLogger(...
driver.setRenderer(Driver.RENDER_PDF);
//Setup the OutputStream for FOP
driver.setOutputStream(new java.io.FileOutputStream(outFile));
//Make sure the XSL transformation's result is piped through to FOP
Result res = new SAXResult(driver.getContentHandler());
//Setup XML input
Source src = new StreamSource(xmlFile);
//Setup Transformer
Source xsltSrc = new StreamSource(xslFile);
TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer(xsltSrc);
//Start the transformation and rendering process
transformer.transform(src, res);]]></source>
<note>There's no need to call <code>run()</code> or <code>render()</code>.</note>
<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.
</p>
<p>
For fully working examples of the above and hints to some interesting
possibilities, see the <link href="#examples">examples section</link> below.
</p>
</section>
</section>
<section id="logging">
<title>Controlling logging</title>
<p>
FOP uses the
<fork href="http://avalon.apache.org/framework/api/org/apache/avalon/framework/logger/package-summary.html">Logger package</fork>
from Apache Avalon Framework to do logging. See the
<fork href="http://avalon.apache.org/framework/">Apache Avalon Framework</fork>
for more information.
</p>
<p>
Per default FOP uses the ConsoleLogger which logs to System.out. If you want to do logging using a
logging framework (such as LogKit, Log4J or JDK 1.4 Logging) you can set a
different Logger implementation on the Driver object. Here's an example how you would use LogKit:
</p>
<source><![CDATA[
Hierarchy hierarchy = Hierarchy.getDefaultHierarchy();
PatternFormatter formatter = new PatternFormatter(
"[%{priority}]: %{message}\n%{throwable}" );
LogTarget target = null;
target = new StreamTarget(System.out, formatter);
hierarchy.setDefaultLogTarget(target);
log = hierarchy.getLoggerFor("fop");
log.setPriority(Priority.INFO);
driver.setLogger(new org.apache.avalon.framework.logger.LogKitLogger(log));]]></source>
<p>
The LogKitLogger class implements the Logger interface so all logging calls are being redirected to LogKit.
More information on Jakarta LogKit can be found <fork href="http://jakarta.apache.org/avalon/logkit/index.html">here</fork>.
</p>
<p>
Similar implementations exist for Log4J (org.apache.avalon.framework.logger.Log4JLogger) and
JDK 1.4 logging (org.apache.avalon.framework.logger.Jdk14Logger).
</p>
<p>
If you want FOP to be totally silent you can also set an org.apache.avalon.framework.logger.NullLogger instance.
</p>
<p>
If you want to use yet another logging facility you simply have to create a class that
implements org.apache.avalon.framework.logging.Logger and set it on the Driver object.
See the existing implementations in Avalon Framework for examples.
</p>
</section>
<section id="input">
<title>Input Sources</title>
<p>
The input XSL-FO document is always handled internally as SAX (see the
<link href="design/parsing.html">Parsing Design Document</link> for the rationale).
However, the input itself can be provided in a variety of ways to FOP,
which normalizes the input (if necessary) into SAX events:
</p>
<ul>
<li><strong>SAX Events through SAX Handler</strong>: <code>FOTreeBuilder</code> is the SAX Handler which is obtained through <code>getContentHandler</code> on <code>Driver</code>.</li>
<li><strong>DOM (which is converted into SAX Events)</strong>: The conversion of a DOM tree is done via the <code>render(Document)</code> method on <code>Driver</code>.</li>
<li><strong>Data Source (which is parsed and converted into SAX Events)</strong>: The <code>Driver</code> can take an <code>InputSource</code> as input.
This can use a <code>Stream</code>, <code>String</code> etc.</li>
<li><strong>XML+XSLT Transformation</strong> (which is transformed using an XSLT Processor and the result is fired as SAX Events: <code>XSLTInputHandler</code> is used as an <code>InputSource</code> in the render(<code>XMLReader</code>, <code>InputSource</code>) method on <code>Driver</code>.</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
<fork href="http://xml.apache.org/xalan-j/usagepatterns.html">Xalan Basic Usage Patterns</fork>.
</p>
<p>
See the <link href="#examples">Examples</link> for some variations on input.
</p>
</section>
<section id="config-external">
<title>Using a Configuration File</title>
<p>
To access an external configuration:
</p>
<source><![CDATA[
import org.apache.fop.apps.Options;
/*..*/
userConfigFile = new File(userConfig);
options = new Options(userConfigFile);]]></source>
<note>
This is all you need to do, it sets up a static configuration class.
</note>
<p>
No further reference to the <code>options</code> variable is necessary.
The "options = " is actually not even necessary.
</p>
<p>
See <link href="#multithreading">Multithreading FOP</link> for issues related to changing configuration in a multithreaded environment.
</p>
</section>
<section id="config-internal">
<title>Setting the Configuration Programmatically</title>
<p>
If you wish to set configuration options from within your embedded application, use the <code>Configuration.put</code> method. Here is an example that sets the "baseDir" configuration in a Unix environment:
</p>
<source>org.apache.fop.configuration.Configuration.put("baseDir","/my/base/dir");</source>
<p>
Here is another that sets baseDir in a Windows environment:
</p>
<source>org.apache.fop.configuration.Configuration.put("baseDir","C:\my\base\dir");</source>
<p>
See <link href="#multithreading">Multithreading FOP</link> for issues related to changing configuration in a multithreaded environment.
</p>
</section>
<section id="hints">
<title>Hints</title>
<section id="object-reuse">
<title>Object reuse</title>
<p>
If FOP is going to be used multiple times within your application
it may be useful to reuse certain objects to save time.
</p>
<p>
The renderers and the driver can both be reused. A renderer is reusable
once the previous render has been completed. The driver is reuseable
after the rendering is complete and the <code>reset()</code> method is called.
You will need to setup the driver again with a new OutputStream,
IntputStream and renderer.
</p>
</section>
<section id="awt">
<title>AWT issues</title>
<p>
If your XSL-FO files contain SVG then Batik will be used. When Batik is
initialised it uses certain classes in <code>java.awt</code> that
intialises 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 upcoming 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>Driver.getResults()</code>. This returns a FormattingResults object
where you can lookup the number of pages produced. It also gives you the
page-sequences that were produced along with their id attribute and their
number 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 an FileOutputStream, but not
for a ByteArrayOutputStream, for example) it may improve performance considerably
if you buffer the OutputStream using a BufferedOutputStream:
<code>driver.setOutputStream(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 setup a JAXP <code>Templates</code> object and reuse it each time you do
the XSL transformation.
</li>
<li>
Use an XSLT compiler like XSLTC that comes with Xalan-J.
</li>
</ul>
</section>
<section id="multithreading">
<title>Multithreading FOP</title>
<p>
FOP is not currently completely thread safe.
Although the relevant methods of the Driver object are synchronized, FOP uses static
variables for configuration data and loading images.
Here are some tips to mitigate these problems:
</p>
<ul>
<li>
To avoid having your threads blocked, create a Driver object for each thread.
</li>
<li>
If possible, do not change the configuration data while there is a Driver object rendering.
Setup the configuration only once, preferably in the <code>init()</code> method of the servlet.
</li>
<li>
If you must change the configuration data more often, or if you have multiple
servlets within the same webapp using FOP, consider implementing a singleton
class to encapsulate the configuration settings and to run FOP in synchronized methods.
</li>
</ul>
<p>There is also a known issue with fonts being jumbled between threads when using the 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-fir}/examples/embedding" contains several working examples.
In contrast of the examples above the examples here primarily use JAXP for
XML access. This may be easier to understand for people familiar with JAXP.
</p>
<section id="ExampleFO2PDF">
<title>ExampleFO2PDF.java</title>
<p>
This example 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 example 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. <fork href="http://xml.apache.org/xalan-j">Xalan</fork>).
</p>
<figure src="images/EmbeddingExampleXML2FO.png" alt="Example XML to XSL-FO"/>
</section>
<section id="ExampleXML2PDF">
<title>ExampleXML2PDF.java</title>
<p>
This example 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 example 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 a
project team with several members which exist as Java objects to XML.
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.
<fork href="http://java.sun.com/xml/jaxp/dist/1.1/docs/tutorial/xslt/3_generate.html">An older JAXP tutorial</fork>).
</p>
</section>
<section id="ExampleObj2PDF">
<title>ExampleObj2PDF.java</title>
<p>
The last example here 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="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. For examples, you can use a DOMSource
instead of a StreamSource to feed a DOM tree as input for an XSL
transformation.
</p>
<p>
If you think you have a decent example that should be here, contact us via
one of the mailing lists and we'll see to it that it gets added. Also, if
you can't find the solution to your particular problem drop us a message on
the fop-user mailing list.
</p>
</section>
</section>
</body>
</document>
|
