Example: Creating a simple PDF plug-in

This scenario walks through the process of creating a very simple plug-in (com.example.print-pdf) that creates a new transformation type: print-pdf.

The print-pdf transformation has the following characteristics:

• Uses A4 paper
• Renders figures with a title at the top and a description at the bottom
• Removes the period after the number for an ordered-list item
• Use em dashes as the symbols for unordered lists

1. In the plugins directory, create a directory named com.example.print-pdf.

2. In the new com.example.print-pdf directory, create a plug-in configuration file (plugin.xml) that declares the new print-pdf transformation and its dependencies.

   <?xml version="1.0" encoding="UTF-8"?>
   <?xml-model href="https://www.dita-ot.org/rng/plugin.rnc" type="application/relax-ng-compact-syntax"?>
   
   <plugin id="com.example.print-pdf">
     <require plugin="org.dita.pdf2"/>
     <transtype name="print-pdf" extends="pdf" desc="PDF on A4 paper"/>
     <feature extension="dita.transtype.print" value="print-pdf"/>
     <feature extension="ant.import" file="integrator.xml"/>
   </plugin>
   

3. Add an Ant script (integrator.xml) to define the transformation type.

   <?xml version='1.0' encoding='UTF-8'?>
   <project>
     <target name="dita2print-pdf"
          depends="dita2print-pdf.init,
                   dita2pdf2"/>
     <target name="dita2print-pdf.init">
       <property name="customization.dir"
             location="${dita.plugin.com.example.print-pdf.dir}/cfg"/>
      </target>
   </project>
   

4. In the new plug-in directory, add a cfg/catalog.xml file that specifies the custom XSLT style sheets.

   <?xml version="1.0" encoding="UTF-8"?>
   <catalog prefer="system"
            xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
     <uri name="cfg:fo/attrs/custom.xsl" uri="fo/attrs/custom.xsl"/>
     <uri name="cfg:fo/xsl/custom.xsl" uri="fo/xsl/custom.xsl"/>
   </catalog>
   

5. Create the cfg/fo/attrs/custom.xsl file, and add attribute and variable overrides to it.

   For example, add the following variables to change the page size to A4.

   <?xml version="1.0" encoding="UTF-8"?>
   <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                   version="2.0">
     <!-- Change page size to A4 -->
     <xsl:variable name="page-width">210mm</xsl:variable>
     <xsl:variable name="page-height">297mm</xsl:variable>
   </xsl:stylesheet>
   

6. Create the cfg/fo/xsl/custom.xsl file, and add XSLT overrides to it.

   For example, the following code changes the rendering of <figure> elements.

   <?xml version="1.0" encoding="UTF-8"?>
   <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                   xmlns:xs="http://www.w3.org/2001/XMLSchema"
                   xmlns:fo="http://www.w3.org/1999/XSL/Format"
                   version="2.0">
     <!-- Move figure title to top and description to bottom -->
     <xsl:template match="*[contains(@class,' topic/fig ')]">
       <fo:block xsl:use-attribute-sets="fig">
         <xsl:call-template name="commonattributes"/>
         <xsl:if test="not(@id)">
           <xsl:attribute name="id">
             <xsl:call-template name="get-id"/>
           </xsl:attribute>
         </xsl:if>
         <xsl:apply-templates select="*[contains(@class,' topic/title ')]"/>
         <xsl:apply-templates select="*[not(contains(@class,' topic/title ') or contains(@class,' topic/desc '))]"/>
         <xsl:apply-templates select="*[contains(@class,' topic/desc ')]"/>
       </fo:block>
     </xsl:template>
   </xsl:stylesheet>
   

7. Create an English-language variable-definition file (cfg/common/vars/en.xml) and make any necessary modifications to it.

   For example, the following code removes the period after the number for an ordered-list item; it also specifies that the bullet for an unordered list item should be an em dash.

   <?xml version="1.0" encoding="UTF-8"?>
   <variables>
     <!-- Remove dot from list number -->
     <variable id="Ordered List Number 1">
       <param ref-name="number"/>
     </variable>
     <!-- Change unordered list bullet to an em dash -->
     <variable id="Unordered List bullet 1">&#x2014;</variable>
   </variables>
   

Tip: The files for this sample plug-in are included in the DITA-OT installation directory under docsrc/samples/plugins/com.example.print-pdf/ and on GitHub.

The plug-in directory has the following layout and files:

com.example.print-pdf
├── cfg
│   ├── catalog.xml
│   ├── common
│   │   └── vars
│   │       └── en.xml
│   └── fo
│       ├── attrs
│       │   └── custom.xsl
│       └── xsl
│           └── custom.xsl
├── integrator.xml
└── plugin.xml

1. Use the dita install subcommand to install the plug-in.

   Note: For more information, see Installing plug-ins.

2. Build output with the new transformation type to verify that the plug-in works as intended.

   ``dita`` **--input**=*my.ditamap* **--format**=print-pdf
   

Related information

Installing plug-ins