Passing Parameters to Style Sheets

Top-level xsl:param and xsl:variable elements both define variables by binding a name to a value. This variable can be dereferenced elsewhere in the stylesheet using the form $name. Once set, the value of an XSLT variable is fixed and cannot be changed. However if the variable is defined with a top-level xsl:param element instead of an xsl:variable element, then the default value can be changed before the transformation begins.

For example, the DocBook XSL stylesheets have a number of parameters that set various formatting options. I use these settings:

  <xsl:param name="fop.extensions">1</xsl:param>
  <xsl:param name="page.width.portrait">7.375in</xsl:param>
  <xsl:param name="page.height.portrait">9.25in</xsl:param>

  <xsl:param name="page.margin.top">0.5in</xsl:param>
  <xsl:param name="page.margin.bottom">0.5in</xsl:param>
  <xsl:param name="region.before.extent">0.5in</xsl:param>
  <xsl:param name="body.margin.top">0.5in</xsl:param>

  <xsl:param name="page.margin.outer">1.0in</xsl:param>
  <xsl:param name="page.margin.inner">1.0in</xsl:param>
  <xsl:param name="body.font.family">Times</xsl:param>
  <xsl:param name="variablelist.as.blocks" select="1"/>

  <xsl:param name="generate.section.toc.level" select="1"/>
  <xsl:param name="generate.component.toc" select="0"/>

The initial (and thus final) value of any parameter can be changed inside your Java code using these three methods of the Transformer class:

The setParameter() method provides a value for a parameter that overrides any value used in the stylesheet itself. The processor is responsible for converting the Java object type passed to a reasonable XSLT equivalent. This should work well enough for String, Integer, Double, and Boolean as well as DOM types like Node and NodeList. However, I wouldn’t rely on it for anything more complex like a File or a Frame.

The getParameter() method returns the value of a parameter previously set by Java. It will not return any value from the stylesheet itself, even if it has not been overridden by the Java code. Finally, the clearParameters() method eliminates all Java mappings of parameters so that those variables are returned to whatever value is specified in the stylesheet.

For example, in Java the above list of parameters for the DocBook stylesheets could be set with a JAXP Transformer object like this:

transformer.setParameter("fop.extensions", "1");
transformer.setParameter("page.width.portrait", "7.375in");
transformer.setParameter("page.height.portrait", "9.25in");
transformer.setParameter("page.margin.top", "0.5in");
transformer.setParameter("region.before.extent", "0.5in");
transformer.setParameter("body.margin.top", "0.5in");
transformer.setParameter("page.margin.bottom", "0.5in");
transformer.setParameter("page.margin.outer", "1.0in");
transformer.setParameter("page.margin.inner", "1.0in");
transformer.setParameter("body.font.family", "Times");
transformer.setParameter("variablelist.as.blocks", "1");
transformer.setParameter("generate.section.toc.level", "1");
transformer.setParameter("generate.component.toc", "0");

Here I used strings for all the values. However, in a few cases I could have used a Number of some kind instead.