Dynamically include other XSL files in XSLT

Question

I have a small problem, is there a way to dynamically include another xsl? For example:

<xsl:variable name="PathToWeb" select="'wewe'"/>
<xsl:include href="http://{$PathToWeb}/html/xsl/head.xsl" />
<xsl:include href="http://{$PathToWeb}/html/xsl/navigation.xsl" />
<xsl:include href="http://{$PathToWeb}/html/xsl/promo.xsl" />
<xsl:include href="http://{$PathToWeb}/html/xsl/3columns.xsl" />

<xsl:include href="http://{$PathToWeb}/html/xsl/footer.xsl" />

Answer 1

I have solved this problem differently, might be useful for someone who works with Java and XSLT (this solution is specific to people using javax.xml.transform package).

XSLT transformer factory allows setting a custom URI resolver. Say if your XSLT looks like

<?xml version="1.0" encoding="utf-8"?>
  <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="html" version="4.0" encoding="UTF-8"/>
    <xsl:include href="import://stackoverflow.com/xsl"/>
    ...

The URI resolver's resolve method will get import://stackoverflow.com/xsl as a href parameter. import:// could serve as a "special" identifier scheme for custom includes, so you can detect it and create/return javax.xml.transform.Source which is pointing to the necessary file. For example:

TransformerFactory tf = TransformerFactory.newInstance();
URIResolver delegate = tf.getURIResolver();
tf.setURIResolver( new CustomURIResolver( delegate ) );

Then, inside CustomURIResolver:

  public Source resolve( String href, String base )
    throws TransformerException {
    Source result = null;
    URI uri = null;

    try {
      uri = new URI( href );
    }
    catch( Exception e ) {
      throw new TransformerException( e );
    }

    // The XSLT file has a URI path that allows for a file to be included
    // dynamically.
    if( "import".equalsIgnoreCase( uri.getScheme() ) &&
        "stackoverflow.com".equalsIgnoreCase( uri.getAuthority() ) ) {
      result = openTemplate();
    }
    else {
      result = getDelegate().resolve( href, base );
    }

    return result;
  }

Add an openTemplate() method that includes the logic to dynamically determine the XSL file to open.

Answer 2

I have a small problem, is there a way to dynamically include another xsl? For example:

<xsl:variable name="PathToWeb" select="'wewe'"/> 
<xsl:include href="http://{$PathToWeb}/html/xsl/head.xsl" /> 
<xsl:include href="http://{$PathToWeb}/html/xsl/navigation.xsl" /> 
<xsl:include href="http://{$PathToWeb}/html/xsl/promo.xsl" /> 
<xsl:include href="http://{$PathToWeb}/html/xsl/3columns.xsl" /> 

<xsl:include href="http://{$PathToWeb}/html/xsl/footer.xsl" />

It is illegal to have a variable reference in the href attribute of <xsl:include>. According to the W3C XSLT 1.0 and XSLT 2.0 specifications, the value of this attribute must be an URI reference.

However, if the value of the $PathToWeb variable is known before the start of the transformation, it can be used in a number of ways to produce dynamically a stylesheet representation in which the <xsl:include> statements above contain the desires URIs (after substituting the reference to $PathToWeb with the required value:

1. Generate a new stylesheet from the current one, using XSLT.

2. Load the stylesheet as an XmlDocument object. Then locate the respective <xsl:include> elements and set their href attributes to the desired values. Finally, invoke the transformation using the so modified XmlDocument that represents the stylesheet.

Method 2. has been used for 11 years in the XPath Visualizer to dynamically set the exact value of a select attribute used to select all nodes that a user-entered XPath expression selects and to generate an HTML document representing the XML document with all selected and visible nodes highlighted.

Answer 3

You cannot do this. The reasons are simple :

XSL will first expand the xsl:include during compilation, before it does anything else. At that point your "variable" is not know and cannot be known and you can't change the compiled transform once it compiles. In addition the href is a Uniform Resource Locator not an XPath expression, therefore you can't just expand a variable in it.