xdocs/sources/xsltc/xsl_include_design.xml - xalan-j - Git at Google

 <?xml version="1.0" standalone="no"?>
 <!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
 <!--
  * The Apache Software License, Version 1.1
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  *
  * Copyright (c) 2001 The Apache Software Foundation.  All rights
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  *    notice, this list of conditions and the following disclaimer.
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  * 2. Redistributions in binary form must reproduce the above copyright
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  * 3. The end-user documentation included with the redistribution,
  *    if any, must include the following acknowledgment:
  *       "This product includes software developed by the
  *        Apache Software Foundation (http://www.apache.org/)."
  *    Alternately, this acknowledgment may appear in the software itself,
  *    if and wherever such third-party acknowledgments normally appear.
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  * 4. The names "Xalan" and "Apache Software Foundation" must
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  * 5. Products derived from this software may not be called "Apache",
  *    nor may "Apache" appear in their name, without prior written
  *    permission of the Apache Software Foundation.
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  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
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  * This software consists of voluntary contributions made by many
  * individuals on behalf of the Apache Software Foundation and was
  * originally based on software copyright (c) 2001, Sun
  * Microsystems., http://www.sun.com.  For more
  * information on the Apache Software Foundation, please see
  * <http://www.apache.org/>.
  -->
   <s1 title="&lt;xsl:include&gt; / &lt;xsl:import&gt;">

   <s2 title="Contents">
   <ul>
     <li><link anchor="functionality">Functionality</link></li>
     <li><link anchor="implementation">Implementation</link></li>
   </ul>
   </s2>

   <anchor name="functionality"/>
   <s2 title="Functionality">

     <p><code>&lt;xsl:include&gt;</code> allows you to include one stylesheet
     into another. The includ<em>ed</em> stylesheet's templates will have the same
     default priorities and import precedence as the includ<em>ing</em> stylesheet.
     <code>&lt;xsl:import&gt;</code> offers the same, but the import precedence
     of elements in an import<em>ed</em> stylesheet is always less than that of
     the import<em>ing</em> stylesheet.</p>

   </s2>

   <anchor name="implementation"/>
   <s2 title="Implementation">

     <anchor name="include"/>
     <s3 title="&lt;xsl:include&gt;">

     <p>This is the simplest case, so we will look at that first. The algorithm
     for including another stylesheet is roughly:</p>

     <ul>
       <li>get the including stylesheet from the XSLT parser</li>
       <li>get the value of the "href" attribute from the
         <code>&lt;xsl:include&gt;</code> element and check for circular
         includes/imports</li>
       <li>check if there is a defined <code>SourceLoader</code> set either
         through the native or the TrAX API</li>
       <li>get an <code>InputSource</code> for the document to include, either
         from the <code>SourceLoader</code> or from the document's URI</li>
       <li>parse the input document using the compiler's XSLT parser</li>
       <li>set the import precedence of the included stylesheet to the same as
         the import precedence of the including stylesheet</li>
       <li>get the top-level stylesheet from the XSLT parser</li>
       <li>move all variables, parameters, and top-level elements (include
         templates) from the included stylesheet to the top-level stylesheet
         (all elements will keep their import precedence even after being moved
         to the top-level stylesheet)</li>
     </ul>

     </s3>

     <anchor name="import"/>
     <s3 title="&lt;xsl:import&gt;">

     <p>This is very similar to <code>&lt;xsl:include&gt;</code>, but import
     precedence has to be handled differently. Looking at the code you'll find
     this fragment:</p><source>
     // Handle precedence for the including stylesheet
     final int currPrecedence = parser.getCurrentImportPrecedence();
     final int nextPrecedence = parser.getNextImportPrecedence();
     _imported.setImportPrecedence(currPrecedence);
     context.setImportPrecedence(nextPrecedence);</source>

     <p>The important thing here is that the imported stylesheet has import
     precedence <em>less</em> than the importing stylesheet. So the imported
     stylesheet gets the current import precedence, while the current stylesheet
     gets the next available (unused) import precedence. The
     <code>Stylesheet</code> class has a method
     <code>setImportPrecedence()</code> that ensures that the import precedence
     is set not only for the stylesheet itself, but that it is also propagated
     down to any included/imported stylesheets:</p><source>
     public void setImportPrecedence(final int precedence) {
 	// Set import precedence for this stylesheet
 	_importPrecedence = precedence;

 	// Set import precedence for all included stylesheets
 	final Enumeration elements = elements();
 	while (elements.hasMoreElements()) {
 	    SyntaxTreeNode child = (SyntaxTreeNode)elements.nextElement();
 	    if (child instanceof Include) {
 		Stylesheet included = ((Include)child).getIncludedStylesheet();
 		if (included != null) included.setImportPrecedence(precedence);
 	    }
 	}

 	// Set import precedence for the stylesheet that imported this one
 	if (_importedFrom != null) {
 	    if (_importedFrom.getImportPrecedence() &lt; precedence) {
 		final Parser parser = getParser();
 		final int nextPrecedence = parser.getNextImportPrecedence();
 		_importedFrom.setImportPrecedence(nextPrecedence);
 	    }
 	}
 	// Set import precedence for the stylesheet that included this one
 	else if (_includedFrom != null) {
 	    if (_includedFrom.getImportPrecedence() != precedence)
 		_includedFrom.setImportPrecedence(precedence);
 	}
     }</source>

     <p>This method has been carefully cluttered together, and it works, and it
     should not be touched.</p>

     </s3>

     <anchor name="apply-imports"/>
     <s3 title="&lt;xsl:apply-imports&gt;">

     </s3>

   </s2>

 </s1>
	<?xml version="1.0" standalone="no"?>
	<!DOCTYPE s1 SYSTEM "../../style/dtd/document.dtd">
	<!--
	* The Apache Software License, Version 1.1
	*
	*
	* Copyright (c) 2001 The Apache Software Foundation. All rights
	* reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	*
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	*
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in
	* the documentation and/or other materials provided with the
	* distribution.
	*
	* 3. The end-user documentation included with the redistribution,
	* if any, must include the following acknowledgment:
	* "This product includes software developed by the
	* Apache Software Foundation (http://www.apache.org/)."
	* Alternately, this acknowledgment may appear in the software itself,
	* if and wherever such third-party acknowledgments normally appear.
	*
	* 4. The names "Xalan" and "Apache Software Foundation" must
	* not be used to endorse or promote products derived from this
	* software without prior written permission. For written
	* permission, please contact apache@apache.org.
	*
	* 5. Products derived from this software may not be called "Apache",
	* nor may "Apache" appear in their name, without prior written
	* permission of the Apache Software Foundation.
	*
	* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
	* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
	* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
	* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
	* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
	* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	* SUCH DAMAGE.
	* ====================================================================
	*
	* This software consists of voluntary contributions made by many
	* individuals on behalf of the Apache Software Foundation and was
	* originally based on software copyright (c) 2001, Sun
	* Microsystems., http://www.sun.com. For more
	* information on the Apache Software Foundation, please see
	* <http://www.apache.org/>.
	-->
	<s1 title="<xsl:include> / <xsl:import>">

	<s2 title="Contents">
	<ul>
	<li><link anchor="functionality">Functionality</link></li>
	<li><link anchor="implementation">Implementation</link></li>
	</ul>
	</s2>

	<anchor name="functionality"/>
	<s2 title="Functionality">

	<p><code><xsl:include></code> allows you to include one stylesheet
	into another. The includ<em>ed</em> stylesheet's templates will have the same
	default priorities and import precedence as the includ<em>ing</em> stylesheet.
	<code><xsl:import></code> offers the same, but the import precedence
	of elements in an import<em>ed</em> stylesheet is always less than that of
	the import<em>ing</em> stylesheet.</p>

	</s2>

	<anchor name="implementation"/>
	<s2 title="Implementation">

	<anchor name="include"/>
	<s3 title="<xsl:include>">

	<p>This is the simplest case, so we will look at that first. The algorithm
	for including another stylesheet is roughly:</p>

	<ul>
	<li>get the including stylesheet from the XSLT parser</li>
	<li>get the value of the "href" attribute from the
	<code><xsl:include></code> element and check for circular
	includes/imports</li>
	<li>check if there is a defined <code>SourceLoader</code> set either
	through the native or the TrAX API</li>
	<li>get an <code>InputSource</code> for the document to include, either
	from the <code>SourceLoader</code> or from the document's URI</li>
	<li>parse the input document using the compiler's XSLT parser</li>
	<li>set the import precedence of the included stylesheet to the same as
	the import precedence of the including stylesheet</li>
	<li>get the top-level stylesheet from the XSLT parser</li>
	<li>move all variables, parameters, and top-level elements (include
	templates) from the included stylesheet to the top-level stylesheet
	(all elements will keep their import precedence even after being moved
	to the top-level stylesheet)</li>
	</ul>

	</s3>

	<anchor name="import"/>
	<s3 title="<xsl:import>">

	<p>This is very similar to <code><xsl:include></code>, but import
	precedence has to be handled differently. Looking at the code you'll find
	this fragment:</p><source>
	// Handle precedence for the including stylesheet
	final int currPrecedence = parser.getCurrentImportPrecedence();
	final int nextPrecedence = parser.getNextImportPrecedence();
	_imported.setImportPrecedence(currPrecedence);
	context.setImportPrecedence(nextPrecedence);</source>

	<p>The important thing here is that the imported stylesheet has import
	precedence <em>less</em> than the importing stylesheet. So the imported
	stylesheet gets the current import precedence, while the current stylesheet
	gets the next available (unused) import precedence. The
	<code>Stylesheet</code> class has a method
	<code>setImportPrecedence()</code> that ensures that the import precedence
	is set not only for the stylesheet itself, but that it is also propagated
	down to any included/imported stylesheets:</p><source>
	public void setImportPrecedence(final int precedence) {
	// Set import precedence for this stylesheet
	_importPrecedence = precedence;

	// Set import precedence for all included stylesheets
	final Enumeration elements = elements();
	while (elements.hasMoreElements()) {
	SyntaxTreeNode child = (SyntaxTreeNode)elements.nextElement();
	if (child instanceof Include) {
	Stylesheet included = ((Include)child).getIncludedStylesheet();
	if (included != null) included.setImportPrecedence(precedence);
	}
	}

	// Set import precedence for the stylesheet that imported this one
	if (_importedFrom != null) {
	if (_importedFrom.getImportPrecedence() < precedence) {
	final Parser parser = getParser();
	final int nextPrecedence = parser.getNextImportPrecedence();
	_importedFrom.setImportPrecedence(nextPrecedence);
	}
	}
	// Set import precedence for the stylesheet that included this one
	else if (_includedFrom != null) {
	if (_includedFrom.getImportPrecedence() != precedence)
	_includedFrom.setImportPrecedence(precedence);
	}
	}</source>

	<p>This method has been carefully cluttered together, and it works, and it
	should not be touched.</p>

	</s3>

	<anchor name="apply-imports"/>
	<s3 title="<xsl:apply-imports>">

	</s3>

	</s2>

	</s1>