Hack 50 Build Results with Literal Result and Instruction Elements

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Use literal result elements, literal text, and instruction elements in an XSLT stylesheet.

This is a hack for XSLT beginners. If you are adding or changing markup in a result tree with XSLT, this hack will help you do it. You will learn how to use literal result elements (along with literal text) and XSLT instruction elements to build your output with new or additional markup.

3.21.1 Literal Result Elements and Literal Text

A literal result element in XSLT is an XML element written literally in a template. Literal result elements can include attributes and must produce well-formed output. Literal text appears as plain, literal text in templates, for stylesheets that have text output.

The stylesheet timedate.xsl, shown in Example 3-35, augments time.xml with additional markup using literal result elements.

Example 3-35. timedate.xsl
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">



<xsl:output method="xml" encoding="ISO-8859-1" indent="yes"/>



   



<xsl:template match="/">



 <instant>



  <xsl:apply-templates select="time"/>



  <date>



   <year>2004</year>



   <month>-06</month>



   <day>-30</day>



  </date>



 </instant>



</xsl:template>



   



<xsl:template match="time">



 <xsl:copy>



  <xsl:attribute name="timezone">



   <xsl:value-of select="@timezone"/>



  </xsl:attribute>



   <xsl:copy-of select="hour|minute|second|atomic"/>



 </xsl:copy>



</xsl:template>



   



</xsl:stylesheet>

On line 2, the output is encoded as Latin1 or ISO-8859-1 (http://en.wikipedia.org/wiki/ISO_8859-1). The template starting on line 4 uses the literal result element instant (see lines 5 and 12) to wrap a new document element around the output. Lines 7 through 11 add new markup as well?the date element with children year, month, and day.

Apply timedate.xsl to time.xml with Xalan C++ or another XSLT processor of your choice. I like Xalan C++ (http://xml.apache.org/xalan-c/) because it's fast and, among other things, allows fine-grained control over indentation with the -i option (follow -i with the number of spaces you want to indent at each level of depth in the structure):

xalan -i 2 time.xml timedate.xsl

You will see this output with new markup highlighted in bold (Example 3-36).

Example 3-36. Output of timedate.xsl
<?xml version="1.0" encoding="ISO-8859-1"?>

<instant>

  <time timezone="PST">

    <hour>11</hour>

    <minute>59</minute>

    <second>59</second>

    <atomic signal="true"/>

  </time>

  <date>

    <year>2004</year>

    <month>-06</month>

    <day>-30</day>

  </date>

</instant>

timetext.xsl in Example 3-37 uses literal text in its template, shown in bold:

Example 3-37. timetext.xsl
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xsl:output method="text"/>

   

<xsl:template match="time">Time: <xsl:value-of select="hour"/>:<xsl:value-of select="minute"/

>:<xsl:value-of select="second"/><xsl:text> </xsl:text>

<xsl:value-of select="meridiem"/>

</xsl:template>

   

</xsl:stylesheet>

The literal text Time: and the two colons (:) will appear in the output along with the other computed values. Apply the stylesheet:

xalan time.xml timetext.xsl

Here is the result:

Time: 11:59:59 p.m.

The text element is an example of an XSLT instruction element. In timetext.xsl, the text element inserts a single space in the output. A discussion on instruction elements follows.

3.21.2 Instruction Elements

We'll discuss the XSLT instruction elements shown in Table 3-1 in this section.

Table 3-1. XSLT instruction elements

Instruction element

Description

element

Writes an element node to the result tree

text

Writes a text node to the result tree

attribute

Writes an attribute node to the result tree

attribute-set

Creates a reusable set of sets that may be used with the use-attribute-sets attribute

comment

Writes a comment to the result tree

processing-instruction

Writes a processing instruction to the result tree


The stylesheet instruct.xsl, shown in Example 3-38, uses all these instruction elements.

Example 3-38. instruct.xsl
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">



<xsl:output method="xml" encoding="UTF-8" indent="yes"/>



<xsl:attribute-set name="att">



 <xsl:attribute name="signal">



  <xsl:value-of select="/time/atomic/@signal"/>



 </xsl:attribute>



 <xsl:attribute name="location">Ft. Collins</xsl:attribute>



</xsl:attribute-set>



   



<xsl:template match="time">



<xsl:processing-instruction name="xml-stylesheet"> href="time.xsl" type="text/xsl" 

</xsl:processing-instruction>



   



<xsl:comment> a time instant </xsl:comment>



   



<xsl:element name="{name( )}" namespace="urn:wyeast-net:xslt">



 <xsl:attribute name="timezone">



  <xsl:value-of select="@timezone"/>



 </xsl:attribute>



 <xsl:element name="hour" xmlns="urn:wyeast-net:xslt">



  <xsl:value-of select="hour"/>



 </xsl:element>



 <xsl:element name="minute" xmlns="urn:wyeast-net:xslt">



  <xsl:value-of select="minute"/>



 </xsl:element>



 <xsl:element name="second" xmlns="urn:wyeast-net:xslt">



  <xsl:value-of select="second"/>



 </xsl:element>



 <xsl:element name="meridiem" xmlns="urn:wyeast-net:xslt">



  <xsl:value-of select="meridiem"/>



 </xsl:element>



 <xsl:element name="atomic" xmlns="urn:wyeast-net:xslt" use-attribute-sets="att"/>



</xsl:element>



</xsl:template>



   



</xsl:stylesheet>

Early on, this stylesheet generates an XML stylesheet processing instruction (line 11) and a comment (line 13). The document element for the result tree is generated based on the name of the matched time element ({name( )} in the name attribute is an attribute value template). An attribute, timezone, is created (line 16) with its value derived from time's timezone attribute.

The namespace attribute states that the new time element will be in a default namespace named with a URN (http://www.ietf.org/rfc/rfc2141.txt), urn:wyeast-net:xslt. Child elements will also be in this namespace (see lines 19-31). Each of these child elements derives its content from corresponding elements in the source document time.xml.

The atomic element uses the attribute set att, defined on lines 3-8. attribute-set is a top-level element, meaning that it must be a child of the stylesheet element. This attribute set has two attributes, signal and location, which will be added to atomic in the result tree.

Apply this stylesheet using this line:

xalan -i 1 time.xml instruct.xsl

The result will look like Example 3-39.

Example 3-39. Output of result.xsl
<?xml version="1.0" encoding="UTF-8"?>

<?xml-stylesheet href="time.xsl" type="text/xsl" ?>

   

<!-- a time instant -->

<time xmlns="urn:wyeast-net:xslt" timezone="PST">

 <hour>11</hour>

 <minute>59</minute>

 <second>59</second>

 <meridiem>p.m.</meridiem>

 <atomic signal="true" location="Ft. Collins"/>

</time>



     
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