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22.7. Processing XML Stylesheet Transformations

22.7.1. Problem

You have an XML stylesheet that you
want to use to convert XML into something else. For example, you want
to produce HTML from files of XML using the stylesheet.

22.7.2. Solution

Use XML::LibXSLT:

use XML::LibXSLT;
my $xslt       = XML::LibXSLT->new;
my $stylesheet = $xslt->parse_stylesheet_file($XSL_FILENAME);
my $results    = $stylesheet->transform_file($XML_FILENAME);
print $stylesheet->output_string($results);

22.7.3. Discussion

XML::LibXSLT is built on the fast and powerful
libxslt library from the GNOME project. To
perform a transformation, first build a stylesheet object from the
XSL source and then use it to transform an XML file. If you wanted to
(for example, your XSL is dynamically generated rather than being
stored in a file), you could break this down into separate steps:

use XML::LibXSLT;
use XML::LibXML;
my $xml_parser  = XML::LibXML->new;
my $xslt_parser = XML::LibXSLT->new;
my $xml         = $xml_parser->parse_file($XML_FILENAME);
my $xsl         = $xml_parser->parse_file($XSL_FILENAME);
my $stylesheet  = $xslt_parser->parse_stylesheet($xsl);
my $results     = $stylesheet->transform($xml);
my $output      = $stylesheet->output_string($results);

To save the output to a file, use
output_file:

$stylesheet->output_file($OUTPUT_FILENAME);

Similarly, write the output to an already-opened filehandle with
output_fh:

$stylesheet->output_fh($FILEHANDLE);

It''s possible to pass parameters to the transformation engine. For
example, your transformation might use parameters to set a footer at
the bottom of each page:

$stylesheet->transform($xml, footer => "''I Made This!''");

The strange quoting is because the XSLT engine expects to see quoted
values. In the preceding example, the double quotes tell Perl it''s a
string, whereas the single quotes are for the XSLT engine.

You can even retrieve data unavailable to XSLT (from a database,
etc.) or manipulate runtime XSLT data with Perl. Consider the file in
Example 22-10, which has multilingual title tags.

Example 22-10. test.xml

   <list>
<title>System</title>
<TituloGrande>Products</TituloGrande>
<sublist>
<SubTitleOne>Book</SubTitleOne>
</sublist>
</list>

You''d like to call a Perl function match_names
from the XSLT template, test.xsl, given in Example 22-11.

Example 22-11. test.xsl

   <?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"
xmlns:test="urn:test">
<xsl:template match="/">
<xsl:variable name="matched" select="test:match_names(''title | 
titulo | titre | titolo'', . )" />
<xsl:for-each select="$matched">
<xsl:copy-of select="." />
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>

The arguments to match_names are a regex and a
node list, and the function is expected to return a node list object.
Use XML::LibXML::NodeList methods to work with the parameters and
create the return value. The match_names
subroutine is given in Example 22-12.

Example 22-12. match_names subroutine

   sub match_names {
my $pattern = shift;
my $nodelist = shift;
my $matches = XML::LibXML::NodeList->new;
foreach my $context ($nodelist->get_nodelist) {
foreach my $node ($context->findnodes(''//*'')) {
if ($node->nodeName =~ /$pattern/ix) {
$matches->push($node);
}
}
}
return $matches;
}

Use XML::LibXSLT''s register_function method to
register your function for use from an XSLT template. Here''s how
you''d process the template from Example 22-10:

use strict;
use XML::LibXML;
use XML::LibXSLT;
my $xml_parser = XML::LibXML->new;
my $xslt_parser = XML::LibXSLT->new;
sub match_names { ... }   # as in example 22-10
$xslt_parser->register_function("urn:test", "match_names", \&match_names);
my $dom = $xml_parser->parse_file(''test.xml'');
my $xslt_dom = $xml_parser->parse_file(''test.xsl'');
my $xslt = $xslt_parser->parse_stylesheet($xslt_dom);
my $result_dom = $xslt->transform($dom);
print $result_dom->toString;

Use closures to let XSLT access to Perl variables, illustrated here
with an Apache request object:

   $xslt->register_function("urn:test", "get_request",
sub { &get_request($apache_req,@_) } );

The
get_request XSLT function (named in the second
argument to register_function calls the Perl
subroutine get_request (named in the code that is
the third argument) with $apache_req preceding any
arguments given to the XSLT function. You might use this to return a
node list containing HTTP form parameters, or to wrap DBI database
queries.

22.7.4. See Also

The documentation for the modules XML::LibXSLT and
XML::LibXML