XSLT, or Extensible Style Language for Transformations, allows you a great deal of control over the output format. It can be used to change an XML file from one DTD into another, as might be needed in a business-to-business (B2B) application where information is passed from one industry-standard DTD to a site that uses another. It can also be used to render XML into another format such as HTML. Think of XSLT as a scripting language for transforming XML.
You need a set of classes called an XSLT
processor
. One
freely available XSLT processor is the
Apache project’s Xalan
(formerly available from Lotus/IBM as the Lotus XSL processor). To
use this, you create an XSL processor by calling the factory method
getProcessor( )
,
then call its parse method passing in two
XSLTInputSources
(one for the XML document and one for the XSL stylesheet) and one
XSLTResultTarget
for the output file.
Assume you have a file of people’s
names,
addresses, and so on, stored in an XML document such as the file
people.xml, shown in Example 21-1.
Example 21-1. people.xml
<?xml version="1.0"?>
<people>
<person>
<name>Ian Darwin</name>
<email>[email protected]</email>
<country>Canada</country>
</person>
<person>
<name>Another Darwin</name>
<email type="intranet">ad</email>
<country>Canada</country>
</person>
</people>You can transform the
people.xml
file into HTML by using
the following command:
$ java XSLTransform people.xml people.xsl people.html
Figure 21-2 shows the resulting HTML file opened in a browser.
Let’s look at the file people.xsl (shown
in Example 21-2). Since an XSL file is an XML file, it must be
well-formed
according to the syntax of XML. As you can see, it contains some XML
elements but is mostly (well-formed) HTML.
Example 21-2. people.xsl
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:template match="/">
<html>
<head><title>Our People</title></head>
<body>
<table border="1">
<tr>
<th>Name</th>
<th>EMail</th>
</tr>
<xsl:for-each select="people/person">
<tr>
<td><xsl:value-of select="name"/></td>
<td><xsl:value-of select="email"/></td>
</tr>
</xsl:for-each>
</table>
</body></html>
</xsl:template>
</xsl:stylesheet>The program XSLTransform appears in Example 21-3.
Example 21-3. XSLTransform.java
import org.apache.xalan.xslt.*;
import java.net.*;
import java.io.*;
/**
* Demonstrate transforming a file using XSLT.
*/
public class XSLTransform {
public static void main(String[] args) {
try {
// Require three input args
if (args.length != 3) {
System.out.println("Usage: java XSLTransform "
+ "<input XML file> <input XSL file> <output file>");
System.exit(1);
}
XSLTProcessor myProcessor = XSLTProcessorFactory.getProcessor( );
XSLTInputSource xmlSource = new XSLTInputSource(args[0]);
XSLTInputSource xslStylesheet = new XSLTInputSource(args[1]);
XSLTResultTarget xmlOutput = new XSLTResultTarget(args[2]);
myProcessor.process(xmlSource, xslStylesheet, xmlOutput);
}
catch (org.xml.sax.SAXException exc) {
System.err.println("Found invalid XML during processing:");
exc.printStackTrace( );
}
}
}A new development in progress is the use of
translets. Sun is developing a program that will
read a stylesheet and generate a
Translet
class,
which is a compiled Java program that transforms XML according to the
stylesheet. This will eliminate the overhead of reading the
stylesheet each time a document is translated. See http://www.sun.com/xml/developers/xsltc/.