XSL - Transformer in Java

XSL Implementations in J2SDK

J2SDK 1.4.1_01 offers the following interfaces to support XSL:

• javax.xml.transform.TransformerFactory: The transformer factory class to help to create a transformer object.
• javax.xml.transform.Transformer: The abstract class representing a transformer.
• javax.xml.transform.Source: The interface representing source objects for the transformer to process.
• javax.xml.transform.Result: The interface representing result objects produced by the transformer.

One thing is missing here: who represents the transformation style rules? The answer is that javax.xml.transform.Source also represents transformation style rules, because they written in XML.

I have a simple program here, XSLClassChecker.java, to show what are the XSL implementation classes:

/**
 * XSLClassChecker.java
 * Copyright (c) 2002 by Dr. Herong Yang
 */
import javax.xml.transform.Source;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.stream.StreamSource;
import javax.xml.transform.stream.StreamResult;
class XSLClassChecker {
   public static void main(String[] args) {
      try {
         TransformerFactory f = TransformerFactory.newInstance();
         System.out.println(f.toString());
         Transformer t = f.newTransformer();
         System.out.println(t.toString());
         Source s = new StreamSource();
         System.out.println(s.toString());
         Result r = new StreamResult();
         System.out.println(r.toString());
         t.transform(s,r);
      } catch (TransformerConfigurationException e) {
         System.out.println(e.toString()); 	
      } catch (TransformerException e) {
         System.out.println(e.toString()); 	
      }
   }
}

Output:

org.apache.xalan.processor.TransformerFactoryImpl@119298d
org.apache.xalan.transformer.TransformerIdentityImpl@1f33675
javax.xml.transform.stream.StreamSource@1690726
javax.xml.transform.stream.StreamResult@9931f5
javax.xml.transform.TransformerException: No output specified

Note that:

• So J2SDK 1.4.1_01 is using the org.apache.xalan package for XSL transformation.
• The Identity transformer was used, because the program is specify any transformation rules.
• I got the "No output specified" exception, because the program was transforming from nothing (empty source object) to nowhere (empty result object).

A Simple XSL Transformer Program

Here is my first XSL transformation program in Java:

/**
 * XSLTransformer.java
 * Copyright (c) 2002 by Dr. Herong Yang
 */
import java.io.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;
class XSLTransformer {
   public static void main(String[] args) {
      try {
      	 File sf = new File(args[0]); // source file
      	 File rf = new File(args[1]); // result file
      	 File tf = new File(args[2]); // template file
         TransformerFactory f = TransformerFactory.newInstance();
         Transformer t = f.newTransformer(new StreamSource(tf));
         Source s = new StreamSource(sf);
         Result r = new StreamResult(rf);
         t.transform(s,r);
      } catch (TransformerConfigurationException e) {
         System.out.println(e.toString()); 	
      } catch (TransformerException e) {
         System.out.println(e.toString());
      }
   }
}

Let's try this program with my hello.xml as the source file:

<?xml version="1.0"?>
<p>Hello world!</p>

and my hello.xsl as the template file that contains the transformation style rules:

<?xml version="1.0"?>
<xsl:stylesheet version="1.0"
   xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 <xsl:template match="p">Hello world.! - From hello.xsl.</xsl:template>
</xsl:stylesheet>

Run "java XSLTransformer hello.xml hello.out hello.xsl", I got in hello.out:

<?xml version="1.0" encoding="UTF-8"?>
Hello world! - From hello.xsl.

Source: Herong's Notes on XML.