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Transformations API for XML

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by , 11-07-2011 at 07:36 PM (4370 Views)
In the next few posts, I will write about how to perform an XSLT transformation using StAX APIs: Cursor API and Event Iterator API.

TrAX (Transformations API for XML) is a Java API for performing XSLT transformations. In J2SE 1.5, there are three different ways to represent the source and the result of an XSLT transformation and they are: by XML stream source/result, by SAX events source/result, and by DOM tree source/result. In J2SE 1.6 an XSLT transformation is performed using a StAX (Streaming API for XML) source as an input and a StAX result as an output.

To get started, you should have Java 1.6 installed and working on your machine. Also you should have some knowledge of XSLT and StAX.

Lets start with XSLT/TrAX transformation process.

Firstly, we have to obtain a javax.xml.transform.TransformerFactory object. This class provides an XSLT processor. To obtain its object, we will instantiate this class by calling the newInstance method.

Java Code:
TransformerFactory transfFactory=TransformerFactory.newInstance();
We also have to set the javax.xml.transform.TransformerFactory system property:

Java Code:
//setting the javax.xml.transform.TransformerFactory system property for the Saxon processor
//setting the javax.xml.transform.TransformerFactory system property for the Xalan processor

Second step is to provide a javax.xml.transform.Source object for the XSL stylesheet. For this, you have to instantiate the proper XXXSource class.

Now is the time to obtain a javax.xml.transform.Transformer object. This is done by calling the newTransformer method. This object will transform the source-tree into result-tree.

Java Code:
public abstract Transformer newTransformer(Source source) throws
The newTransformer method expects the source of the XSL stylesheet as parameter.

We also have to indicate the XML document for transformation. This is done by creating another Source object. For this one has to instantiate the proper XXXSource class.

Now is the time to create a javax.xml.transform.Result object. Also we have to decide what kind of result we will use and then we havet o instantiate the proper XXXResult class.

To start the transformationm Transformer.transform method is called. This method retrieves the Source of the XML document (that we wish to transform) and the Result of that transformation:

Java Code:
public abstract void transform(Source XMLs, Result result)throws
The six steps discussed here makes XSLT transformation based on the StAXSource/StAXResult classes very simple and easy. The actual task is to create the StAXSource/StAXResult objects and the using the required constructor.

Time for an example. Suppose we have following XML file:

<!--?xml version="1.0" encoding="UTF-8" standalone="no" ?-->
<!--?xml-stylesheet type="text/xsl" href="xslFile.xsl"?-->

<name>Martin Hook</name>
Also we have the following XSL style sheet:

<!--?xml version="1.0" encoding="UTF-8"?-->

<xsl:stylesheet version="1.0" xmlns:xsl="">

<xsl:output method="html" version="4.01" encoding="ISO-8859-1">indent="yes" media-type="text/html" /&gt;
<xsl:template match="/member">


<font face="arial" size="3"><strong><em>Name:</em></strong></font>
<font face="arial" size="5"><xsl:value-of select="//name"></xsl:value-of></font>

<font face="arial" size="3"><strong><em>E-mail:</em></strong></font>
<font face="arial" size="5"><xsl:value-of select="//e-mail"></xsl:value-of></font>



To create StAXSource for the XSL, we use Cursor API as shown in the snippet below:
Java Code:
XMLStreamReader streamReaderXSL=null;

//define the Source object for the stylesheet
Source XSL=new StAXSource(streamReaderXSL);

Continuing with the example, we have following code for the XML document:

Java Code:
XMLStreamReader streamReaderXML=null;

//define the Source object for the XML document
Source XML=new StAXSource(streamReaderXML);
Transformation results in the following:
Java Code:
XMLStreamWriter streamWriter=null;

//define the Result object
Result XML_r=new StAXResult(streamWriter);
If you want to use Event Iterator API, the code snippet presented below will be useful for you.

Java Code:
XMLEventReader eventReaderXSL=null;
//define the Source object for the stylesheet
XSL=new StAXSource(eventReaderXSL);

// for XML file

XMLEventReader eventReaderXML=null;
//define the Source object for the XML document
XML=new StAXSource(eventReaderXML);

// result fo transformation

XMLStreamWriter streamWriter=null;
//define the Result object
Result XML_r=new StAXResult(streamWriter);
Hope this helps.

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Java SE , XML