Chapter 4 XML Processing

177

chain of filters and each filter implements a processing step. XML processing 

techniques such as SAX work well with this design. 

The two designs can, of course, be combined. When combined, transforma 

tions and identity transformations become handy techniques to use when the result

of a processing step cannot be directly wrapped into a 

Source

 object compatible

with the next step. JAXP also provides support for chaining transformations with

the use of 

javax.xml.transform.sax.SAXTransformerFactory

.

Code Example 4.10 illustrates an XML processing pipeline that combines

SAX and XSLT to validate an incoming purchase order document, extract on the 

fly the purchase order identifier, and transform the incoming document from its

external, XSD based schema to the internal, DTD based schema supported by the

business logic. The code uses a SAX filter chain as the 

Source

 of a transforma 

tion. Alternatively, the code could have used a 

SAXTransformerFactory

 to create

an 

org.xml.sax.XMLFilter

 to handle the transformation and then chain it to the

custom 

XMLFilter

, which extracts the purchase order identifier.

public class SupplierOrderXDE extends 

XMLDocumentEditor.DefaultXDE {

public static final String DEFAULT_ENCODING = "UTF 8";

private XMLFilter filter;

private Transformer transformer;

private Source source = null;

private String orderId = null;

public SupplierOrderXDE(boolean validating, ...) {

// Create a [validating] SAX parser 

SAXParser parser = ...;

filter = new XMLFilterImpl(parser.getXMLReader()) {

// Implements a SAX XMLFilter that extracts the OrderID

// element value and assigns it to the orderId attribute

};

// Retrieve the style sheet as a stream

InputStream stream = ...;

// Create a transformer from the stylesheet

transformer = TransformerFactory.newInstance()

.newTransformer(new StreamSource(stream));

}

// Sets the document to be processed