172

Implementing XML Based Applications

implementation is layered on top of SAX 2.0 and does not maintain an addi 

tional underlying representation of the source document. Additionally, where 

DOM represents all XML schema numeric types as strings, JAXB's standard 

implementation maps these values directly to much more compact Java numer 

ic data types. Not only does this use less memory to represent the same content, 

the JAXB approach saves time, because converting between the two represen 

tations is not necessary.

E

You previously were implementing XML data binding manually with DOM, 

and an XSD schema definition is available.

4.4.1.4

XSLT Programming Model

XSLT is a higher level processing model than the SAX, DOM, and XML data 

binding models. Although developers can mimic XSLT by implementing transfor 

mations programmatically on top of SAX, DOM, or the XML data binding model,

XSLT does not compare with other processing models and should be regarded as

complementary, to be used along with these other models.

XSLT implements a functional declarative model as opposed to a procedural

model. This requires skills that are quite different from Java programming skills.

For the most part, XSLT requires developers to code rules, or templates, that are

applied when specified patterns are encountered in the source document. The

application of the rules adds new fragments or copies fragments from the source

tree to a result tree. The patterns are expressed in the Xpath language, which is

used to locate and extract information from the source document. 

Instead of writing Java code (as with SAX, DOM, and the XML data binding

model), developers using XSLT principally write style sheets, which are them 

selves XML documents. (Invoking the XSLT engine, however, does require the

developer to write Java code.) Compared to the other programming models, XSLT

programming gives developers the sort of flexibility that comes with scripting. In

an XML based application, XSLT processing is usually used along with the other

three processing models. The XSLT API available with JAXP provides an

abstraction for the source and result of transformations, allowing the developer

not only the ability to chain transformations but also to interface with other pro 

cessing models, such as SAX, DOM, and JAXB technology. To interface with

SAX and DOM, use the classes 

SAXSource

, 

SAXResult

, 

DOMSource

, and 

DOMResult

provided by JAXP. To interface with JAXB, use the classes 

JAXBSource

 and

JAXBResult

.