176

Implementing XML Based Applications

Table 4.1

DOM, SAX, and XML Data Binding Programming Models (

continued

)

DOM

SAX

XML Data Binding

High memory usage (The 

Low memory usage (only 

Intermediate memory usage 

document is often completely 

events are generated)

(The document is often com 

loaded in memory, though 

pletely loaded in memory, but 

some techniques such as 

the Java representation of the 

deferred or lazy DOM node 

document is more effective 

creation may lower the mem 

than a DOM representation. 

ory usage.)

Nevertheless, some imple 

mentations may implement 

techniques to lower the mem 

ory usage.)

To edit the document (pro 

To process parts of the docu 

To edit the document (pro 

cessing the in memory data 

ment (handling relevant 

cessing the in memory data 

structure)

events)

structure)

To process multiple times 

To process the document only 

To process multiple times 

(document loaded in 

once (transient flow of 

(document loaded in 

memory)

events)

memory)

Processing once the parsing is 

Stream processing (start pro 

Processing once the parsing is 

finished

cessing before the parsing is 

finished

finished, and even before the 

document is completely read)

4.4.2 Combining XML Processing Techniques

The JAXP API provides support for chaining XML processings: The JAXP

javax.xml.Source

 and 

javax.xml.Result

 interfaces constitute a standard mecha 

nism for chaining XML processings. There are implementations of these two inter 

faces for DOM, SAX, and even streams; JAXB and other XML processing

technologies, such as JDOM and dom4j, provide their own implementations as well.

Basically, XML processings can be chained according to two designs:

  The first design wraps the result of one processing step into a 

Source

 object 

that can be processed by the next step. XML processing techniques that can 

produce an in memory representation of their results, such as DOM and JAXB, 

lend themselves to this design. This design is often called  batch sequential  

because each processing step is relatively independent and each runs to com 

pletion until the next step begins.

  The second design, called  stream processing  or  pipes and filters,  creates a