Chapter 4 XML Processing

165

equivalent XML representation is often called serialization or marshalling. Some

processing models support both processing types, but others, such as SAX, do not. 

E

Just as you would avoid manually parsing XML documents, you should avoid 

manually constructing XML documents. It is better to rely on higher level, re 

liable APIs (such as DOM, and DOM like APIs, or JAXB technology) to con 

struct XML documents, because these APIs enforce the construction of well 

formed documents. In some instances, these APIs also allow you to validate 

constructed XML documents.

Now let's take a closer look at these XML processing APIs.

4.4.1.1

SAX Programming Model

When you use SAX to process an XML document, you have to implement event

handlers to handle events generated by the parser when it encounters the various

tokens of the markup language. Because a SAX parser generates a transient flow of

these events, it is advisable to process the source document in the following fashion.

Intercept the relevant type of the events generated by the parser. You can use the

information passed as parameters of the events to help identify the relevant informa 

tion that needs to be extracted from the source document. Once extracted from the

document, the application logic can process the information.

Typically, with SAX processing, an application may have to maintain some

context so that it can logically aggregate or consolidate information from the flow

of events. Such consolidation is often done before invoking or applying the appli 

cation's logic. The developer has two choices when using SAX processing:

1. The application can  on the fly  invoke the business logic on the extracted in 

formation. That is, the logic is invoked as soon as the information is extracted 

or after only a minimal consolidation. With this approach, referred to as stream 

processing, the document can be processed in one step.

2. The application invokes the business logic after it completes parsing the docu 

ment and has completely consolidated the extracted information. This ap 

proach takes two steps to process a document.

Note that what we refer to as consolidated information may in fact be domain 

specific objects that can be directly passed to the business logic.