Writing Enterprise Applications with Java™ 2 SDK, Enterprise Edition phần 9 potx

LESSON 6 EXTENSIBLE MARKUP LANGUAGE (XML)

SEPTEMBER 27, 2000 95

The APIs

The j2ee.jar file that comes with your J2EE installation provides APIs for parsing and

manipulating XML data. The JAR file currently provides SAX, DOM, and J2EE XML APIs.

You can use whichever API best suits your needs because as shown in Figure 22, XML text

is independent of the platform and language of its creation..

Figure 22 Platform and Language Neutral Text

SAX and DOM

The SAX API is an event-driven, serial-access mechanism that does element by element pro￾cessing.

The DOM API provides a relatively familiar tree structure of objects. You can use the DOM

API to manipulate the hierarchy of application objects it encapsulates. The DOM API is

ideal for interactive applications because the entire object model is present in memory,

where it can be accessed and manipulated by the user.

Constructing the DOM requires reading the entire XML structure and holding the object tree

in memory, so it is much more CPU and memory intensive. For that reason, the SAX API

will tend to be preferred for server-side applications and data filters that do not require an in￾memory representation of the data.

Note: You can find more information on the DOM and SAX APIs at this location:

http://java.sun.com/xml/docs/tutorial/overview/3_apis.html

J2EE

The platform-independent J2EE XML APIs use a DOM tree and provide a wealth of meth￾ods for manipulating the DOM hierarchy. The J2EE XML APIs are in the package com.sun

and were used in this lesson’s example. Please note that these APIs are subject to change.

Application written in

Java programming

language running on

Unix.

Application written in

C++ running on

Windows.

DOM SAX

XML

HTTP

DTD