JAXP API using DOM Parser

In the previous issue of Java Jazz Up, you have read about the JAXP APIs and learned how an XML document is parsed using the serially access mode (SAX) parser. Now you will learn how the DOM parser works with the same xml document. Lets quickly focus on the overview
of XML parser.

Introduction to XML Parser:

In computing terms, a parser is a program that takes input in the form of sequential instructions, tags, or some other defined sequence of tokens, and breaks them up into
easily manageable parts. XML parser is used to read, update, create and manipulate an XML document. Whenever the XML document executes, the parser recognizes and responds to each XML structure taking
some specified action based on the structure type.

XML parsers can be validating or nonvalidating. Validating parser checks the contents of a document against a set of specific rules i.e. in what order they must appear. These rules appear in an XML document either as an optional XML structure called a document type definition,
or DTD, or as an XML Schema.

Nonvalidating parsers are smaller and faster, but they do not check documents against the DTD. They only check whether the XML document is structurally well formed or not. Parsing XML Documents

To manipulate an XML document, XML parser is needed. The parser loads the document into the computer’s memory. Once the document is loaded, its data can be manipulated using the appropriate parser.

In this section, we will discuss about DOM parsers of JAXP APIs and for accessing XML documents in random access mode. The specifications to ensure the validity of XML documents are DTDs and the Schemas.

DOM (Document Object Model)

The XML Document Object Model (XML DOM) defines a standard way to access and manipulate XML documents using any programming language (and a parser for that


The DOM presents an XML document as a treestructure (a node tree), with the elements, attributes, and text defined as nodes. DOM provides access to the information stored in your XML document as a hierarchical object model.

The DOM converts an XML document into a collection of objects in an object model in a tree structure (which can be manipulated in any way). The textual information in XML document gets turned into a bunch of tree nodes and a user can easily traverse through any part of the object tree, any time. This makes easier to modify the data, to remove it, or even to insert a new one. This mechanism is also known as the random access protocol.

DOM is very useful when the document is small. DOM reads the entire XML structure and holds the object tree in memory, so it is much more CPU and memory intensive. The DOM is most suited for interactive applications because the entire object model is present in memory, where it can be accessed and manipulated by the user.

The Document Object Model implementation is defined in the following packages:

JAXP APIs Description
org.w3c.dom Defines the Document class (a DOM) along with the classes for all of the
components of a DOM.
javax.xml.parsers The JAXP APIs provide a common interface for different vendors’ to use
SAX and DOM parsers.

The DOM API is defined in org.w3c.dom package of JAXP-APIs. The DOM API is easier to use. It provides a tree structure of objects. The DOM API is used to manipulate the hierarchy of application objects it encapsulates.

Mar 2008 | Java Jazz Up | 18
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