XML DOM

XML DOM

Document Object Model is for defining the standard for accessing and manipulating XML documents. XML DOM is used for  

Loading the xml document Accessing the xml document

Deleting the elements of xml document Changing the elements of xml document

According to the DOM, everything in an XML document is a node. It considers The entire document is a document node

Every XML element is an element node The text in the XML elements are text nodes Every attribute is an attribute node Comments are comment nodes

DOM Levels

Level 1 Core: W3C Recommendation, October 1998

o It has feature for primitive navigation and manipulation of XML trees o other Level 1 features are: All HTML features

Level 2 Core: W3C Recommendation, November 2000

o It adds Namespace support and minor new features

o other Level 2 features are: Events, Views, Style, Traversal and Range Level 3 Core: W3C Working Draft, April 2002

o It supports: Schemas, XPath, XSL, XSLT We can access and parse the XML document in two ways:

o Parsing using DOM (tree based) o Parsing using SAX (Event based)

Parsing the XML doc. using DOM methods and properties are called as tree based approach whereas using SAX (Simple Api for Xml) methods and properties are called as event based approach.

1. DOM based XML Parsing:(tree based)

JAXP is a tool, stands for Java Api for Xml Processing, used for accessing and manipulating xml document in a tree based manner.

In this approach, to access XML document, the document object model implementation is defined in the following packages:

javax.xml.parsers

org.w3c.dom

The following DOM java Classes are necessary to process the XML document: DocumentBuilderFactory class creates the instance of DocumentBuilder. DocumentBuilder produces a Document (a DOM) that conforms to the DOM

specification

The following methods and properties are necessary to process the XML document:

To Count the Elements in a XML File

This program takes a file name from the console and checks its availability. If the file exists then a parser is created using Document Builder. This object parses the given XML document. It searches the specified element name and counts its occurrence in the xml file. If the given element doesn't exist it displays the '0' element.

Step 1: Create an xml file: Employee-Detail.xml <?xml version = "1.0" ?>

<Employee-Detail> <Employee>

<Emp_Id> E-001 </Emp_Id>

<Emp_Name> Vinod </Emp_Name> <Emp_E-mail> Vinod@yahoo.com </Emp_E-mail> </Employee>

<Employee>

<Emp_Id> E-002 </Emp_Id> <Emp_Name> Arun </Emp_Name>

<Emp_E-mail> Arun@yahoo.com </Emp_E-mail> </Employee>

</Employee-Detail>

Step 2: Create a java based dom for counting the number of elements in xml file. import org.w3c.dom.*;

import javax.xml.parsers.*; import java.io.*;

public class CountNodes

{

public static void main(String[] args)

{

try

{

File file = new File(args[0]); // Employee_Detail.xml is a file to be parsed is given as //input from command prompt

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); // parser is created Document doc = builder.parse(file); // file is parsed

NodeList list = doc.getElementsByTagName(“Emp_Id”); // the element to be searched is specified

System.out.println("Number of nodes: " + list.getLength()); // counting no. of occurrences }catch (Exception e){ }

}

}

Output:

Number of nodes: 2