JAVA API FOR XML DOM

Introduction

Java WSDP: Java Web Services Developer Pack

Document-oriented Java API are:– Java API for XML Processing (JAXP)

processes XML documents using various parsers

– Java Architecture for XML Binding (JAXB) processes XML documents using schema-

derived JavaBeans component classes

DOM Classes and Interfaces

Class/Interface Description

Document interface Represents the XML document’s top-level node, which provides access to all the document’s nodes—including the root element.

Node interface Represents an XML document node.

NodeList interface Represents a read-only list of Node objects.

Element interface Represents an element node. Derives from Node.

Attr interface Represents an attribute node. Derives from Node.

CharacterData interface Represents character data. Derives from Node.

Text interface Represents a text node. Derives fromCharacterData.

DOM API of JAXP

Package Description

org.w3c.dom Defines the DOM programming interfaces for XML documents, as specified by the W3C.

javax.xml.parsers

Provides classes related to parsing an XML document.DocumentBuilderFactory class and the DocumentBuilder class,returns an object that implements the W3C Document interface. This package also defines the ParserConfigurationException class forreporting errors.

Outline

XML Doc.

Document Builder

Document Builder Factory

DOM

Simple DOM program, I

import javax.xml.parsers.*;

import org.w3c.dom.*;

public class SecondDom { public static void main(String args[]) { try { ...Main part of program goes here... } catch (Exception e) { e.printStackTrace(System.out); } }}

Simple DOM program, II

First we need to create a DOM parser, called a “DocumentBuilder”.

Class DocumentBuilder provides a standard interface to an XML parser.

The parser is created, not by a constructor, but by calling a static factory method

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

DocumentBuilder builder = factory.newDocumentBuilder();

Simple DOM program, III

The next step is to load in the XML file Here is the XML file, named hello.xml:

<?xml version="1.0"?> <display>Hello World!</display>

To read this file in, we add the following line to our program:

Document document = builder.parse("hello.xml");

Notes:– document contains the entire XML file (as a tree); it is the

Document Object Model– If you run this from the command line, your XML file should be in

the same directory as your program

Simple DOM program, IV

The following code finds the content of the root element and prints it:

Element root = document.getDocumentElement(); Node textNode = root.getFirstChild(); System.out.println(textNode.getNodeValue());

The output of the program is: Hello World!

Reading in the tree

The parse method reads in the entire XML document and represents it as a tree in memory

If parsing is successful, a Document object is returned that contains nodes representing

each part of the intro.xml document.– If you want to interact with your program while it is

parsing, you need to parse in a separate thread» Once parsing starts, you cannot interrupt or stop it» Do not try to access the parse tree until parsing is done

An XML parse tree may require up to ten times as much memory as the original XML document

Other required Packages

Package Description

com.sun.xml.tree contains classes and interfaces from Sun Microsystem’sinternal XML API, which provides features currently not available in the XML 1.0 recommendation

org.xml.sax provides the Simple API for XML programmatic interface. A DOM-based parser may use an event-based implementation (such as Simple API for XML) to help create the tree structure in memory.

intro.xml

<?xml version = "1.0"?>

<!-- Fig. 8.12 : intro.xml -->

<!-- Simple introduction to XML markup -->

<!DOCTYPE myMessage [

<!ELEMENT myMessage ( message )>

<!ELEMENT message ( #PCDATA )>

]>

<myMessage>

<message>Welcome to XML!</message>

</myMessage>

MODIFYING XML DOCUMENT WITH DOM

import java.io.*;import org.w3c.dom.*;import javax.xml.parsers.*;import com.sun.xml.tree.XmlDocument;import org.xml.sax.*;

public class ReplaceText {

private Document document; public ReplaceText() { try { // obtain the default parser DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); // set the parser to validating factory.setValidating( true );

DocumentBuilder builder = factory.newDocumentBuilder();

// set error handler for errors related to parsing

builder.setErrorHandler( new MyErrorHandler() );

// obtain document object from XML document document = builder.parse(

new File( "intro.xml" ) );

// fetch the root node Node root =

document.getDocumentElement();

if ( root.getNodeType() == Node.ELEMENT_NODE ) {

Element myMessageNode = ( Element ) root; NodeList messageNodes =

myMessageNode.getElementsByTagName( "message" );

if ( messageNodes.getLength() != 0 ) {//item() returns type Object and need casting

Node message = messageNodes.item( 0 ); // create a text node Text newText =

document.createTextNode("New Message!!" );

Cast root node as element (subclass), then get list of all

message elements

// get the old text node Text oldText =

( Text )message.getChildNodes().item( 0 ); // replace the text message.replaceChild( newText, oldText }} //Write new XML document to intro1.xml( (XmlDocument) document).write( new FileOutputStream("intro1.xml" ) ); }

catch ( SAXParseException spe ) { System.err.println( "Parse error: " + spe.getMessage() ); System.exit( 1 ); } catch ( SAXException se ) { se.printStackTrace(); } catch ( FileNotFoundException fne ) { System.err.println( “XML File not found. " ); System.exit( 1 ); } catch ( Exception e ) { e.printStackTrace(); } }

public static void main( String args[] ) { ReplaceText d = new ReplaceText(); }}

Building an XML Document with DOM

Desired Output<root> <!--This is a simple contact list--> <contact gender="F"> <FirstName>Sue</FirstName> <LastName>Green</LastName> </contact> <?myInstruction action silent?> <![CDATA[I can add <, >, and ?]]></root>

import java.io.*;import org.w3c.dom.*;import org.xml.sax.*;import javax.xml.parsers.*;import com.sun.xml.tree.XmlDocument;

public class BuildXml { private Document document;

public BuildXml() { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

try { // get DocumentBuilder DocumentBuilder builder = factory.newDocumentBuilder(); // create root node document = builder.newDocument(); } catch ( ParserConfigurationException pce ) { pce.printStackTrace(); }

Element root = document.createElement( "root" );

document.appendChild( root ); Comment simpleComment =document.createComment(

"This is a simple contact list" ); root.appendChild( simpleComment );

Node contactNode = createContactNode( document );

root.appendChild( contactNode ); ProcessingInstruction pi = document.createProcessingInstruction( "myInstruction", "action silent" );

root.appendChild( pi ); CDATASection cdata =

document.createCDATASection( "I can add <, >, and ?" ); root.appendChild( cdata );

try { // write the XML document to a file

( (XmlDocument) document).write( new

FileOutputStream("myDocument.xml" ) ); } catch ( IOException ioe ) { ioe.printStackTrace(); } }

public Node createContactNode( Document document ) { Element firstName =

document.createElement( "FirstName" ); firstName.appendChild(

document.createTextNode( "Sue" ) ); Element lastName =

document.createElement( "LastName" ); lastName.appendChild(

document.createTextNode( "Green" ) ); Element contact =

document.createElement( "contact" );Attr genderAttribute =

document.createAttribute( "gender" ); genderAttribute.setValue( "F" ); contact.setAttributeNode( genderAttribute ); contact.appendChild( firstName ); contact.appendChild( lastName ); return contact; }

public static void main( String args[] ) { BuildXml buildXml = new BuildXml(); }}

Traversing the DOM

import org.w3c.dom.*;import org.xml.sax.*;import javax.xml.parsers.*;import com.sun.xml.tree.XmlDocument;

public class TraverseDOM { private Document document; public TraverseDOM( String file ) { try {

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

factory.setValidating( true ); DocumentBuilder builder =

factory.newDocumentBuilder();builder.setErrorHandler( new MyErrorHandler() );

document = builder.parse( new File( file ) ); processNode( document ); } catch ( SAXParseException spe ) { System.err.println("Parse error: " +

spe.getMessage() ); System.exit( 1 ); } catch ( SAXException se ) { se.printStackTrace(); } catch ( FileNotFoundException fne ) { System.err.println( "File not found. " ); System.exit( 1 ); } catch ( Exception e ) { e.printStackTrace();} }

public void processNode( Node currentNode ){ switch ( currentNode.getNodeType() ) {

case Node.DOCUMENT_NODE: Document doc = ( Document ) currentNode; System.out.println( Document node: " + doc.getNodeName() +

"\nRoot element: " + doc.getDocumentElement().getNodeName() );

processChildNodes( doc.getChildNodes() );

break;

case Node.ELEMENT_NODE: System.out.println( "\nElement node: " +

currentNode.getNodeName() );

NamedNodeMap attributeNodes = currentNode.getAttributes();

for (int i=0;i<attributeNodes.getLength();i++){

Attr attribute=(Attr)attributeNodes.item( i );

System.out.println( "\tAttribute: " + attribute.getNodeName() + " ;Value = "

attribute.getNodeValue() )

}

processChildNodes( currentNode.getChildNodes() );

break;

case Node.CDATA_SECTION_NODE: case Node.TEXT_NODE: Text text = ( Text ) currentNode; if ( !text.getNodeValue().trim().equals( "" ) ) System.out.println( "\tText: " +

text.getNodeValue() ); break; }}

public void processChildNodes( NodeList children ) { if ( children.getLength() != 0 ) for ( int i=0;i<children.getLength();i++) processNode(children.item(i) ); }

public static void main( String args[] ) { if ( args.length < 1 ) { System.err.println("Usage: java

TraverseDOM <filename>" ); System.exit( 1 ); } TraverseDOM traverseDOM = new

TraverseDOM( args[ 0 ] ); }}