Definition

DOM

Tree based Parser

Node Interface

Loading an XMLDocument

import javax.xml.parsers.*;
import org.w3c.dom. *;
public class Course {public static void main(String[] args) throws Exception {
//factory instantiation: API that enables applications to obtain a parser that
//produces DOM object trees from XML documents
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
//validation and namespaces
factory.setValidating(true);
factory.setNamespaceAware(true);
//parser instantiation
//API to obtain DOM document instances from XML documents
DocumentBuilder builder = factory.newDocumentBuilder();
//install ErrorHandler
builder.setErrorHandler(new MyErrorHandler());
//parsing instantiation (code below is written from this line onwards)
Document coursedoc = builder.parse(args[0]);
}
}

The Node interface is the datatype of the entire DOM.

Example

Node Interface

Document Methods (child interface of Node)

Element Methods (child interface of Node)

Attr Methods (child interface of Node)

Example

<?xml version="1.0"?>
<courses>
<course semester="Summer">
<title> Semi-structured Data (SSD) </title>
<day> Thursday </day>
<time> 09:15 </time>
<location> HS8 </location>
</course>
</courses>

courses:
course: semester="Summer"
title: "Semi-structured Data (SSD)"
day: "Thursday"
time: "09:15"
location: "HS8"

• Reading document

  import jave.io.*;
  import javax.xml.parsers.*;
  import org.w3c.dom. *;public class Course {public static void main(String[] args) throws Exception {
  // ... see above ...Document coursedoc = builder.parse(args[0]);//call visit node starting from the root node
  visitNode(coursedoc.getDocumentElement());
  }//the recursive method visitNode
  private static void visitNode(Node node) {
  //element nodes
  if (node.getNodeType() == Node.ELEMENT_NODE) {
  System.out.print("\n" + node.getNodeName() + ": ");
  NamedNodeMap attributes = node.getAttributes();
  if (attributes != null) {
  for (int i = 0; i < attributes.getLength(); i++) {
  System.out.print(attributes.item(i) + " ");
  }
  }
  }
  //text nodes
  if (node.getNodeType() == Node.TEXT_NODE && !node.getTextContent().trim().isEmpty()) {
  System.out.print("\"" + node.getTextContent().trim() + "\"");
  }
  // visit child nodes
  NodeList nodelist = node.getChildNodes();
  for (int i = 0; i < nodelist.getLength(); i++) {
  visitNode(nodelist.item(i));
  }
  }
  }

• Create and validate document

  import java.io.File;
  import javax.xml.parsers.*;
  import javax.xml.transform.*;
  import javax.xml.transform.dom.DOMSource;
  import javax.xml.transform.stream.StreamResult;
  import org.w3c.dom.*;
  public class Course {public static void main(String[] args) throws Exception {
  // ... see above .../*
  * CREATE DOCUMENT
  */
  Document coursedoc = builder.newDocument();//create all the necessary elements
  Element courses = coursedoc.createElement("courses");
  Element course = coursedoc.createElement("course");
  course.setAttribute("semester", "Summer");
  Element title = coursedoc.createElement("title");
  title.setTextContent("Semi-structured Data (SSD)");//append the children in a bottom-up-order
  course.appendChild(title); course.appendChild(day);
  course.appendChild(time); course.appendChild(location);
  courses.appendChild(course);
  coursedoc.appendChild(courses);/*
  * VALIDATE
  */
  //validate the new document against a schema
  //load XML Schema
  File schemaFile = new File("schema.xsd");
  SchemaFactory factory= SchemaFactory(XMLConstants.W3C_XML_SCHEMA_NS_URI);
  Schema schema = schemaFactory.newSchema(schemaFile);
  // Create Validator and validate
  Validator validator = schema.newValidator();
  try{
  validator.validate(new DOMSource(coursedoc));
  } catch (SAXException ex) {
  exit("Created document not valid:" + ex.getMessage());
  }/*
  * WRITE INTO A FILE
  */
  //write the document into a file
  //factory instantiation
  TransformerFactory tfactory = TransformerFactory.newInstance();
  //transformer instantiation
  Transformer transformer = tfactory.newTransformer();
  //create a new input XML source
  DOMSource source = new DOMSource(coursedoc);
  //construct a stream result
  StreamResult result = new StreamResult(new File("courses.xml"));
  //actual transformation
  transformer.transform(source, result);
  System.out.println("File saved!");
  }
  }