Creating a new XML document with DOM Parser and persisting the DOM Tree

The following code example demonstrates the power of the DOM Parser by creating an XML document on-the-fly with the create methods from the DOM Parser API - something that is not possible to do with a SAX Parser. The code also shows how to take a DOM Tree and convert it to a String (XML content). This String can then be persisted to an XML document file.

package info.icontraining.parsers;

import java.io.StringWriter;
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource; 
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.*;
import org.xml.sax.*;

public class DOMParserNewDocument implements ErrorHandler {
   public static void main(String[] args) throws TransformerException {

      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

      try {
         factory.setNamespaceAware(true);
         factory.setValidating(true);

         DocumentBuilder dom = factory.newDocumentBuilder();            
         dom.setErrorHandler(new DOMParserNewDocument());
         Document doc = dom.newDocument();

         Element invoiceElement = doc.createElement("Invoice");
         Attr invoiceNumberAttr = doc.createAttribute("invoice-number");
         invoiceNumberAttr.setNodeValue("123456");
         invoiceElement.setAttributeNode(invoiceNumberAttr);
         doc.appendChild(invoiceElement);

         Element dateElement = doc.createElement("date");         
         Element monthElement = doc.createElement("month");         
         Element dayElement = doc.createElement("day");
         Element yearElement = doc.createElement("year");

         monthElement.appendChild(doc.createTextNode("July"));
         dayElement.appendChild(doc.createTextNode("22"));
         yearElement.appendChild(doc.createTextNode("2011"));

         dateElement.appendChild(monthElement);          
         dateElement.appendChild(dayElement);
         dateElement.appendChild(yearElement);

         invoiceElement.appendChild(dateElement);  
         // convert DOM tree to XML string
   
         Transformer transformer =
                        TransformerFactory.newInstance().newTransformer();
         transformer.setOutputProperty(OutputKeys.INDENT, "yes");

         StreamResult result = new StreamResult(new StringWriter());
         DOMSource source = new DOMSource(doc);
         transformer.transform(source, result);

         String xmlString = result.getWriter().toString();
         System.out.println(xmlString);
     
      } catch (ParserConfigurationException e) {
         e.printStackTrace();
      } 
   }
 
   public void fatalError(SAXParseException err)
        throws SAXException {
      System.out.println("** Fatal Error"
                          + ", line " + err.getLineNumber()
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }

   public void error(SAXParseException err)        
         throws SAXParseException {
      System.out.println("** Error"
                          + ", line " + err.getLineNumber()
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }

   public void warning(SAXParseException err)         
        throws SAXParseException {
      System.out.println("** Warning"
                          + ", line " + err.getLineNumber()
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }
}

Parsing XML with a DOM Parser

The DOM Parser in the example code below is a validating parser. The parser code, processes the element, attribute and the text nodes of the document and prints them to the console (while ignoring the rest of the XML artifacts). It does not modify the XML document eventhough it maintains an in-memory representation of the XML Document.

package info.icontraining.parsers;

import java.io.IOException;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.*;

public class DOMParserWithDTD implements ErrorHandler {
 
   public static void main(String[] args) throws SAXException, IOException  {
  
      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
  
      try {
         factory.setNamespaceAware(true);
         factory.setValidating(true);
         factory.setFeature("http://apache.org/xml/features/validation/schema", true);
         factory.setIgnoringElementContentWhitespace(true);
   
         DocumentBuilder dom = factory.newDocumentBuilder();
         dom.setErrorHandler(new TestDOMParser());
         Document doc = dom.parse("Invoice.xml");
   
         processNode(doc);

      } catch (ParserConfigurationException e) {
         e.printStackTrace();
      }     
   } 
   
   private static void processNode(Node node) {

      NodeList list = node.getChildNodes();   
      for(int i=0; i<list.getLength(); i++) {
 
         if (list.item(i).getNodeType() == Node.ELEMENT_NODE) {
            processElementNode(list.item(i));
            processNode(list.item(i));
         }
   
         if (list.item(i).getNodeType() == Node.TEXT_NODE) {
            processTextNode(list.item(i));
         }
      }
   }
 
   private static void processTextNode(Node text) {  
      if (text.getNodeValue().trim().length() != 0)
         System.out.println(text.getNodeValue().trim());
   }    

   private static void processElementNode(Node element) {
  
      String temp = "";
      temp = temp + "<" + element.getNodeName();
  
      if (element.hasAttributes()) {
         NamedNodeMap map = element.getAttributes();
        
         for(int i=0; i<map.getLength(); i++) {
            temp = temp + " " + map.item(i).getNodeName();
            temp = temp + "=\"" + map.item(i).getNodeValue() + "\"";
         }
      }
  
      temp = temp + ">";
      System.out.println(temp);
   }
 
   public void fatalError(SAXParseException err) throws SAXException {

      System.out.println("** Fatal Error" 
                          + ", line " + err.getLineNumber() 
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }     

   public void error(SAXParseException err) throws SAXParseException {
      System.out.println("** Error" 
                          + ", line " + err.getLineNumber() 
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }

   public void warning(SAXParseException err) throws SAXParseException {
      System.out.println("** Warning" 
                          + ", line " + err.getLineNumber()              
                          + ", uri " + err.getSystemId());
      System.out.println(" " + err.getMessage());
   }
}