DOM (xml) question

[jefff willis]

Whenever I build a Document by parsing an XML file, I have no problems getting the root node with a call to getDocumentElement().

However, if I construct a Document in my application, and I search for that Documents root node, the method returns a null.

Here is a complete app:

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

public class DocTest
{
 
  public DocTest()
  {
    Document fileDocument = buildDocument ("test.xml");
    Document appDocument  = null;
 
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    try
    {
      DocumentBuilder builder = factory.newDocumentBuilder();
 
      Element root;
 
      appDocument = builder.newDocument();
      root = createXMLElement(appDocument, "testRoot");
      root.appendChild( createXMLElement(appDocument, "testData", "goes here") );
 
    }
    catch(ParserConfigurationException  ex)
    {
      System.err.println("Failed to create CXB document: " + ex);
    }
    catch(DOMException de)
    {
      System.err.println("(creating CXB) DOM Exception: " + de);
    }
    System.out.println("app  XML root = " +  showRoot( appDocument ) );
    System.out.println("file XML root = " +  showRoot( fileDocument ) );
 
  }
 
  public String showRoot( Document doc)
  {
    Element root = doc.getDocumentElement();
 
    if (root == null)
      return "(null)";
 
    return root.toString();
  }
 
  public static Document buildDocument( String fileName )
  {
    Document theDocument;
 
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
 
    try
    {
      DocumentBuilder builder = factory.newDocumentBuilder();
      theDocument = builder.parse( new File(fileName) );
 
      return theDocument;
    }
    catch (SAXException sxe)
    {
 
      // Error generated during parsing
      Exception  x = sxe;
      if (sxe.getException() != null)
        x = sxe.getException();
      x.printStackTrace();
 
      } catch (ParserConfigurationException pce)
      {
        System.err.println("Parser config error:" + pce);
        // Parser with specified options can't be built
        pce.printStackTrace();
        } catch (IOException ioe)
        {
          System.err.println("IOException: " + ioe);
          // I/O error
          //ioe.printStackTrace();
        }
 
        return null;
 
  } // build document
 
  public static Element createXMLElement( Document doc, String name, String text)
  {
    Element e = doc.createElement(name);
    Text t    = doc.createTextNode( text );
    e.appendChild(t);
    return e;
  }
 
  private Element createXMLElement( Document doc, String name)
  {
    Element e = doc.createElement(name);
    return e;
  }
 
  public static void main(String[] args)
  {
    DocTest dt = new DocTest();
  }
}
 

Just for good measure, here is the test.xml file:

  
<testRoot>
<testData> goes here </testData>
</testRoot>

[Ernest Friedman-Hill]

Document.createElement() creates an element without a parent. You have to attach that element to something before it's part of a DOM tree. In particular, you have to attach one Element to a Document to be its root element:

      appDocument = builder.newDocument();
      root = createXMLElement(appDocument, "testRoot");
      root.appendChild( createXMLElement(appDocument, "testData", "goes here") );
      [B]appDocument.appendChild(root);[/B]

Now the output will be what you expect.

[jefff willis]

Yeah, that cleared it right up.

Thanks a lot.