From: James Henderson <JamesHenderson_at_CORSOF.COM>
Date: Tue, 04 Mar 2003 08:04:48 -0700

I'm trying to unmarshall a DOM node to an XML file using JAXB. However I keep receiving a NullPointerException. This only seems to occur when I create the DOM Node from scratch. The stack trace looks like the following:

java.lang.NullPointerException
        at com.sun.xml.bind.unmarshaller.SAXUnmarshallerHandlerImpl.startElement
(SAXUnmarshallerHandlerImpl.java:87)
        at com.sun.xml.bind.unmarshaller.DOMScanner.visit(DOMScanner.java:109)
        at com.sun.xml.bind.unmarshaller.DOMScanner.parse(DOMScanner.java:64)
        at com.sun.xml.bind.unmarshaller.UnmarshallerImpl.unmarshal(Unmarshaller
Impl.java:149)
        at Main.main(Main.java:103)


(If I unmarshal an XML file into a DOM node, I can successfully marshall the DOM node out to a new XML file using JAXB without error.)


Any insight into what I am doing wrong would be greatly appreciated!


Sample code and XSD follow...

Sample Code:

import itemlistsample.*;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Text;



public class Main
{

  public static void main(String[] args)
  {

      try
      {
          JAXBContext jc = JAXBContext.newInstance( "itemlistsample" );
          Unmarshaller u = jc.createUnmarshaller();


          /*
          * Set up DOM Node Document Object.
          */

          DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
          dbf.setNamespaceAware(true);
          DocumentBuilder db = dbf.newDocumentBuilder();
          Document doc = db.newDocument();



          System.out.println();
          System.out.println();
          System.out.println("Create a DOM Node and unmarshall to an XML file");


          /*
          * Generate elements within DOM document
          */
          Element itemListElt = (Element)doc.createElement("item_list");
          Element itemInfo = (Element)doc.createElement("item_info");
          Element name = (Element)doc.createElement("name");
          Element price = (Element)doc.createElement("price");


          /*
          * 3-Ring Binder @ 4.99
          */
          name.appendChild(doc.createTextNode("3-Ring Binder"));
          itemInfo.appendChild(name);

          price.appendChild(doc.createTextNode("4.99"));
          itemInfo.appendChild(price);
          itemListElt.appendChild(itemInfo);


          /*
          * Large Paper Clips @ 1.23
          */


          itemInfo = (Element)doc.createElement("item_info");
          name = (Element)doc.createElement("name");
          price = (Element)doc.createElement("price");
          name.appendChild(doc.createTextNode("Large Paper Clips"));
          itemInfo.appendChild(name);

          price.appendChild(doc.createTextNode("1.23"));
          itemInfo.appendChild(price);

          itemListElt.appendChild(itemInfo);
          doc.appendChild(itemListElt);



          /*
          * Display DOM document as a sanity check
          */

          itemListElt = doc.getDocumentElement();
          System.out.println(itemListElt.getTagName());

          NodeList nl = itemListElt.getElementsByTagName("item_info");
          traverse(" ", nl.item(0));



          /*
          * Use JAXB to unmarshal the DOM document into
          * an instance of the generated JAXB class for
          * the root element. >>>Stack trace occurs here!<<<
          */
          ItemListType il = (ItemListType)u.unmarshal(doc);




          /*
          * Marshal to an XML file
          */
          Marshaller m = jc.createMarshaller();
          m.setProperty( Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE );
          m.marshal( il, new FileOutputStream("item_new.xml") );

      }
      catch (Exception e)
      {
 e.printStackTrace();
      }
  }

  public static void traverse(String indent, Node n)
  {
    if (n != null)
    {
      if (n.getNodeName() != null)
      {
        System.out.println(indent + n.getNodeName());
        traverse(indent + " ", n.getFirstChild());
      }

      if (n.getNodeValue() != null)
      {
        System.out.println(indent + n.getNodeValue());
      }
      traverse(indent, n.getNextSibling());
    }
  }
}



Sample XSD:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
 <xsd:element name="item_list" type="ItemListType"/>
 <xsd:complexType name="ItemListType">
  <xsd:sequence>
   <xsd:element name="item_info" type="ItemInfoType" maxOccurs="unbounded"/>
  </xsd:sequence>
 </xsd:complexType>
 <xsd:complexType name="ItemInfoType">
  <xsd:sequence>
   <xsd:element name="name" type="xsd:string"/>
   <xsd:element name="price" type="xsd:double"/>
  </xsd:sequence>
 </xsd:complexType>
</xsd:schema>