JAXB Partial Object Parsing

JaxbPartialObjectParser.java

public class JaxbPartialObjectParser
{
  public static void main(String[] args) throws Exception
  {
    String xmlStr = "<root><student><name>Raju</name></student></root>";

    // Assuming Student class is JAXB generated

    Iterator<Student> it = extractPartialObjects(new StringReader(xmlStr), QName.valueOf("student"), Student.class);
    while (it.hasNext())
      System.out.println(it.next().getName());
  }

  /**
   * @param partialObjClass
   *          JAXB generated class which needs to be created by start parsing
   *          from tag {@code partialObjTag}
   */
  public static <T> Iterator<T> extractPartialObjects(Reader reader, QName partialObjTag, Class<T> partialObjClass)
  {
    XMLStreamReader xsr;
    Unmarshaller unmarshaller;
    try
    {
      xsr = XMLInputFactory.newInstance().createXMLStreamReader(reader);
      unmarshaller = JAXBContext.newInstance(partialObjClass).createUnmarshaller();
    }
    catch (JAXBException | XMLStreamException | FactoryConfigurationError e)
    {
      throw new RuntimeException(e.getMessage(), e);
    }

    return new Iterator<T>()
    {
      T curPartialObj;

      @Override
      public boolean hasNext()
      {
        return (curPartialObj != null) || ((curPartialObj = parseNextPartialObj()) != null);
      }

      @Override
      public T next()
      {
        if (!hasNext())
          throw new NoSuchElementException();

        T tmp = curPartialObj;
        curPartialObj = null;
        return tmp;
      }

      T parseNextPartialObj()
      {
        try
        {
          for (;; xsr.next())
          {
            if (xsr.getEventType() == XMLEvent.START_ELEMENT && xsr.getName().equals(partialObjTag))
              return unmarshaller.unmarshal(xsr, partialObjClass).getValue();
            if (!xsr.hasNext())
              break;
          }
          return null;
        }
        catch (XMLStreamException | JAXBException e)
        {
          throw new RuntimeException(e.getMessage(), e);
        }
      }
    };
  }
}