code: private void writeSimpleField(XMLStreamWriter xmlOut, String columnName, String columnType) throws XMLStreamException {
          xmlOut.writeStartElement("SimpleField");
          xmlOut.writeAttribute("name", columnName);
          xmlOut.writeAttribute("type", columnType);
          xmlOut.writeEndElement();//Write schema
      }
docs: The declaration of the custom field, which must specify both the type and
  the name of this field. If either the type or the name is omitted, the
  field is ignored. The type can be one of the following : string, int,
  uint, short, ushort, float, double, bool.
  
  Syntax :
  
  <SimpleField type="string" name="string">
  
  @param xmlOut
  @param columnName
  @param columnType
  @throws XMLStreamException