Searching an XML file and using getNextSibling()

Question

I apologise if this question has been answered before, but I haven't been able to find a precise answer to my problem.
Here is a snippet of my XML file:
<organization...>
<title>
<item...>
<title>
<adlcp:prerequisites>
What I want to do is search this file based on item title (org->item->title). When I find the corresponding entry, I want to traverse back up the tree to retrieve an attribute of the <item> tag, the <title> belonging to the organisation, and I also want to record the sibling node <adlcp:prerequisites>.
I have no trouble obtaining traversing up the tree from the item <title>, but as soon as I try calling getFirstChild() or getNextSibling(), my method throws an exception.
Here is an excerpt of my (somewhat shoddy) code:
try
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
     docScorm = db.parse(strScorm);
     Element root = docScorm.getDocumentElement();
     NodeList children = root.getChildNodes();
     int n = children.getLength();
     String strTopicName = "";
     int i = 0 ;
     Node genericNode = null ;
     Node topicNode = null ;
     while(i < n)
          NodeList topicList = docScorm.getElementsByTagName("title");
          genericNode = topicList.item(i);
          strTopicName = genericNode.getFirstChild().getNodeValue();
          if (strTopicName.equals(strTopic))
               topicNode = topicList.item(i) ;
          i++ ;
     //Save the information in the ScormInfo object.
     siItem.setTitle(strTopicName) ;
     //We have the topic name - get the other info.
     if (topicNode != null)
          Node itemNode = topicNode.getParentNode() ;
          NamedNodeMap nnmItemAtt = itemNode.getAttributes() ;
          Node itemIdentifierNode = nnmItemAtt.getNamedItem("identifier") ;
          //Fill in the ScormInfo object details.
          siItem.setIdentifier(itemIdentifierNode.getFirstChild().getNodeValue()) ;
//I'd given up getting the organisation title, and settled for the identifier attribute instead.
Node orgNode = itemNode.getParentNode() ;
          NamedNodeMap nnmOrgAtt = orgNode.getAttributes() ;
          Node orgTitleNode = nnmOrgAtt.getNamedItem("identifier") ;
          siItem.setOrganisation(orgTitleNode.getFirstChild().getNodeValue()) ;
          //Try to get the sibling.
          Node preReqNode = topicNode.getNextSibling() ;
====================================
And this is the point where it all goes wrong. Can anyone shed some light on what I am doing wrong? Any help would be greatly appreciated.

Answer 1

After a little more debugging, I discovered that you are correct - trying to access the Node is throwing a NullPointerException, and admittedly, I was not accounting for that.
However, while I can easily take care of a NullPointerException, I am still bewildered as to why the getNextSibling function returns null in the first place. A quick snippet of the file in question shows:
<organisation...>
__<item identifier="ITEM-4E83F4CA-B846-67E5-48F1-C58732D13615" isvisible="true" identifierref="RES-74A66825-6926-3C1E-5D19-489856C9C280">
____<title>Topic_2_parallel_and_serial</title>
____<adlcp:prerequisites type="aicc_script">ITEM-5BE1806E-C38C-89A9-F2FC-BB51109259E3</adlcp:prerequisites>
__</item>
====================================
Considering my Node "topicNode" points to the "<title>Topic_2_parallel_and_serial</title> node, I am confused as to why getNextSibling does not return the <adlcp...> node. Is it not the next direct sibling?