Reimporting exported XML using DOM

Question

Hi,
I'm trying to set up an import/export for a data structure, 'SimpleNode' created by a JavaCC parser for classical propositional logic.
SimpleNode implements Node, and have the following attributes
protected SimpleNode parent;
protected SimpleNode[] children;
protected int id;
protected LogicParser parser;
protected String label;
...So nothing too special there.
A simple representation of the sentence
a OR (b AND c) IMPLIES NOT(D)
"a | (b & c) => !d"
Is represented as a tree with in the following manner
Root
Imp
  Or
   Atom a
   And
    Atom b
    Atom c
  Not
   Atom dWhich is all fine.
I've written something to export to an XML structure which gives the following output for the above sentence
<IMPLIES>
  <NOT>
    <TRUE/>
  </NOT>
  <IMPLIES>
    <OR>
      <ATOM>a</ATOM>
      <ATOM>b</ATOM>
    </OR>
    <NOT>
      <ATOM>c</ATOM>
    </NOT>
  </IMPLIES>
</IMPLIES>Which again, seems fine.
The problem is then when I'm trying to reimport the XML and create a SimpleNode from it.
Using the following code
     public static void main(String[] args) {
          // if (args.length <= 0) {
          // System.out.println("Usage: java DOMCommentReader URL");
          // return;
          String url = "propLogic.xml";
          try {
               DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
               DocumentBuilder parser = factory.newDocumentBuilder();
               // Check for the traversal module
               DOMImplementation impl = parser.getDOMImplementation();
               if (!impl.hasFeature("traversal", "2.0")) {
                    System.out.println("A DOM implementation that supports traversal is required.");
                    return;
               // Read the document
               Document doc = parser.parse(url);
               // Create the TreeWalker
               DocumentTraversal traversable = (DocumentTraversal) doc;
               // Taken from
               // http://www.oreilly.com/catalog/jenut2/chapter/ch19.html
               NodeFilter filter = new NodeFilter() {
                    public short acceptNode(Node n) {
                         if (n.getNodeType() == Node.TEXT_NODE) {
                              // Use trim() to strip off leading and trailing space.
                              // If nothing is left, then reject the node
                              if (((Text) n).getData().trim().length() == 0)
                                   return NodeFilter.FILTER_REJECT;
                              // if (n.getParentNode().getNodeName() != "ATOM")
                              // return NodeFilter.FILTER_REJECT;
                         return NodeFilter.FILTER_ACCEPT;
               int whatToShow = (NodeFilter.SHOW_ELEMENT + NodeFilter.SHOW_TEXT);
               TreeWalker iterator = traversable.createTreeWalker(doc, whatToShow, filter, true);
               printElements(iterator, 0);
          } catch (SAXException e) {
               System.out.println(e);
               System.out.println(url + " is not well-formed.");
          } catch (IOException e) {
               System.out.println("Due to an IOException, the parser could not check " + url);
          } catch (FactoryConfigurationError e) {
               System.out.println("Could not locate a factory class");
          } catch (ParserConfigurationException e) {
               System.out.println("Could not locate a JAXP parser");
     public static void printElements(TreeWalker iterator, int depth) {
          Node n = iterator.getCurrentNode();
          n.normalize();
          String indent = new String();
          for (int i = 0; i < depth; i++) {
               indent += "  ";
          depth++;
          System.out.print(indent + n.getNodeName() + " " + n.getNodeValue());
//          if (n.getParentNode() != null)
//               System.out.print(" (parent is " + n.getParentNode().getNodeName() + ")");
          System.out.println();
          for (Node child = iterator.firstChild(); child != null; child = iterator.nextSibling()) {
               printElements(iterator, depth);
          iterator.setCurrentNode(n);
     }I can get a correct looking representation of the structure
#document null
  IMPLIES null
    NOT null
      TRUE null
    IMPLIES null
      OR null
        ATOM null
          #text a
        ATOM null
          #text b
      NOT null
        ATOM null
          #text cBut I'm having trouble using the Iterator to create SimpleNodes from the Nodes
All a SimpleNode needs is a type (an integer representing whether the operator is AND, OR, NOT, IMPLIES etc)
and a label, which can be null or in the case of an ATOM will have the atom name, "a", "b", "c" etc.
A SimpleNode is easily created with the constructor
SimpleNode foo = new SimpleNode(type);
foo.setLabel("a");
and adding a child by
foo.jjtAddChild(SimpleNode n, int i)
where i is the number of the child.
Hopefully I've not rambled too much and it makes sense.
If anyone can give me any pointers or some code/pseudocode to pick through then it'd be much appreciated.
Duncan

Answer 1

No bother, tweaked the printElements to fix.