XML traversal in levelorder

Thread view:

C. Rühl - 05 Dec 2007 13:53 GMT

Hi,

I would like to traverse a XML document in levelorder. My next steps
depend on different nodes and their levels.

What I did by now was to set up a XmlStreamEventReader to easily
choose the next steps for each node and node-type:

m_in = new FileInputStream(file);
m_factory = XMLInputFactory.newInstance();
m_parser =
m_factory.createXMLEventReader(m_in);

// parse events
while(this.m_parser.hasNext())
{
XMLEvent event = m_parser.nextEvent();

switch(event.getEventType())
{
case
XMLStreamConstants.START_DOCUMENT:
break;

case XMLStreamConstants.START_ELEMENT:
                    StartElement startElement = event.asStartElement();

                    // common mib files
                    if(startElement.getName().toString()=="Common")
                        newCommonInstance(startElement);

...

The XmlStreamEventReader traverses the XML file in preorder.

And because of my XML file only consists of nodes with attributes (so
there's no node-value only attributes an their values), working with a
DOM is pretty strange. As soon as I walk through the nodes my root has
i.e. 5 instead of actually 2 children:

root
#text
node1
#text
node2
#text

How do I get rid of the "#text"-blanks or what should I do to
correctly traverse in levelorder?

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C. Rühl - 06 Dec 2007 10:16 GMT

Okay, I just started over from scratch. I'm parsing the file now into
a DOM and give the XML root node to a method like shown here:

private void visitNodes(Node node)
{
    try
    {
        // child nodes of current node
        NodeList nodeList = node.getChildNodes();

        // loop through child nodes
        for(int i=0; i<nodeList.getLength(); i++)
        {
            if(nodeList.item(i).getLocalName()=="Component")
            {
                System.out.println(nodeList.item(i).getLocalName());
            }
        }
    }
    catch(Exception ex)
    {
        // nothing yet
    }
}

But XML level-order traversal ain't that easy... How and where can I
now insert a recursive call of that method? I can't just put it into
the for-loop, because then I get pre-ordered results. So what should I
do to traverse my file in level-order (breadth-first)?

I hope that someone gives me a little help here. Thanks a lot!

The XML file looks a little like this:

<Component>
<Component>
<Component/>
<Component/>
</Component>
<Component/>
</Component>

Reply to this Message

C. Rühl - 06 Dec 2007 12:38 GMT

Solution found:

Queue q = new Queue();
            q.enqueue(node);

            while(!q.isEmpty())
            {
                node = (Node) q.dequeue();

                if(node.getLocalName()=="TopLevelComponent"
                    || node.getLocalName()=="Component"
                    || node.getLocalName()=="SubComponent")
                {
                    System.out.println(node.getAttributes().item(2).getNodeValue() +
m_mncn);
                    m_mncn++;
                }

                NodeList children = node.getChildNodes();

                for(int i=0; i<children.getLength(); i++)
                    q.enqueue(children.item(i));
            }

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XML traversal in levelorder

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