Question

If there is an XML file called a.xml, is there any way to traverse its DOM tree in
postorder fashion?

I tried using GetNextSiblings method but it didn’t work. Any idea?

Here is the XML:

<?xml version="1.0" encoding="UTF-8"?> 
       <title text="title1"> 
           <comment id="comment1">
               <data> abcd </data>
               <data> efgh </data>
           </comment>
           <comment id="comment2">
               <data> ijkl </data>
               <data> mnop </data>
               <data> qrst </data>
           </comment>
       </title>

And here is my code to traverse it:

import java.io.File;
import java.io.IOException;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.w3c.dom.*;
import org.w3c.dom.traversal.DocumentTraversal;
import org.w3c.dom.traversal.NodeFilter;
import org.w3c.dom.traversal.NodeIterator;
import org.xml.sax.SAXException;

public class Newtraverse {
public static Node check(Node node){
    Node c=node;
    // Node c = null;
    if (node!=null)
        if (node.hasChildNodes()==true &&node.getNodeName()!=null)
        {
            node=node.getFirstChild().getNextSibling();
            if (node!=null)
            {
                 System.out.println(node);

                 check(node); 
            }

            if(node==null)
            {
                c=c.getNextSibling();
                check(c);
            }
       }

    return node;
 }
    public static void main(String[] args) throws ParserConfigurationException, SAXException, IOException {
        File file = new File("d:\\a.xml");
  DocumentBuilderFactory dbf =
  DocumentBuilderFactory.newInstance();
  DocumentBuilder db = dbf.newDocumentBuilder();
  Document document = db.parse(file);
  document.getDocumentElement().normalize();


  Node b=document.getFirstChild();

 Node result= check(b);
}
}

And here is the output:

[comment: null]
[data: null]

As you all can see, it just traverses two tags. How can I fix this?

Answer 1

Here’s how your check method should like (I didn’t run it though…)

public static void check(Node node){
  if (node == null || node.getNodeName() == null)
    return;

  // Do PostOrder on all children
  check(node.getFirstChild());  

  // Now that all children were traversed, process the current node:
  System.out.println(node); 

  // Do PostOrder on following siblings
  check(node.getNextSibling();  
}