Java Tips - How to traverse the DOM tree using TreeWalker

DOM interface offers a nice tool for browsing the tree. This is a TreeWalker interface. It allows to performs filtering on the node-flow, convenient navigation and saving current position for the following return. Example application below shows to traverse DOM-tree on element only using TreeWalker:


import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;



import org.w3c.dom.traversal.DocumentTraversal;

import org.w3c.dom.traversal.NodeFilter;

import org.w3c.dom.traversal.TreeWalker;



import org.w3c.dom.*;



/**

 * This sample program using tree-walker for

 * non-linear traverse of DOM-document.

 */



public class Test {

  public static void main(String[] args) {

  try {

    // load the document from a file:

    DocumentBuilderFactory factory = 

      DocumentBuilderFactory.newInstance();

    DocumentBuilder loader = factory.newDocumentBuilder();

    Document document = loader.parse("sample.xml");



    // this cast is checked on Apache implementation (Xerces):

    DocumentTraversal traversal = (DocumentTraversal) document;



    TreeWalker walker = traversal.createTreeWalker(

      document.getDocumentElement(), 

      NodeFilter.SHOW_ELEMENT, null, true);



    traverseLevel(walker, "");



  } catch (Exception ex) {

    ex.printStackTrace();

  }

  }



  private static final void traverseLevel(TreeWalker walker, 

    String indent) {

  

    // describe current node:

    Node parend = walker.getCurrentNode();

    System.out.println(indent + "- " + 

      ((Element) parend).getTagName());



    // traverse children:

    for (Node n = walker.firstChild(); n != null; 

      n = walker.nextSibling()) {

      

      traverseLevel(walker, indent + '\t');

    }



    // return position to the current (level up):

    walker.setCurrentNode(parend);

  }

}

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