XmlUtil.java

import java.util.AbstractList;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public final class XmlUtil
{
	/** Returns all descendant Elements with a given tag name, in document order. */
	public static List<Element> getElementByTagName(Document doc, String childTag)
	{
		return getElementByTagName(doc.getDocumentElement(), childTag);
	}

	/** Same as {@link #getElementsByTagName(Document, String)} */
	public static List<Element> getElementByTagName(Element el, String childTag)
	{
		final NodeList nodeList = el.getElementsByTagName(childTag);
		return new AbstractList<Element>()
		{
			private final int size = nodeList.getLength();

			@Override
			public Element get(int index)
			{
				if (index < 0 || index >= size)
					throw new IndexOutOfBoundsException("index: " + index + ", size: " + size);
				return (Element) nodeList.item(index);
			}

			@Override
			public int size()
			{
				return size;
			}
		};
	}

	public static Iterable<Node> asIterable(NodeList nodeList)
	{
		return new Iterable<Node>()
		{
			@Override
			public Iterator<Node> iterator()
			{
				return new Iterator<Node>()
				{
					final int size = nodeList.getLength();
					int index;

					@Override
					public boolean hasNext()
					{
						return index < size;
					}

					@Override
					public Node next()
					{
						if (!hasNext())
							throw new NoSuchElementException();
						return nodeList.item(index);
					}
				};
			}
		};
	}

	/**
	 * @param exactDepth
	 *          should be > 0
	 */
	public static List<Element> getElementsByTagName(Document doc, String tagName, int exactDepth)
	{
		return getElementsByTagName(doc.getDocumentElement(), tagName, exactDepth);
	}

	/**
	 * @param exactDepth
	 *          should be > 0
	 */
	public static List<Element> getElementsByTagName(Element el, String tagName, int exactDepth)
	{
		if (exactDepth < 1)
			throw new IllegalArgumentException("Invalid depth: " + exactDepth);
		List<Element> elements = new ArrayList<Element>();
		updateElementsByTagName(el, tagName, 1, exactDepth, elements);
		return elements;
	}

	private static void updateElementsByTagName(Element el, String tagName, int currentDepth, int targetDepth, List<Element> elements)
	{
		Iterable<Node> childNodes = asIterable(el.getChildNodes());
		if (currentDepth < targetDepth)
		{
			int cd = currentDepth + 1;
			for (Node node : childNodes)
				if (node.getNodeType() == Node.ELEMENT_NODE)
					updateElementsByTagName((Element) node, tagName, cd, targetDepth, elements);
		}
		else
		{
			for (Node node : childNodes)
				if (node.getNodeType() == Node.ELEMENT_NODE && node.getNodeName().equals(tagName))
					elements.add((Element) node);
		}
	}

	public static String getFirstChildElementContent(Element el, String childTag)
	{
		return el.getElementsByTagName(childTag).item(0).getTextContent();
	}
}