Can I iterate through a NodeList using for-each in Java?

Question

I want to iterate through a NodeList using a for-each loop in Java. I have it working with a for loop and a do-while loop but not for-each.

Node         


        

Answer 1

NodeList does not implement Iterable, so you cannot use it with the enhanced for loop.

Answer 2

If the current DOM element is removed (via JavaScript) while iterating a NodeList (created from getElementsByTagName() and maybe others), the element will disappear from the NodeList. This makes correct iteration of the NodeList more tricky.

public class IteratableNodeList implements Iterable<Node> {
    final NodeList nodeList;
    public IteratableNodeList(final NodeList _nodeList) {
        nodeList = _nodeList;
    }
    @Override
    public Iterator<Node> iterator() {
        return new Iterator<Node>() {
            private int index = -1;
            private Node lastNode = null;
            private boolean isCurrentReplaced() {
                return lastNode != null && index < nodeList.getLength() &&
                       lastNode != nodeList.item(index);
            }

            @Override
            public boolean hasNext() {
                return index + 1 < nodeList.getLength() || isCurrentReplaced();
            }

            @Override
            public Node next() {
                if (hasNext()) {
                    if (isCurrentReplaced()) {
                        //  It got removed by a change in the DOM.
                        lastNode = nodeList.item(index);
                    } else {
                        lastNode = nodeList.item(++index);
                    }
                    return lastNode;
                } else {
                    throw new NoSuchElementException();
                }
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }

    public Stream<Node> stream() {
        Spliterator<Node> spliterator =
            Spliterators.spliterator(iterator(), nodeList.getLength(), 0);
        return StreamSupport.stream(spliterator, false);
    }
}

Then use it like this: new IteratableNodeList(doc.getElementsByTagName(elementType)). stream().filter(...)

Or: new IteratableNodeList(doc.getElementsByTagName(elementType)).forEach(...)

Answer 3

The workaround for this problem is straight-forward, and, thankfully you have to implements it only once.

import java.util.*;
import org.w3c.dom.*;

public final class XmlUtil {
  private XmlUtil(){}

  public static List<Node> asList(NodeList n) {
    return n.getLength()==0?
      Collections.<Node>emptyList(): new NodeListWrapper(n);
  }
  static final class NodeListWrapper extends AbstractList<Node>
  implements RandomAccess {
    private final NodeList list;
    NodeListWrapper(NodeList l) {
      list=l;
    }
    public Node get(int index) {
      return list.item(index);
    }
    public int size() {
      return list.getLength();
    }
  }
}

Once you have added this utility class to your project and added a static import for the XmlUtil.asList method to your source code you can use it like this:

for(Node n: asList(dom.getElementsByTagName("year"))) {
  …
}

Answer 4

One can use the Java8 stream to iterate the NodeList.

NodeList filterList = source.getChildNodes();

IntStream.range(0, filterList.getLength()).boxed().map(filterList::item).forEach(node -> {


});