Remove empty nodes from a XML recursively

Question

I want to delete the empty nodes from an XML element. This xml is generated from a vendor and i dont have control on xml generation. But since the XML has few empty nodes i need to delete those empty nodes recursively.

This xml is got from OMElement and i get an Element from this object using [XMLUtils][1] Sample XML

<A>
  <B>
    <C>
      <C1>
        <C11>something</C11>
        <C12>something</C12>
      </C1>
    </C>
    <D>
      <D1>
        <D11>
          <D111 operation="create">
            <Node>something else</Node>
          </D11>
        </D11>
      </D1>
      <D2>
        <D21>

        </D21>
      </D2>
    </D>
  </B>
</A> 

Since D21 is an empty node i want to delete D21 and since now D2 is an empty node i want to delete D2 but since D has D1 i dont want to delete D.

Similarly it is possible that i can get

<A>
  <B>
    <C>

    </C>
  </B>
</A>

Now since C is empty i want to delete C and then B and then eventually node A. I am trying to do this using removeChild() method in Node

But so far i am unable to remove them recursively. Any suggestions to remove them recursively?

I am recursively trying to get node and node length. But node length is of no help

if(childNode.getChildNodes().getLength() == 0 ){
       childNode.getParentNode().removeChild(childNode);

               }

Regards
Dheeraj Joshi

Answer 1

I don't have enough rep to comment on @Adam's solution, but I was having an issue where after a node removal, the last sibling of that node was moved to index zero, causing it to not fully remove empty elements. The fix was to use a list to hold all of the nodes we want to recursively call for removal.

Also, there was a bug that removed empty elements that had attributes.

Solution to both issues:

public static void removeEmptyNodes(Node node) {

    NodeList list = node.getChildNodes();
    List<Node> nodesToRecursivelyCall = new LinkedList();

    for (int i = 0; i < list.getLength(); i++) {
        nodesToRecursivelyCall.add(list.item(i));
    }

    for(Node tempNode : nodesToRecursivelyCall) {
        removeEmptyNodes(tempNode);
    }

    boolean emptyElement = node.getNodeType() == Node.ELEMENT_NODE 
          && node.getChildNodes().getLength() == 0;
    boolean emptyText = node.getNodeType() == Node.TEXT_NODE 
          && node.getNodeValue().trim().isEmpty();

    if (emptyElement || emptyText) {
        if(!node.hasAttributes()) {
            node.getParentNode().removeChild(node);
        }
    }

}

Answer 2

This works, just create a recursive function that "goes deep" first, then removes empty nodes on the way "back up the tree", this will have the effect of removing both D21 and D2.

public static void main(String[] args) throws Exception {

    DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
    String input = "<A><B><C><C1><C11>something</C11><C12>something</C12></C1></C><D><D1><D11><D111 operation=\"create\"><Node>something else</Node></D111></D11></D1><D2><D21></D21></D2></D></B></A>";

    Document document = builder.parse(new InputSource(new StringReader(
            input)));

    removeNodes(document);

    Transformer transformer = TransformerFactory.newInstance()
            .newTransformer();
    transformer.setOutputProperty(OutputKeys.INDENT, "yes");
    StreamResult result = new StreamResult(new StringWriter());
    transformer.transform(new DOMSource(document), result);
    System.out.println(result.getWriter().toString());
}

public static void removeNodes(Node node) {
    NodeList list = node.getChildNodes();
    for (int i = 0; i < list.getLength(); i++) {
        removeNodes(list.item(i));
    }
    boolean emptyElement = node.getNodeType() == Node.ELEMENT_NODE
            && node.getChildNodes().getLength() == 0;
    boolean emptyText = node.getNodeType() == Node.TEXT_NODE
            && node.getNodeValue().trim().isEmpty();
    if (emptyElement || emptyText) {
        node.getParentNode().removeChild(node);
    }
}

Output

<A>
<B>
<C>
<C1>
<C11>something</C11>
<C12>something</C12>
</C1>
</C>
<D>
<D1>
<D11>
<D111 operation="create">
<Node>something else</Node>
</D111>
</D11>
</D1>
</D>
</B>
</A>