Java: How do I ignore certain elements when comparing XML?

Question

I have an XML message like so:

<root>
  <elementA>something</elementA>
  <elementB>something else</elementB>
  <elementC>yet another thing</elementC>
</root>

I want to compare a message of this type produced by a method under test to an expected message, but I don't care about elementA. So, I'd like the above message to be considered equal to:

<root>
  <elementA>something different</elementA>
  <elementB>something else</elementB>
  <elementC>yet another thing</elementC>
</root>

I'm using the latest version of XMLUnit.

I'm imagining that the answer involves creating a custom DifferenceListener; I just don't want to reinvent the wheel if there's something ready to use out there.

Suggestions that use a library other than XMLUnit are welcome.

Answer 1

I would use XSLT and the identity transform to filter out elements I want to ignore, and compare the results.

See XSL: how to copy a tree, but removing some nodes ? earlier on SO.

Answer 2

I wound up implementing a DifferenceListener that takes a list of node names (with namespaces) to ignore textual differences for:

public class IgnoreNamedElementsDifferenceListener implements DifferenceListener {
    private Set<String> blackList = new HashSet<String>();

    public IgnoreNamedElementsDifferenceListener(String ... elementNames) {
        for (String name : elementNames) {
            blackList.add(name);
        }
    }

    public int differenceFound(Difference difference) {
        if (difference.getId() == DifferenceConstants.TEXT_VALUE_ID) {
            if (blackList.contains(difference.getControlNodeDetail().getNode().getParentNode().getNodeName())) {
                return DifferenceListener.RETURN_IGNORE_DIFFERENCE_NODES_IDENTICAL;
            }
        }

        return DifferenceListener.RETURN_ACCEPT_DIFFERENCE;
    }

    public void skippedComparison(Node node, Node node1) {

    }
}