Java : how to know when a XML Document has been modified

Question

Is there some clean method to know when some content of a DOM Document has been modified, without having to recurse into its nodes and hashing tons of data ?

I would avoid to generate the full XML String (see @AdriaanKoster' response)

Using a listener or whatever "clever", as @mthmulders pointed it out, seems to be the right way.

I found an interesting SO post here , maybe is it THE answer ?

Any tip ?

Thanks

Answer 1

You could check whether your Document also is an instance of EventTarget . If so, you can use the addEventListener method to handle any events. For example, if the event being handled is a MutationEvent , you might get information about the modification to the document.

Answer 2

I did this once by serializing the Document to String and taking its hashcode. Not an extremely expensive operation I think. It goes something like this:

private int calculateHashCode(org.w3c.dom.Document document) {
    try { 
        DOMSource source = new DOMSource(document);
        StringWriter writer = new StringWriter();
        StreamResult result = new StreamResult(stringWriter);
        TransformerFactory factory = TransformerFactory.newInstance();
        Transformer transformer = factory.newTransformer();
        transformer.setOutputProperty("indent","no");
        transformer.transform(domSource, result);        
        return stringWriter.toString().hashCode();
    }
    catch(TransformerException e) {
        return -1;
    }
}

I am returning -1 in case of an exception because I don't want to burden the calling code with exception handling whilst determining the hashCode. It means that changes in documents which cannot be transformed successfully will not be detected correctly.