Question

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How to canonicalize WSDL files in Java?

I need to reorder some XML nodes using Java. Actually, I need to canonicalize a WSDL file, but some hand-made reordering should do as well.

I know, I can use org.w3c.dom.Document and iterate through all its children, etc., but it’s quite tedious (the NodeList is not even Iterable) and I wonder if there’s something usable.

Answer 1

I’d do it with dom4j. A dom4j Element provides a live List view of its sub-elements, which you can sort. And with a Visitor you can modify an entire document:

Document document = DocumentHelper.parseText(someXml);
final Comparator<Element> comparator = new Comparator<Element>() {
    public int compare(Element o1, Element o2) {
        return o1.getName().compareTo(o2.getName());
    }
};
Visitor visitor = new VisitorSupport() {
    @Override
    public void visit(Element node) {
        @SuppressWarnings("unchecked") // dom4j doesn't know generics yet
        List<Element> elements = node.elements();
        Collections.sort(elements, comparator);
        super.visit(node);
    }
};
document.accept(visitor);
// now write the document back to a file

It doesn’t get much easier than this.

---

Update: After trying to use my own solution much later, I realized that it doesn’t work that way. The list returned by Element.elements() doesn’t like Collections.sort(), so you will have to use the List returned by Element.content(). Unfortunately this means that your comparator will have to deal with Node, rather than Element, which will get very messy if you have mixed content.