Modifying XPath 2.0 result trees using Saxon

Question

I would like to

add/remove/update elements/attributes/values to the "subTree"
be able to save the updated "targetDoc" back to the "target" file location.
determine which tree model would be best for this xpath + tree modification procedure.

I thought I should somehow be able to get a MutableNodeInfo object, but I don't know how to do this. I tried using the processor.setConfigurationProperty(FeatureKeys.TREE_MODEL, Builder.LINKED_TREE); but this still gives me an underlying node of TinyElementImpl. I require xpath 2.0 to avoid having to enter default namespaces, which is why I am using saxon s9api instead of Java's default DOM model. I would also like to avoid using xslt/xquery if possible because these tree modifications are being done dynamically, making xslt/xquery more complicated in my situation.

public static void main(String[] args) {

    // XML File namesspace URIs
    Hashtable<String, String> namespaceURIs = new Hashtable<>();
    namespaceURIs.put("def", "http://www.cdisc.org/ns/def/v2.0");
    namespaceURIs.put("xmlns", "http://www.cdisc.org/ns/odm/v1.3");
    namespaceURIs.put("xsi", "http://www.w3.org/2001/XMLSchema-instance");
    namespaceURIs.put("xlink", "http://www.w3.org/1999/xlink");
    namespaceURIs.put("", "http://www.cdisc.org/ns/odm/v1.3");
    // The source/target xml document
    String target = "Path to file.xml";
    // An xpath string
    String xpath = "/ODM/Study/MetaDataVersion/ItemGroupDef[@OID/string()='IG.TA']";

    Processor processor = new Processor(true);
    // I thought this tells the processor to use something other than
    // TinyTree
    processor.setConfigurationProperty(FeatureKeys.TREE_MODEL,
            Builder.LINKED_TREE);
    DocumentBuilder builder = processor.newDocumentBuilder();
    XPathCompiler xpathCompiler = processor.newXPathCompiler();
    for (Entry<String, String> entry : namespaceURIs.entrySet()) {
        xpathCompiler.declareNamespace(entry.getKey(), entry.getValue());
    }
    try {
        XdmNode targetDoc = builder.build(Paths.get(target).toFile());
        XPathSelector selector = xpathCompiler.compile(xpath).load();
        selector.setContextItem(targetDoc);
        XdmNode subTree = (XdmNode) selector.evaluateSingle();
        // The following prints: class
        // net.sf.saxon.tree.tiny.TinyElementImpl
        System.out.println(subTree.getUnderlyingNode().getClass());

        /*
         * Here, is where I would like to modify subtree and save modified doc
         */

    } catch (SaxonApiException e) {
        e.printStackTrace();
    }

}

Martin Honnen Martin Honnen · Accepted Answer · 2015-03-05T10:59:09

I think you can supply a DOM node to Saxon and run XPath against it but it that case you don't use the document builder for Saxon's native trees, you build a DOM using the javax.xml.parsers.DocumentBuilder and once you have a W3C DOM node you can supply it to Saxon using the wrap method of a Saxon DocumentBuilder. Here is sample code taken from the file S9APIExamples.java in the Saxon 9.6 resources file:

        // Build the DOM document
        File file = new File("data/books.xml");
        DocumentBuilderFactory dfactory = DocumentBuilderFactory.newInstance();
        dfactory.setNamespaceAware(true);
        javax.xml.parsers.DocumentBuilder docBuilder;
        try {
            docBuilder = dfactory.newDocumentBuilder();
        } catch (ParserConfigurationException e) {
            throw new SaxonApiException(e);
        }
        Document doc;
        try {
            doc = docBuilder.parse(new InputSource(file.toURI().toString()));
        } catch (SAXException e) {
            throw new SaxonApiException(e);
        } catch (IOException e) {
            throw new SaxonApiException(e);
        }
        // Compile the XPath Expression
        Processor proc = new Processor(false);
        DocumentBuilder db = proc.newDocumentBuilder();
        XdmNode xdmDoc = db.wrap(doc);
        XPathCompiler xpath = proc.newXPathCompiler();
        XPathExecutable xx = xpath.compile("//ITEM/TITLE");
        // Run the XPath Expression
        XPathSelector selector = xx.load();
        selector.setContextItem(xdmDoc);
        for (XdmItem item : selector) {
            XdmNode node = (XdmNode) item;
            org.w3c.dom.Node element = (org.w3c.dom.Node) node.getExternalNode();
            System.out.println(element.getTextContent());
        }

There are also samples showing how to use Saxon with JDOM and other mutable tree implementations but I think you need Saxon PE or EE to have direct support for those.

Modifying XPath 2.0 result trees using Saxon

2 Answers