DomツリーからXPathでノードを選択するクラス。

DomNode.java

/**
 * DomツリーからXPathでノードを選択するクラス。
 */
public class DomNode {

    private static XPathFactory xpathFactory = XPathFactory.newInstance();

    private Optional<Node> node;

    public DomNode(Node node) {
        this.node = Optional.of(node);
    }

    public Optional<Node> get() {
        return node;
    }

    public String name() {
        return node.map(x -> x.getNodeName()).orElse(null);
    }

    public String attr(String name) {
        return node.map(x -> x.getAttributes().getNamedItem(name))
                .map(x -> x.getNodeValue())
                .orElse(null);
    }

    public String text() {
        return node.map(x -> x.getTextContent()).orElse(null);
    }



    public DomNode selectNode(String path) {
        Objects.requireNonNull(path);
        try {
            return new DomNode((Node) xpathFactory.newXPath().compile(path).evaluate(node.get(), XPathConstants.NODE));
        } catch (XPathExpressionException e) {
            throw new RuntimeException(e);
        }
    }

    public List<DomNode> selectNodeSet(String path) {
        Objects.requireNonNull(path);
        try {
            NodeList nodeList = (NodeList) xpathFactory.newXPath().compile(path).evaluate(node.get(), XPathConstants.NODESET);
            List<DomNode> list = new ArrayList<>();
            for (int i = 0; i < nodeList.getLength(); i++) {
                list.add(new DomNode(nodeList.item(i)));
            }
            return list;
        } catch (XPathExpressionException e) {
            throw new RuntimeException(e);
        }
    }

    public Optional<String> selectText(String path) {
        Objects.requireNonNull(path);
        try {
            String text = (String) xpathFactory.newXPath().compile(path).evaluate(node.get(), XPathConstants.STRING);
            return Optional.ofNullable(text);
        } catch (XPathExpressionException e) {
            throw new RuntimeException(e);
        }
    }
}