XmlUtils.java

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package builder.graphbuilder;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.function.Predicate;

/**
 * Provides utility methods for parsing and processing XML data.
 */
class XmlUtils {
  private XmlUtils() {
  }


  /**
   * Parses the content of the given resource as an XML document.
   */
  static Document parse(URL resource) {
    try {
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
      DocumentBuilder db = dbf.newDocumentBuilder();
      try (InputStream is = resource.openStream()) {
        Document document = db.parse(is);
        return document;
      }
    } catch (Exception ex) {
      throw new RuntimeException(ex);
    }
  }

  /**
   * Returns the direct child elements with the given name.
   */
  static Iterable<Element> getChildrenByTagName(Element parent, String name) {
    return new DescendantsIterable(parent, name, true, element -> true);
  }

  /**
   * Returns all descendant elements with the given name.
   */
  static Iterable<Element> getDescendantsByTagName(Element parent, String name) {
    return new DescendantsIterable(parent, name, false, element -> true);
  }

  /**
   * Returns all descendant elements with the given name.
   */
  static Iterable<Element> getDescendantsByTagName(Element parent, String name, Predicate<Element> predicate) {
    return new DescendantsIterable(parent, name, false, predicate);
  }


  /**
   * Adapts low-level element traversal idoms to {@link Iterable}.
   */
  private static final class DescendantsIterable implements Iterable<Element> {
    final Element parent;
    final String name;
    final boolean childrenOnly;
    final Predicate<Element> predicate;

    DescendantsIterable(
      Element parent, String name, boolean childrenOnly, Predicate<Element> predicate
    ) {
      this.parent = parent;
      this.name = name;
      this.childrenOnly = childrenOnly;
      this.predicate = predicate;
    }

    @Override
    public Iterator<Element> iterator() {
      if (childrenOnly) {
        ArrayList<Element> children = new ArrayList<>();
        for (Node child = parent.getFirstChild(); child != null; child = child.getNextSibling()) {
          if (Node.ELEMENT_NODE == child.getNodeType() &&
              name.equals(child.getNodeName()) &&
              predicate.test((Element) child)) {
            children.add((Element) child);
          }
        }
        return children.iterator();
      } else {
        ArrayList<Element> elements = new ArrayList<>();
        NodeList elementsByTagName = parent.getElementsByTagName(name);
        for (int i = 0; i < elementsByTagName.getLength(); i++) {
          Element element = (Element) elementsByTagName.item(i);
          if (predicate.test(element)) {
            elements.add(element);
          }
        }
        return elements.iterator();
      }
    }
  }
}