code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.internal.utils;
  
  import static com.google.common.truth.Truth.assertWithMessage;
  
  import java.io.IOException;
  import java.io.StringReader;
  import java.util.LinkedHashSet;
  import java.util.Set;
  
  import javax.xml.parsers.DocumentBuilder;
  import javax.xml.parsers.DocumentBuilderFactory;
  import javax.xml.parsers.ParserConfigurationException;
  
  import org.w3c.dom.Document;
  import org.w3c.dom.NamedNodeMap;
  import org.w3c.dom.Node;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  
  import com.puppycrawl.tools.checkstyle.XmlLoader;
  
  /**
   * XmlUtil.
   *
   * @noinspection ClassOnlyUsedInOnePackage
   * @noinspectionreason ClassOnlyUsedInOnePackage - class is internal tool, and only used in testing
   */
  public final class XmlUtil {
  
      private XmlUtil() {
      }
  
      public static Document getRawXml(String fileName, String code, String unserializedSource)
              throws ParserConfigurationException {
          Document rawXml = null;
          try {
              final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
              factory.setValidating(false);
              factory.setFeature(
                      XmlLoader.LoadExternalDtdFeatureProvider.EXTERNAL_GENERAL_ENTITIES, false);
              factory.setFeature(
                      XmlLoader.LoadExternalDtdFeatureProvider.LOAD_EXTERNAL_DTD, false);
  
              final DocumentBuilder builder = factory.newDocumentBuilder();
  
              rawXml = builder.parse(new InputSource(new StringReader(code)));
          }
          catch (IOException | SAXException ex) {
              assertWithMessage(fileName + " has invalid xml (" + ex.getMessage() + "): "
                      + unserializedSource).fail();
          }
  
          return rawXml;
      }
  
      public static Set<Node> getChildrenElements(Node node) {
          final Set<Node> result = new LinkedHashSet<>();
  
          for (Node child = node.getFirstChild(); child != null; child = child.getNextSibling()) {
              if (child.getNodeType() != Node.TEXT_NODE) {
                  result.add(child);
              }
          }
  
          return result;
      }
  
      public static Node getFirstChildElement(Node node) {
          Node firstChildElement = null;
          for (Node child = node.getFirstChild(); child != null; child = child.getNextSibling()) {
              if (child.getNodeType() != Node.TEXT_NODE) {
                  firstChildElement = child;
                  break;
              }
          }
  
          return firstChildElement;
      }
  
      /**
       * Returns the {@code Node} that has an id attribute with the given value.
       * The id should be unique within the Xml Document.
       *
       * @param node to retrieve information.
       * @param id the unique {@code id} value for a node.
       * @return the matching node or {@code null} if none matches.
       */
      public static Node findChildElementById(Node node, String id) {
          Node childElement = null;
          for (Node child = node.getFirstChild(); child != null; child = child.getNextSibling()) {
              final NamedNodeMap attributes = child.getAttributes();
              if (attributes != null) {
                  final Node attribute = attributes.getNamedItem("id");
                  if (attribute != null && id.equals(attribute.getNodeValue())) {
                      childElement = child;
                      break;
                  }
              }
          }
  
          return childElement;
      }
  
      public static Set<Node> findChildElementsByTag(Node node, String tag) {
          final Set<Node> result = new LinkedHashSet<>();
  
          for (Node child = node.getFirstChild(); child != null; child = child.getNextSibling()) {
              if (tag.equals(child.getNodeName())) {
                  result.add(child);
              }
              else if (child.hasChildNodes()) {
                  result.addAll(findChildElementsByTag(child, tag));
              }
          }
  
          return result;
      }
  
      /**
       * Returns the value of the "name" attribute for the given node.
       *
       * @param node to retrieve the name
       * @return the value of the attribute "name"
       */
      public static String getNameAttributeOfNode(Node node) {
          return node.getAttributes().getNamedItem("name").getNodeValue();
      }
  
      /**
       * <p>Sanitizes the given string for safe use in XML documents.</p>
       * <ul>
       * <li>Removes all whitespaces at the beginning and at the end of the string;</li>
       * <li>Replaces repeated whitespaces in the middle of the string with a single space;</li>
       * <li>Replaces XML entities with escaped values.</li>
       * </ul>
       *
       * @param rawXml the text to sanitize
       * @return the sanitized text
       */
      public static String sanitizeXml(String rawXml) {
          return rawXml
                  .replaceAll("(^\\s+|\\s+$)", "")
                  .replaceAll("\\s+", " ")
                  .replace("<", "&lt;")
                  .replace(">", "&gt;");
      }
  
  }
  