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.checks.javadoc;
  
  import java.io.File;
  import java.io.IOException;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  import com.puppycrawl.tools.checkstyle.GlobalStatefulCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck;
  import com.puppycrawl.tools.checkstyle.api.CheckstyleException;
  import com.puppycrawl.tools.checkstyle.api.FileText;
  
  /**
   * <p>
   * Checks that each Java package has a Javadoc file used for commenting.
   * By default, it only allows a {@code package-info.java} file,
   * but can be configured to allow a {@code package.html} file.
   * </p>
   * <p>
   * A violation will be reported if both files exist as this is not allowed by the Javadoc tool.
   * </p>
   * <ul>
   * <li>
   * Property {@code allowLegacy} - Allow legacy {@code package.html} file to be used.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * <li>
   * Property {@code fileExtensions} - Specify the file type extension of files to process.
   * Type is {@code java.lang.String[]}.
   * Default value is {@code .java}.
   * </li>
   * </ul>
   * <p>
   * To configure the check:
   * </p>
   * <pre>
   * &lt;module name="JavadocPackage"/&gt;
   * </pre>
   * <p>
   * To configure the check to use legacy {@code package.html} file
   * when {@code package-info.java} file is absent:
   * </p>
   * <pre>
   * &lt;module name="JavadocPackage"&gt;
   *   &lt;property name="allowLegacy" value="true"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.Checker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code javadoc.legacyPackageHtml}
   * </li>
   * <li>
   * {@code javadoc.packageInfo}
   * </li>
   * </ul>
   *
   * @since 5.0
   */
  @GlobalStatefulCheck
  public class JavadocPackageCheck extends AbstractFileSetCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_LEGACY_PACKAGE_HTML = "javadoc.legacyPackageHtml";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_PACKAGE_INFO = "javadoc.packageInfo";
  
      /** The directories checked. */
      private final Set<File> directoriesChecked = ConcurrentHashMap.newKeySet();
  
      /** Allow legacy {@code package.html} file to be used. */
      private boolean allowLegacy;
  
      /**
       * Creates a new instance.
       */
      public JavadocPackageCheck() {
          // java, not html!
          // The rule is: Every JAVA file should have a package.html sibling
          setFileExtensions("java");
      }
  
      @Override
      protected void processFiltered(File file, FileText fileText) throws CheckstyleException {
          // Check if already processed directory
          final File dir;
          try {
              dir = file.getCanonicalFile().getParentFile();
          }
          catch (IOException ex) {
              throw new CheckstyleException(
                      "Exception while getting canonical path to file " + file.getPath(), ex);
          }
          final boolean isDirChecked = !directoriesChecked.add(dir);
          if (!isDirChecked) {
              // Check for the preferred file.
              final File packageInfo = new File(dir, "package-info.java");
              final File packageHtml = new File(dir, "package.html");
  
              if (packageInfo.exists()) {
                  if (packageHtml.exists()) {
                      log(1, MSG_LEGACY_PACKAGE_HTML);
                  }
              }
              else if (!allowLegacy || !packageHtml.exists()) {
                  log(1, MSG_PACKAGE_INFO);
              }
          }
      }
  
      /**
       * Setter to allow legacy {@code package.html} file to be used.
       *
       * @param allowLegacy whether to allow support.
       */
      public void setAllowLegacy(boolean allowLegacy) {
          this.allowLegacy = allowLegacy;
      }
  
  }
  