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.utils;
  
  import java.io.IOException;
  import java.lang.reflect.Constructor;
  import java.lang.reflect.Modifier;
  import java.util.Collection;
  import java.util.Set;
  import java.util.stream.Collectors;
  
  import com.google.common.reflect.ClassPath;
  import com.puppycrawl.tools.checkstyle.AbstractAutomaticBean;
  import com.puppycrawl.tools.checkstyle.TreeWalkerFilter;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck;
  import com.puppycrawl.tools.checkstyle.api.AuditListener;
  import com.puppycrawl.tools.checkstyle.api.BeforeExecutionFileFilter;
  import com.puppycrawl.tools.checkstyle.api.Filter;
  import com.puppycrawl.tools.checkstyle.api.RootModule;
  
  /**
   * Contains utility methods for module reflection.
   */
  public final class ModuleReflectionUtil {
  
      /** Prevent instantiation. */
      private ModuleReflectionUtil() {
      }
  
      /**
       * Gets checkstyle's modules classes (directly, not recursively) in the given packages.
       *
       * @param packages the collection of package names to use
       * @param loader the class loader used to load Checkstyle package names
       * @return the set of checkstyle's module classes
       * @throws IOException if the attempt to read class path resources failed
       * @see #isCheckstyleModule(Class)
       */
      public static Set<Class<?>> getCheckstyleModules(
              Collection<String> packages, ClassLoader loader) throws IOException {
          final ClassPath classPath = ClassPath.from(loader);
          return packages.stream()
                  .flatMap(pkg -> classPath.getTopLevelClasses(pkg).stream())
                  .map(ClassPath.ClassInfo::load)
                  .filter(ModuleReflectionUtil::isCheckstyleModule)
                  .collect(Collectors.toSet());
      }
  
      /**
       * Checks whether a class may be considered as a checkstyle module.
       * Checkstyle's modules are classes which extend 'AutomaticBean', is
       * non-abstract, and has a default constructor.
       *
       * @param clazz class to check.
       * @return true if a class may be considered a valid production class.
       */
      public static boolean isCheckstyleModule(Class<?> clazz) {
          return AbstractAutomaticBean.class.isAssignableFrom(clazz)
                  && !Modifier.isAbstract(clazz.getModifiers())
                  && hasDefaultConstructor(clazz)
                  && isNotXpathFileGenerator(clazz);
      }
  
      /**
       * Checks if the class has a default constructor.
       *
       * @param clazz class to check
       * @return true if the class has a default constructor.
       */
      private static boolean hasDefaultConstructor(Class<?> clazz) {
          boolean result = false;
          for (Constructor<?> constructor : clazz.getDeclaredConstructors()) {
              if (constructor.getParameterCount() == 0) {
                  result = true;
                  break;
              }
          }
          return result;
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle check
       * which has TreeWalker as a parent.
       * Checkstyle's checks are classes which implement 'AbstractCheck' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle check.
       */
      public static boolean isCheckstyleTreeWalkerCheck(Class<?> clazz) {
          return AbstractCheck.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle file set.
       * Checkstyle's file sets are classes which implement 'AbstractFileSetCheck' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle file set.
       */
      public static boolean isFileSetModule(Class<?> clazz) {
          return AbstractFileSetCheck.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle filter.
       * Checkstyle's filters are classes which implement 'Filter' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle filter.
       */
      public static boolean isFilterModule(Class<?> clazz) {
          return Filter.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle file filter.
       * Checkstyle's file filters are classes which implement 'BeforeExecutionFileFilter' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle file filter.
       */
      public static boolean isFileFilterModule(Class<?> clazz) {
          return BeforeExecutionFileFilter.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle audit listener module.
       * Checkstyle's audit listener modules are classes which implement 'AuditListener' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle audit listener module.
       */
      public static boolean isAuditListener(Class<?> clazz) {
          return AuditListener.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle root module.
       * Checkstyle's root modules are classes which implement 'RootModule' interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle root module.
       */
      public static boolean isRootModule(Class<?> clazz) {
          return RootModule.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class may be considered as the checkstyle {@code TreeWalker} filter.
       * Checkstyle's {@code TreeWalker} filters are classes which implement 'TreeWalkerFilter'
       * interface.
       *
       * @param clazz class to check.
       * @return true if a class may be considered as the checkstyle {@code TreeWalker} filter.
       */
      public static boolean isTreeWalkerFilterModule(Class<?> clazz) {
          return TreeWalkerFilter.class.isAssignableFrom(clazz);
      }
  
      /**
       * Checks whether a class is {@code XpathFileGeneratorAstFilter} or
       * {@code XpathFileGeneratorAuditListener}.
       * See issue <a href="https://github.com/checkstyle/checkstyle/issues/102">#102</a>
       *
       * @param clazz class to check.
       * @return true if a class name starts with `XpathFileGenerator`.
       */
      private static boolean isNotXpathFileGenerator(Class<?> clazz) {
          return !clazz.getSimpleName().startsWith("XpathFileGenerator");
      }
  }
  