content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.alibaba.compileflow.engine.core.infrastructure.utils;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URL;
  import java.util.*;
  
  /**
   * A utility class for handling {@link ClassLoader} and resource loading operations.
   * <p>
   * This class provides a consistent and robust way to load classes and resources,
   * gracefully handling different classloader hierarchies (e.g., context classloader,
   * system classloader) to ensure reliability in various deployment environments.
   *
   * @author wuxiang
   * @author yusu
   */
  public class ClassLoaderUtils {
  
      private static final Logger LOGGER = LoggerFactory.getLogger(ClassLoaderUtils.class);
  
      /**
       * Gets the current thread's context classloader.
       *
       * @return The context classloader.
       */
      public static ClassLoader getContextClassLoader() {
          return Thread.currentThread().getContextClassLoader();
      }
  
      /**
       * Loads a class using the current thread's context classloader.
       *
       * @param className The fully qualified name of the class to load.
       * @return The loaded {@link Class} object.
       * @throws ClassNotFoundException if the class cannot be found.
       */
      public static Class loadClass(String className) throws ClassNotFoundException {
          return loadClass(className, getContextClassLoader());
      }
  
      /**
       * Loads a class using the classloader of a referrer class.
       *
       * @param className The fully qualified name of the class to load.
       * @param referrer  A class whose classloader should be used.
       * @return The loaded {@link Class} object.
       * @throws ClassNotFoundException if the class cannot be found.
       */
      public static Class loadClass(String className, Class<?> referrer) throws ClassNotFoundException {
          ClassLoader classLoader = getReferrerClassLoader(referrer);
          return loadClass(className, classLoader);
      }
  
      /**
       * Loads a class using the specified classloader. If the provided classloader is null,
       * it falls back to {@code Class.forName(className)}.
       *
       * @param className   The fully qualified name of the class to load.
       * @param classLoader The classloader to use.
       * @return The loaded {@link Class} object.
       * @throws ClassNotFoundException if the class cannot be found.
       */
      public static Class<?> loadClass(String className, ClassLoader classLoader) throws ClassNotFoundException {
          if (className == null) {
              return null;
          }
  
          if (classLoader == null) {
              return Class.forName(className);
          } else {
              return Class.forName(className, true, classLoader);
          }
      }
  
      /**
       * Gets the classloader from a referrer class, falling back to the system classloader
       * if the referrer's classloader is null (e.g., for bootstrap classes).
       */
      private static ClassLoader getReferrerClassLoader(Class<?> referrer) {
          ClassLoader classLoader = null;
  
          if (referrer != null) {
              classLoader = referrer.getClassLoader();
  
              if (classLoader == null) {
                  classLoader = ClassLoader.getSystemClassLoader();
              }
          }
  
          return classLoader;
      }
  
      /**
       * Finds all resources with the given name, searching through a standard hierarchy
       * of classloaders (context, this class's, and system).
       *
       * @param resourceName The name of the resource to find.
       * @return An array of {@link URL} objects for all found resources.
       */
      public static URL[] getResources(String resourceName) {
          LinkedList<URL> urls = new LinkedList<>();
          boolean found = getResources(urls, resourceName, getContextClassLoader(), false);
  
          if (!found) {
              getResources(urls, resourceName, ClassLoaderUtils.class.getClassLoader(), false);
          }
  
          if (!found) {
              getResources(urls, resourceName, null, true);
          }
  
          return getDistinctURLs(urls);
      }
  
      /**
       * Finds all resources with the given name using a referrer's classloader.
       *
       * @param resourceName The name of the resource to find.
       * @param referrer     A class whose classloader should be used for the search.
       * @return An array of {@link URL} objects for all found resources.
       */
      public static URL[] getResources(String resourceName, Class<?> referrer) {
          ClassLoader classLoader = getReferrerClassLoader(referrer);
          LinkedList<URL> urls = new LinkedList<>();
  
          getResources(urls, resourceName, classLoader, classLoader == null);
  
          return getDistinctURLs(urls);
      }
  
      /**
       * Finds all resources with the given name using a specific classloader.
       *
       * @param resourceName The name of the resource to find.
       * @param classLoader  The classloader to use for the search.
       * @return An array of {@link URL} objects for all found resources.
       */
      public static URL[] getResources(String resourceName, ClassLoader classLoader) {
          List<URL> urls = new LinkedList<>();
  
          getResources(urls, resourceName, classLoader, classLoader == null);
  
          return getDistinctURLs(urls);
      }
  
      private static Enumeration<URL> getResources(String resourceName, ClassLoader classLoader, boolean sysClassLoader) {
          Enumeration<URL> resource = null;
  
          try {
              if (classLoader != null) {
                  resource = classLoader.getResources(resourceName);
              } else if (sysClassLoader) {
                  resource = ClassLoader.getSystemResources(resourceName);
              }
          } catch (IOException e) {
              LOGGER.error("Failed to getResources: errorType={}, message={}",
                      e.getClass().getSimpleName(), e.getMessage(), e);
          }
          return resource;
      }
  
      private static boolean getResources(List<URL> urlSet, String resourceName, ClassLoader classLoader,
                                          boolean sysClassLoader) {
          if (resourceName == null) {
              return false;
          }
  
          Enumeration<URL> resources = getResources(resourceName, classLoader, sysClassLoader);
  
          if ((resources != null) && resources.hasMoreElements()) {
              while (resources.hasMoreElements()) {
                  urlSet.add(resources.nextElement());
              }
  
              return true;
          }
  
          return false;
      }
  
      /**
       * Removes duplicate URLs from a list.
       */
      private static URL[] getDistinctURLs(List<URL> urls) {
          if ((urls == null) || (urls.size() == 0)) {
              return new URL[0];
          }
  
          Set<URL> urlSet = new HashSet<>(urls.size());
  
          for (Iterator<URL> i = urls.iterator(); i.hasNext(); ) {
              URL url = i.next();
  
              if (urlSet.contains(url)) {
                  i.remove();
              } else {
                  urlSet.add(url);
              }
          }
  
          return urls.toArray(new URL[0]);
      }
  
      /**
       * Finds the first resource with the given name using a standard search hierarchy.
       *
       * @param resourceName The name of the resource to find.
       * @return A {@link URL} object, or null if the resource is not found.
       */
      public static URL getResource(String resourceName) {
          if (resourceName == null) {
              return null;
          }
  
          ClassLoader classLoader = getContextClassLoader();
          URL url;
  
          if (classLoader != null) {
              url = classLoader.getResource(resourceName);
  
              if (url != null) {
                  return url;
              }
          }
  
          classLoader = ClassLoaderUtils.class.getClassLoader();
  
          if (classLoader != null) {
              url = classLoader.getResource(resourceName);
  
              if (url != null) {
                  return url;
              }
          }
  
          return ClassLoader.getSystemResource(resourceName);
      }
  
      /**
       * Finds the first resource with the given name using a referrer's classloader.
       *
       * @param resourceName The name of the resource to find.
       * @param referrer     A class whose classloader should be used.
       * @return A {@link URL} object, or null if the resource is not found.
       */
      public static URL getResource(String resourceName, Class<?> referrer) {
          if (resourceName == null) {
              return null;
          }
  
          ClassLoader classLoader = getReferrerClassLoader(referrer);
  
          return (classLoader == null)
                  ? ClassLoaderUtils.class.getClassLoader().getResource(resourceName)
                  : classLoader.getResource(resourceName);
      }
  
      /**
       * Finds the first resource with the given name using a specific classloader.
       *
       * @param resourceName The name of the resource to find.
       * @param classLoader  The classloader to use.
       * @return A {@link URL} object, or null if the resource is not found.
       */
      public static URL getResource(String resourceName, ClassLoader classLoader) {
          if (resourceName == null) {
              return null;
          }
  
          return (classLoader == null)
                  ? ClassLoaderUtils.class.getClassLoader().getResource(resourceName)
                  : classLoader.getResource(resourceName);
      }
  
      /**
       * Opens an {@link InputStream} for a resource found via the standard search hierarchy.
       *
       * @param resourceName The name of the resource.
       * @return An {@link InputStream}, or null if the resource is not found.
       */
      public static InputStream getResourceAsStream(String resourceName) {
          URL url = getResource(resourceName);
  
          try {
              if (url != null) {
                  return url.openStream();
              }
          } catch (IOException e) {
              LOGGER.error("Failed to getResourceAsStream, resourceName is {}", resourceName, e);
          }
  
          return null;
      }
  
      /**
       * Opens an {@link InputStream} for a resource found via a specific classloader.
       *
       * @param resourceName The name of the resource.
       * @param classLoader  The classloader to use.
       * @return An {@link InputStream}, or null if the resource is not found.
       */
      public static InputStream getResourceAsStream(String resourceName, ClassLoader classLoader) {
          URL url = getResource(resourceName, classLoader);
  
          try {
              if (url != null) {
                  return url.openStream();
              }
          } catch (IOException e) {
              LOGGER.error("Failed to getResourceAsStream: resourceName={}, errorType={}, message={}",
                      resourceName, e.getClass().getSimpleName(), e.getMessage(), e);
          }
  
          return null;
      }
  
  }
  