SCM-Manager/scm-webapp/src/main/java/sonia/scm/plugin/UberClassLoader.java

/*
 * MIT License
 *
 * Copyright (c) 2020-present Cloudogu GmbH and Contributors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
    
package sonia.scm.plugin;

//~--- non-JDK imports --------------------------------------------------------

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Maps;

import java.io.IOException;
import java.lang.ref.WeakReference;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;

//~--- JDK imports ------------------------------------------------------------

/**
 * {@link ClassLoader} which is able to load classes and resources from all
 * plugins.
 *
 * @author Sebastian Sdorra
 */
public final class UberClassLoader extends ClassLoader {

  private final Set<ClassLoader> pluginClassLoaders;
  private final ConcurrentMap<String, WeakReference<Class<?>>> cache = Maps.newConcurrentMap();

  public UberClassLoader(ClassLoader parent, Iterable<InstalledPlugin> plugins) {
    this(parent, collectClassLoaders(plugins));
  }

  private static Set<ClassLoader> collectClassLoaders(Iterable<InstalledPlugin> plugins) {
    ImmutableSet.Builder<ClassLoader> classLoaders = ImmutableSet.builder();
    plugins.forEach(plugin -> classLoaders.add(plugin.getClassLoader()));
    return classLoaders.build();
  }

  @VisibleForTesting
  UberClassLoader(ClassLoader parent, Set<ClassLoader> pluginClassLoaders) {
    super(parent);
    this.pluginClassLoaders = pluginClassLoaders;
  }

  @Override
  protected Class<?> findClass(String name) throws ClassNotFoundException {
    Class<?> clazz = getFromCache(name);

    if (clazz == null) {
      clazz = findClassInPlugins(name);
      cache.put(name, new WeakReference<>(clazz));
    }

    return clazz;
  }

  private Class<?> findClassInPlugins(String name) throws ClassNotFoundException {
    for (ClassLoader pluginClassLoader : pluginClassLoaders) {
      Class<?> clazz = findClass(pluginClassLoader, name);
      if (clazz != null) {
        return clazz;
      }
    }
    throw new ClassNotFoundException("could not find class " + name + " in any of the installed plugins");
  }

  private Class<?> findClass(ClassLoader classLoader, String name) {
    try {
      // load class could be slow, perhaps we should call
      // find class via reflection ???
      return classLoader.loadClass(name);
    } catch (ClassNotFoundException ex) {
      return null;
    }
  }

  @Override
  protected URL findResource(String name) {
    URL url = null;

    for (ClassLoader pluginClassLoader : pluginClassLoaders) {
      url = pluginClassLoader.getResource(name);

      if (url != null) {
        break;
      }
    }

    return url;
  }

  @Override
  @SuppressWarnings("squid:S2112")
  protected Enumeration<URL> findResources(String name) throws IOException {
    Set<URL> urls = new LinkedHashSet<>();

    for (ClassLoader pluginClassLoader : pluginClassLoaders) {
      urls.addAll(Collections.list(pluginClassLoader.getResources(name)));
    }

    return Collections.enumeration(urls);
  }

  private Class<?> getFromCache(String name) {
    Class<?> clazz = null;
    WeakReference<Class<?>> ref = cache.get(name);

    if (ref != null) {
      clazz = ref.get();

      if (clazz == null) {
        cache.remove(name);
      }
    }

    return clazz;
  }

}