org.flyte.jflyte.utils.ChildFirstClassLoader Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of jflyte-utils Show documentation
Primarily used by jflyte, but can also be used to extend or build a jflyte alternative
There is a newer version: 0.4.60
/*
 * Copyright 2020-2023 Flyte Authors.
 *
 * Licensed 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 org.flyte.jflyte.utils;

import com.google.errorprone.annotations.Var;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/**
 * {@link URLClassLoader} that loads classes into child class loader, instead of parent.
 *
 * This way we can keep parent class loader clean from unnecessary classes, and load conflicting
 * classes into multiple children class loaders.
 *
 * All "api" classes must be loaded in parent class loader, because they act as common interface
 * between the code in parent class loader, and the code loaded in child class loaders, and we pass
 * instances of these classes around.
 */
public class ChildFirstClassLoader extends URLClassLoader {

  // we have to load these classes in parent class loader
  // it's base shared between all plugins and user code
  private static final Set PARENT_FIRST_PACKAGE_PREFIXES =
      Set.of("org.flyte.api.v1.", "org.flyte.jflyte.api.");

  private static final Set CHILD_ONLY_PREFIXES =
      Set.of("org.slf4j.impl.", "org/slf4j/impl/", "META-INF/services/");

  @SuppressWarnings("JdkObsolete")
  private static class CustomEnumeration implements Enumeration {

    private final Iterator iter;

    CustomEnumeration(Iterator iter) {
      this.iter = iter;
    }

    @Override
    public boolean hasMoreElements() {
      return iter.hasNext();
    }

    @Override
    public URL nextElement() {
      return iter.next();
    }
  }

  public ChildFirstClassLoader(URL[] urls) {
    super(urls, ChildFirstClassLoader.class.getClassLoader());
  }

  @Override
  protected synchronized Class loadClass(String name, boolean resolve)
      throws ClassNotFoundException {
    @Var Class cls = findLoadedClass(name);

    if (cls == null) {
      if (parentFirst(name)) {
        return super.loadClass(name, resolve);
      }

      try {
        cls = findClass(name);
      } catch (ClassNotFoundException e) {
        if (childOnly(name)) {
          throw e;
        }
        cls = getParent().loadClass(name);
      }
    }

    if (resolve) {
      resolveClass(cls);
    }

    return cls;
  }

  @Override
  public URL getResource(String name) {
    URL resource = findResource(name);

    if (resource != null) {
      return resource;
    }

    return childOnly(name) ? null : getParent().getResource(name);
  }

  @Override
  public Enumeration getResources(String name) throws IOException {
    Enumeration childResources = findResources(name);

    List allResources = new ArrayList<>();

    while (childResources.hasMoreElements()) {
      allResources.add(childResources.nextElement());
    }

    if (!childOnly(name)) {
      Enumeration parentResources = getParent().getResources(name);

      while (parentResources.hasMoreElements()) {
        allResources.add(parentResources.nextElement());
      }
    }

    return new CustomEnumeration(allResources.iterator());
  }

  private static boolean parentFirst(String name) {
    return PARENT_FIRST_PACKAGE_PREFIXES.stream().anyMatch(name::startsWith);
  }

  private static boolean childOnly(String name) {
    return CHILD_ONLY_PREFIXES.stream().anyMatch(name::startsWith);
  }
}