001/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
002 *
003 * Copyright © 2025 microBean™.
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
006 * the License. You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
011 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
012 * specific language governing permissions and limitations under the License.
013 */
014package org.microbean.proxy;
015
016import java.util.Objects;
017
018import java.util.function.Supplier;
019
020import org.microbean.construct.Domain;
021
022/**
023 * An abstract base class for subclassses that create {@linkplain Proxy proxies}.
024 *
025 * @param <PS> the {@link ProxySpecification} type
026 *
027 * @author <a href="https://about.me/lairdnelson" target="_top">Laird Nelson</a>
028 */
029public abstract sealed class AbstractProxier<PS extends ProxySpecification>
030  permits AbstractReflectiveProxier, AbstractToolkitProxier {
031
032  private final Domain domain;
033
034  /**
035   * Creates a new {@link AbstractProxier} implementation.
036   *
037   * @param domain a {@link Domain}; must not be {@code null}
038   *
039   * @exception NullPointerException if {@code domain} is {@code null}
040   */
041  protected AbstractProxier(final Domain domain) {
042    this.domain = Objects.requireNonNull(domain, "domain");
043  }
044
045  /**
046   * Returns the {@link ClassLoader} for loading classes.
047   *
048   * <p>The default implementation of this method returns the return value of an invocation of the {@link
049   * Thread#getContextClassLoader()} method.</p>
050   *
051   * <p>Overrides of this method must not return {@code null} or undefined behavior may result.</p>
052   *
053   * @return a non-{@code null} {@link ClassLoader}
054   */
055  protected ClassLoader classLoader() {
056    return Thread.currentThread().getContextClassLoader();
057  }
058  
059  /**
060   * Returns the {@link Domain} supplied at construction time.
061   *
062   * @return a non-{@code null} {@link Domain}
063   */
064  protected final Domain domain() {
065    return this.domain;
066  }
067
068  /**
069   * Returns a {@link Proxy} appropriate for the supplied proxy specification and {@link Supplier} of contextual
070   * instances.
071   *
072   * @param <R> the contextual instance type
073   *
074   * @param ps an appropriate proxy specification; must not be {@code null}
075   *
076   * @param instanceSupplier a {@link Supplier} of contextual instances; must not be {@code null}; may or may not create
077   * a new contextual instance each time it is invoked; may or may not be invoked multiple times depending on the
078   * subclass implementation
079   *
080   * @return a non-{@code null} {@link Proxy}
081   *
082   * @exception NullPointerException if any argument is {@code null}
083   */
084  public abstract <R> Proxy<R> proxy(final PS ps, final Supplier<? extends R> instanceSupplier);
085
086}