se.idsec.signservice.integration.core.ContentLoaderSingleton Maven / Gradle / Ivy

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/*
 * Copyright 2019-2024 IDsec Solutions AB
 *
 * 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 se.idsec.signservice.integration.core;

import java.io.IOException;

/**
 * A singleton to be used internally for loading resources. By default, the {@link DefaultContentLoader} is used. This
 * can be overridden by installing a customized content loader using {@link #setContentLoader(ContentLoader)}.
 *
 * @author Martin Lindström ([email protected])
 * @author Stefan Santesson ([email protected])
 */
public class ContentLoaderSingleton implements ContentLoader {

  /** The content loader used. */
  private ContentLoader contentLoader;

  /** The singleton instance. */
  private final static ContentLoaderSingleton INSTANCE = new ContentLoaderSingleton();

  /**
   * Gets the singleton instance of the global content loader.
   *
   * @return a ContentLoader
   */
  public static ContentLoader getInstance() {
    return INSTANCE;
  }

  /** {@inheritDoc} */
  @Override
  public byte[] loadContent(final String resource) throws IOException {
    return this.getContentLoader().loadContent(resource);
  }

  /**
   * If the global {@link ContentLoader} should be something else than {@link DefaultContentLoader} this method should
   * be used to assign this.
   *
   * @param loader the content loader to set
   */
  public void setContentLoader(final ContentLoader loader) {
    if (this.contentLoader != null) {
      throw new IllegalArgumentException("Global ContentLoader has already been configured");
    }
    if (loader != null) {
      this.contentLoader = loader;
    }
  }

  /**
   * Gets the {@link ContentLoader} to use. If a specific content loader has not been assigned (using
   * {@link #setContentLoader(ContentLoader)}) an {@link DefaultContentLoader} instance will be used.
   *
   * @return the content loader to use
   */
  private ContentLoader getContentLoader() {
    if (this.contentLoader == null) {
      this.contentLoader = new DefaultContentLoader();
    }
    return this.contentLoader;
  }

  // Hidden constructor
  private ContentLoaderSingleton() {
  }

}