MediaPackageElementBuilderFactory.java

/**
 * Licensed to The Apereo Foundation under one or more contributor license
 * agreements. See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 *
 * The Apereo Foundation licenses this file to you under the Educational
 * Community 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://opensource.org/licenses/ecl2.txt
 *
 * 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.opencastproject.mediapackage;

import org.opencastproject.util.ConfigurationException;

/**
 * Factory to retreive instances of a media package element builder. Use the static method {@link #newInstance()} to
 * obtain a reference to a concrete implementation of a <code>MediaPackageElementBuilderFactory</code>. This instance
 * can then be used to create or load media package elements.
 * <p>
 * The factory can be configured by specifying the concrete implementation class through the system property
 * <code>org.opencastproject.mediapackage.elementbuilder</code>.
 * </p>
 */
public final class MediaPackageElementBuilderFactory {

  /** The implementation class name */
  private static String builderClassName = "org.opencastproject.mediapackage.MediaPackageElementBuilderImpl";

  /** The singleton instance of this factory */
  private static final MediaPackageElementBuilderFactory factory = new MediaPackageElementBuilderFactory();

  /** The default builder implementation */
  private MediaPackageElementBuilder builder = null;

  /**
   * Returns an instance of a MediaPackageElementBuilderFactory.
   *
   * @return the media package element builder factory
   * @throws ConfigurationException
   *           if the factory cannot be instantiated
   */
  public static MediaPackageElementBuilderFactory newInstance() throws ConfigurationException {
    return factory;
  }

  /**
   * Factory method that returns an instance of a media package element builder.
   * <p>
   * It uses the following ordered lookup procedure to determine which implementation of the
   * {@link MediaPackageElementBuilder} interface to use:
   * <ul>
   * <li>Implementation specified using the <code>org.opencastproject.mediapackage.elementbuilder</code> system property
   * </li>
   * <li>Platform default implementation</li>
   * </ul>
   *
   * @return the media package element builder
   * @throws ConfigurationException
   *           If the builder cannot be instantiated
   */
  public MediaPackageElementBuilder newElementBuilder() throws ConfigurationException {
    if (builder == null) {
      try {
        Class<?> builderClass = Class.forName(builderClassName, true,
                MediaPackageElementBuilderFactory.class.getClassLoader());
        builder = (MediaPackageElementBuilder) builderClass.newInstance();
      } catch (ClassNotFoundException e) {
        throw new ConfigurationException("Class not found while creating element builder: " + e.getMessage(), e);
      } catch (InstantiationException e) {
        throw new ConfigurationException("Instantiation exception while creating element builder: " + e.getMessage(), e);
      } catch (IllegalAccessException e) {
        throw new ConfigurationException("Access exception while creating element builder: " + e.getMessage(), e);
      } catch (Exception e) {
        throw new ConfigurationException("Exception while creating element builder: " + e.getMessage(), e);
      }
    }
    return builder;
  }

}