    001/*
    002 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
    003 *
    004 * Project and contact information: http://www.cascading.org/
    005 *
    006 * This file is part of the Cascading project.
    007 *
    008 * Licensed under the Apache License, Version 2.0 (the "License");
    009 * you may not use this file except in compliance with the License.
    010 * You may obtain a copy of the License at
    011 *
    012 *     http://www.apache.org/licenses/LICENSE-2.0
    013 *
    014 * Unless required by applicable law or agreed to in writing, software
    015 * distributed under the License is distributed on an "AS IS" BASIS,
    016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017 * See the License for the specific language governing permissions and
    018 * limitations under the License.
    019 */
    020
    021package cascading.provider;
    022
    023import java.net.URL;
    024import java.util.Collection;
    025import java.util.Collections;
    026import java.util.HashMap;
    027import java.util.Map;
    028import java.util.Properties;
    029
    030import static cascading.property.PropertyUtil.getStringProperty;
    031
    032/**
    033 * Class ServiceLoader is an implementation of a {@link ProviderLoader} and is used to load
    034 * {@link CascadingService} instances used by internal frameworks.
    035 *
    036 * @see CascadingService
    037 */
    038public class ServiceLoader extends ProviderLoader<CascadingService>
    039  {
    040  private static ServiceLoader serviceLoader;
    041
    042  private Map<String, CascadingService> singletons = new HashMap<String, CascadingService>();
    043
    044  public synchronized static ServiceLoader getInstance( URL libraryURL, String[] exclusions )
    045    {
    046    if( serviceLoader == null )
    047      serviceLoader = new ServiceLoader( libraryURL, exclusions );
    048
    049    return serviceLoader;
    050    }
    051
    052  public synchronized static void releaseSingletonsAndDestroy()
    053    {
    054    if( serviceLoader != null )
    055      serviceLoader.releaseSingletonServices();
    056
    057    serviceLoader = null;
    058    }
    059
    060  ServiceLoader( URL libraryURL, String[] exclusions )
    061    {
    062    super( exclusions, libraryURL );
    063    }
    064
    065  public synchronized CascadingService loadSingletonServiceFrom( Properties defaultProperties, Map<Object, Object> properties, String property )
    066    {
    067    String className = getStringProperty( defaultProperties, properties, property );
    068
    069    if( !singletons.containsKey( className ) )
    070      singletons.put( className, loadServiceFrom( defaultProperties, properties, property ) );
    071
    072    return singletons.get( className );
    073    }
    074
    075  public synchronized Collection<CascadingService> releaseSingletonServices()
    076    {
    077    try
    078      {
    079      return Collections.unmodifiableCollection( singletons.values() );
    080      }
    081    finally
    082      {
    083      singletons.clear();
    084      }
    085    }
    086
    087  public CascadingService loadServiceFrom( Properties defaultProperties, Map<Object, Object> properties, String property )
    088    {
    089    String className = getStringProperty( defaultProperties, properties, property );
    090
    091    CascadingService service = createProvider( className );
    092
    093    if( service != null )
    094      service.setProperties( properties );
    095
    096    return service;
    097    }
    098  }