    001    /*
    002     * Copyright (c) 2007-2014 Concurrent, 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
    021    package cascading.provider;
    022
    023    import java.net.URL;
    024    import java.util.Collection;
    025    import java.util.Collections;
    026    import java.util.HashMap;
    027    import java.util.Map;
    028    import java.util.Properties;
    029
    030    import 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     */
    038    public 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      }