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      }