001/* 002 * Copyright (c) 2007-2015 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 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 }