001 /* 002 * Copyright 2006 Stephen J. McConnell. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or 013 * implied. 014 * 015 * See the License for the specific language governing permissions and 016 * limitations under the License. 017 */ 018 019 package net.dpml.lang; 020 021 import java.util.ServiceLoader; 022 023 /** 024 * Default service registry implementation that resolves services via 025 * services resolvable using <tt>java.util.ServiceLoader</tt>. 026 * 027 * @author <a href="http://www.dpml.net">Digital Product Management Library</a> 028 * @version 2.1.0 029 */ 030 public class StandardServiceRegistry implements ServiceRegistry 031 { 032 private final ServiceRegistry m_parent; 033 034 /** 035 * Creation of a new service registry with no parent. 036 */ 037 public StandardServiceRegistry() 038 { 039 this( null ); 040 } 041 042 /** 043 * Creation of a new service registry with fallback delegation to 044 * a parent registry. 045 * 046 * @param parent an optional parent registry 047 */ 048 public StandardServiceRegistry( ServiceRegistry parent ) 049 { 050 m_parent = parent; 051 } 052 053 /** 054 * Matches a service in the registry with the supplied type. If no 055 * match is found and a parent registry has been delclared, the lookup 056 * request is passed onto the parent registry, otherwise null is 057 * returned. 058 * @param type the service type to locate 059 * @return an instance of the type or null if unresolvable 060 */ 061 public <T>T lookup( Class<T> type ) 062 { 063 ServiceLoader<T> loaders = ServiceLoader.load( type ); 064 for( T service : loaders ) 065 { 066 return service; // the first available 067 } 068 if( null != m_parent ) 069 { 070 return m_parent.lookup( type ); 071 } 072 return null; 073 } 074 } 075