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 /** 022 * Simple service registry implementation that selects the first service 023 * that is type assignable from the list of service instance supplied to 024 * the registry constructor. 025 * 026 * @author <a href="http://www.dpml.net">Digital Product Management Library</a> 027 * @version 2.1.1 028 */ 029 public class SimpleServiceRegistry implements ServiceRegistry 030 { 031 private final ServiceRegistry m_parent; 032 private final Object[] m_args; 033 034 /** 035 * Creation of a new service registry with no parent. 036 * @param args an ordered sequence of thread-safe services 037 */ 038 public SimpleServiceRegistry( Object... args ) 039 { 040 this( null, args ); 041 } 042 043 /** 044 * Creation of a new service registry with no parent. 045 * @param parent an optional fallback registry 046 * @param args an ordered sequence of thread-safe services 047 */ 048 public SimpleServiceRegistry( ServiceRegistry parent, Object... args ) 049 { 050 if( null == args ) 051 { 052 throw new NullPointerException( "args" ); 053 } 054 m_parent = parent; 055 m_args = args; 056 } 057 058 /** 059 * Matches a service in the registry with the supplied type. If no 060 * match is found and a parent registry has been delclared, the lookup 061 * request is passed onto the parent registry, otherwise null is 062 * returned. 063 * @param type the service type 064 * @return an instance of the type or null if the type could not be resolved 065 */ 066 public <T>T lookup( Class<T> type ) 067 { 068 for( Object object : m_args ) 069 { 070 if( null != object ) 071 { 072 Class c = object.getClass(); 073 if( type.isAssignableFrom( c ) ) 074 { 075 return type.cast( object ); 076 } 077 } 078 } 079 if( null != m_parent ) 080 { 081 return m_parent.lookup( type ); 082 } 083 return null; 084 } 085 } 086