| /* |
| * Copyright (c) 2007, Rickard Öberg. All Rights Reserved. |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| * |
| */ |
| |
| package org.qi4j.runtime.injection.provider; |
| |
| import org.qi4j.runtime.injection.InjectionContext; |
| import org.qi4j.runtime.injection.InjectionProvider; |
| |
| /** |
| * If a dependency resolution should be a singleton, wrap it with this |
| * to provide a single instance "cache". |
| */ |
| public final class CachingInjectionProviderDecorator |
| implements InjectionProvider |
| { |
| private final InjectionProvider decoratedProvider; |
| private volatile Object singletonInstance; |
| |
| public CachingInjectionProviderDecorator( InjectionProvider injectionProvider ) |
| { |
| this.decoratedProvider = injectionProvider; |
| } |
| |
| public InjectionProvider decoratedProvider() |
| { |
| return decoratedProvider; |
| } |
| |
| @Override |
| public Object provideInjection( InjectionContext context ) |
| throws InjectionProviderException |
| { |
| if( singletonInstance == null ) |
| { |
| synchronized( this ) |
| { |
| if( singletonInstance == null ) |
| { |
| singletonInstance = decoratedProvider.provideInjection( context ); |
| } |
| } |
| } |
| |
| return singletonInstance; |
| } |
| } |