001    // Copyright 2009, 2011 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    // http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.internal.services;
016    
017    import org.apache.tapestry5.ioc.ObjectCreator;
018    
019    /**
020     * An {@link org.apache.tapestry5.ioc.ObjectCreator} that delegates to another
021     * {@link org.apache.tapestry5.ioc.ObjectCreator} and caches the result.
022     */
023    public class CachingObjectCreator<T> implements ObjectCreator<T>
024    {
025        private boolean cached;
026    
027        private T cachedValue;
028    
029        private ObjectCreator<T> delegate;
030    
031        public CachingObjectCreator(ObjectCreator<T> delegate)
032        {
033            this.delegate = delegate;
034        }
035    
036        public synchronized T createObject()
037        {
038            if (!cached)
039            {
040                cachedValue = delegate.createObject();
041                cached = true;
042                delegate = null;
043            }
044    
045            return cachedValue;
046        }
047    }