001// Copyright 2009, 2011, 2012 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 015package org.apache.tapestry5.ioc.internal.services; 016 017import org.apache.tapestry5.ioc.ObjectCreator; 018import org.apache.tapestry5.ioc.internal.util.LockSupport; 019 020/** 021 * An {@link org.apache.tapestry5.ioc.ObjectCreator} that delegates to another 022 * {@link org.apache.tapestry5.ioc.ObjectCreator} and caches the result. 023 */ 024public class CachingObjectCreator<T> extends LockSupport implements ObjectCreator<T> 025{ 026 private boolean cached; 027 028 private T cachedValue; 029 030 private ObjectCreator<T> delegate; 031 032 public CachingObjectCreator(ObjectCreator<T> delegate) 033 { 034 this.delegate = delegate; 035 } 036 037 public T createObject() 038 { 039 try 040 { 041 acquireReadLock(); 042 043 if (!cached) 044 { 045 cacheValueFromDelegate(); 046 } 047 048 return cachedValue; 049 } finally 050 { 051 releaseReadLock(); 052 } 053 } 054 055 private void cacheValueFromDelegate() 056 { 057 try 058 { 059 upgradeReadLockToWriteLock(); 060 061 if (!cached) 062 { 063 cachedValue = delegate.createObject(); 064 cached = true; 065 delegate = null; 066 } 067 } finally 068 { 069 downgradeWriteLockToReadLock(); 070 } 071 } 072}