/* | |
* Licensed to the Apache Software Foundation (ASF) under one or more | |
* contributor license agreements. See the NOTICE file distributed with | |
* this work for additional information regarding copyright ownership. | |
* The ASF licenses this file to You 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.apache.commons.proxy2.provider; | |
import org.apache.commons.proxy2.ObjectProvider; | |
/** | |
* Wraps another object provider, making sure to only call it once, returning the value returned from the wrapped | |
* provider on all subsequent invocations. | |
* | |
* @author James Carman | |
* @since 1.0 | |
*/ | |
public class SingletonProvider<T> extends ProviderDecorator<T> | |
{ | |
//********************************************************************************************************************** | |
// Fields | |
//********************************************************************************************************************** | |
private T instance; | |
//********************************************************************************************************************** | |
// Constructors | |
//********************************************************************************************************************** | |
/** | |
* Create a new SingletonProvider instance. | |
* | |
* @param inner | |
*/ | |
public SingletonProvider(ObjectProvider<? extends T> inner) | |
{ | |
super(inner); | |
} | |
//********************************************************************************************************************** | |
// ObjectProvider Implementation | |
//********************************************************************************************************************** | |
/** | |
* {@inheritDoc} | |
*/ | |
public T getObject() | |
{ | |
synchronized (this) | |
{ | |
if (instance == null) | |
{ | |
instance = super.getObject(); | |
// Garbage collection | |
setInner(null); | |
} | |
return instance; | |
} | |
} | |
} |