| /* |
| * 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. |
| * |
| * @since 1.0 |
| */ |
| public class SingletonProvider<T> extends ProviderDecorator<T> |
| { |
| //****************************************************************************************************************** |
| // Fields |
| //****************************************************************************************************************** |
| |
| private static final long serialVersionUID = 1L; |
| |
| private T instance; |
| |
| //****************************************************************************************************************** |
| // Constructors |
| //****************************************************************************************************************** |
| |
| /** |
| * Create a new SingletonProvider instance. |
| * |
| * @param inner |
| */ |
| public SingletonProvider(ObjectProvider<? extends T> inner) |
| { |
| super(inner); |
| } |
| |
| //****************************************************************************************************************** |
| // ObjectProvider Implementation |
| //****************************************************************************************************************** |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public T getObject() |
| { |
| synchronized (this) |
| { |
| if (instance == null) |
| { |
| instance = super.getObject(); |
| // Garbage collection |
| setInner(null); |
| } |
| return instance; |
| } |
| } |
| } |