1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package org.apache.commons.proxy.provider; 19 20 import org.apache.commons.proxy.ObjectProvider; 21 22 /** 23 * Wraps another object provider, making sure to only call it once, returning the value returned from the wrapped 24 * provider on all subsequent invocations. 25 * 26 * @author James Carman 27 * @since 1.0 28 */ 29 public class SingletonProvider extends ProviderDecorator 30 { 31 //---------------------------------------------------------------------------------------------------------------------- 32 // Fields 33 //---------------------------------------------------------------------------------------------------------------------- 34 35 private Object instance; 36 37 //---------------------------------------------------------------------------------------------------------------------- 38 // Constructors 39 //---------------------------------------------------------------------------------------------------------------------- 40 41 public SingletonProvider( ObjectProvider inner ) 42 { 43 super( inner ); 44 } 45 46 //---------------------------------------------------------------------------------------------------------------------- 47 // ObjectProvider Implementation 48 //---------------------------------------------------------------------------------------------------------------------- 49 50 public Object getObject() 51 { 52 synchronized( this ) 53 { 54 if( instance == null ) 55 { 56 instance = super.getObject(); 57 inner = null; // Garbage collection 58 } 59 } 60 return instance; 61 } 62 } 63