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