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1   /*
2    * Copyright [2007] [University Corporation for Advanced Internet Development, Inc.]
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.opensaml.xml.util;
18  
19  import org.slf4j.Logger;
20  import org.slf4j.LoggerFactory;
21  
22  /**
23   * An abstract Template design pattern implementation of {@link SingletonFactory}.
24   *
25   * @param <Input> the factory input class type
26   * @param <Output> the factory output class type
27   */
28  public abstract class AbstractSingletonFactory<Input, Output> implements SingletonFactory<Input, Output> {
29      
30      /** Class logger. */
31      private final Logger log = LoggerFactory.getLogger(AbstractSingletonFactory.class);
32      
33      /** {@inheritDoc} */
34      public synchronized Output getInstance(Input input) {
35          Output output = get(input);
36          if (output != null) {
37              log.trace("Input key mapped to a non-null value, returning output");
38              return output;
39          } else {
40              log.trace("Input key mapped to a null value");
41          }
42          
43          log.trace("Creating new output instance and inserting to factory map");
44          output = createNewInstance(input);
45          if (output == null) {
46              log.error("New output instance was not created");
47              return null;
48           }
49          
50          put(input, output);
51          
52          return output;
53      }
54      
55      /**
56       * Get the output instance currently associated with
57       * the input instance.
58       * 
59       * @param input the input instance key
60       * @return the output instance which corresponds to the input instance,
61       *              or null if not present
62       */
63      protected abstract Output get(Input input);
64      
65      /**
66       * Store the input and output instance association.
67       * 
68       * @param input the input instance key
69       * @param output the output instance value
70       */
71      protected abstract void put(Input input, Output output);
72  
73      /**
74       * Create a new instance of the output class based on the input
75       * class instance.
76       * 
77       * @param input the input class instance
78       * @return an output class instance
79       */
80      protected abstract Output createNewInstance(Input input);
81  
82  }