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1   /*
2    * Copyright 2005 The Apache Software Foundation.
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.apache.commons.betwixt.strategy;
18  
19  import org.apache.commons.betwixt.expression.Context;
20  
21  /***
22   * Pluggable strategy for id storage management.
23   * It is possible to use this strategy for innovative
24   * active storage storage strategies as well as passive ones.
25   * For example, it is possible to have some beans map to 
26   * references without ever being fully mapped.
27   * 
28   * @author <a href="mailto:christian@wilde-welt.de">Christian Aust </a>
29   * @since 0.7
30   */
31  public abstract class IdStoringStrategy {
32  
33      /***
34       * Default storage strategy
35       * 
36       * @see DefaultIdStoringStrategy
37       */
38      public static IdStoringStrategy DEFAULT = new DefaultIdStoringStrategy();
39  
40      /***
41       * Retrieves a reference for the given instance.
42       * If a not null value is returned from this method,
43       * then the bean content will not be written.
44       * Use {@link org.apache.commons.betwixt.io.IDGenerator} strategy to vary the values
45       * written for a bean.
46       * 
47       * @param context
48       *            current context, not null
49       * @param bean
50       *            the instance, not null
51       * @return id as String when this bean has already been reference, 
52       * or null to indicate that this bean is not yet reference
53       */
54      public abstract String getReferenceFor(Context context, Object bean);
55  
56      /***
57       * Stores an instance reference for later retrieval.
58       * This method is shared by writing and reading.
59       *  
60       * @param context
61       *            current context, not null
62       * @param bean
63       *            the instance, not null
64       * @param id
65       *            the id to use
66       */
67      public abstract void setReference(Context context, Object bean, String id);
68  
69      /***
70       * Gets an object matching the given reference.
71       * @param context <code>Context</code>, not null
72       * @param id the reference id
73       * @return an bean matching the given reference, 
74       * or null if there is no bean matching the given reference
75       */
76      public abstract Object getReferenced(Context context, String id);
77      
78      /***
79       * Reset to the initial state.
80       *
81       */
82      public abstract void reset();
83      
84  }