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Java > Open Source Codes > org > apache > ojb > broker > cache > ObjectCache


1 package org.apache.ojb.broker.cache;
2
3 /* Copyright 2002-2005 The Apache Software Foundation
4  *
5  * Licensed under the Apache License, Version 2.0 (the "License");
6  * you may not use this file except in compliance with the License.
7  * 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 import org.apache.ojb.broker.Identity;
19
20 /**
21  * The <code>ObjectCache</code> stores all Objects loaded by the
22  * {@link org.apache.ojb.broker.PersistenceBroker} from a DB.
23  * When the PersistenceBroker tries to get an Object by its Primary key values
24  * it first lookups the cache if the object has been already loaded and cached.
25  * <br/><br/>
26  * Using an ObjectCache has several advantages:
27  * - it increases performance as it reduces DB lookups.
28  * - it allows to perform circular lookups (as by crossreferenced objects)
29  * that would result in non-terminating loops without such a cache. This will be internally handled by OJB, no
30  * need to take care of this.
31  * - it maintains the uniqueness of objects as any Db row will be mapped to
32  * exactly one object.
33  * <br/><br/>
34  * This interface allows to have userdefined Cache implementations.
35  * The ObjectCacheFactory is responsible for generating cache instances.
36  * by default it uses the OJB {@link ObjectCacheDefaultImpl}.
37  * <br/><br/>
38  * <b>Note:</b> Each {@link org.apache.ojb.broker.PersistenceBroker} was
39  * associated with its own <code>ObjectCache</code> instance at creation
40  * time.
41  * <br/>
42  * {@link ObjectCacheFactory} is responsible for creating <code>ObjectCache</code>
43  * instances. To make the <code>ObjectCache</code> implementation work, a
44  * constructor with {@link org.apache.ojb.broker.PersistenceBroker} and
45  * {@link java.util.Properties} as arguments or only <code>PersistenceBroker</code>
46  * argument is needed.
47  *
48  * @author <a HREF="mailto:thma@apache.org">Thomas Mahler<a>
49  * @author <a HREF="mailto:armin@codeaulait.de">Armin Waibel<a>
50  *
51  * @version $Id: ObjectCache.java,v 1.9.2.3 2005/12/21 22:24:15 tomdz Exp $
52  */
53 public interface ObjectCache
54 {
55     /**
56      * Used to cache objects by it's {@link org.apache.ojb.broker.Identity}.
57      *
58      * @param oid Identity of the object to cache.
59      * @param obj The object to cache.
60      */
61     public void cache(Identity oid, Object JavaDoc obj);
62
63     /**
64      * Lookup object with Identity 'oid' in cache.
65      *
66      * @param oid Identity of the object to search for.
67      * @return The cached object or <em>null</em> if no matching object for
68      * specified {@link org.apache.ojb.broker.Identity} is found.
69      */
70     public Object JavaDoc lookup(Identity oid);
71
72     /**
73      * Removes an Object from the cache.
74      *
75      * @param oid Identity of the object to be removed.
76      */
77     public void remove(Identity oid);
78
79     /**
80      * Clear the cache.
81      */
82     public void clear();
83 }
84
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