1 /*
2 * Copyright 2009-2023 the original author or authors.
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 * https://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 package org.apache.ibatis.cache;
17
18 import java.util.concurrent.locks.ReadWriteLock;
19
20 /**
21 * SPI for cache providers.
22 * <p>
23 * One instance of cache will be created for each namespace.
24 * <p>
25 * The cache implementation must have a constructor that receives the cache id as an String parameter.
26 * <p>
27 * MyBatis will pass the namespace as id to the constructor.
28 *
29 * <pre>
30 * public MyCache(final String id) {
31 * if (id == null) {
32 * throw new IllegalArgumentException("Cache instances require an ID");
33 * }
34 * this.id = id;
35 * initialize();
36 * }
37 * </pre>
38 *
39 * @author Clinton Begin
40 */
41
42 public interface Cache {
43
44 /**
45 * @return The identifier of this cache
46 */
47 String getId();
48
49 /**
50 * @param key
51 * Can be any object but usually it is a {@link CacheKey}
52 * @param value
53 * The result of a select.
54 */
55 void putObject(Object key, Object value);
56
57 /**
58 * @param key
59 * The key
60 *
61 * @return The object stored in the cache.
62 */
63 Object getObject(Object key);
64
65 /**
66 * As of 3.3.0 this method is only called during a rollback for any previous value that was missing in the cache. This
67 * lets any blocking cache to release the lock that may have previously put on the key. A blocking cache puts a lock
68 * when a value is null and releases it when the value is back again. This way other threads will wait for the value
69 * to be available instead of hitting the database.
70 *
71 * @param key
72 * The key
73 *
74 * @return Not used
75 */
76 Object removeObject(Object key);
77
78 /**
79 * Clears this cache instance.
80 */
81 void clear();
82
83 /**
84 * Optional. This method is not called by the core.
85 *
86 * @return The number of elements stored in the cache (not its capacity).
87 */
88 int getSize();
89
90 /**
91 * Optional. As of 3.2.6 this method is no longer called by the core.
92 * <p>
93 * Any locking needed by the cache must be provided internally by the cache provider.
94 *
95 * @return A ReadWriteLock
96 */
97 default ReadWriteLock getReadWriteLock() {
98 return null;
99 }
100
101 }