1 /**
2 * Copyright 2009-2019 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 * 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 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 Can be any object but usually it is a {@link CacheKey}
51 * @param value The result of a select.
52 */
53 void putObject(Object key, Object value);
54
55 /**
56 * @param key The key
57 * @return The object stored in the cache.
58 */
59 Object getObject(Object key);
60
61 /**
62 * As of 3.3.0 this method is only called during a rollback
63 * for any previous value that was missing in the cache.
64 * This lets any blocking cache to release the lock that
65 * may have previously put on the key.
66 * A blocking cache puts a lock when a value is null
67 * and releases it when the value is back again.
68 * This way other threads will wait for the value to be
69 * available instead of hitting the database.
70 *
71 *
72 * @param key The key
73 * @return Not used
74 */
75 Object removeObject(Object key);
76
77 /**
78 * Clears this cache instance.
79 */
80 void clear();
81
82 /**
83 * Optional. This method is not called by the core.
84 *
85 * @return The number of elements stored in the cache (not its capacity).
86 */
87 int getSize();
88
89 /**
90 * Optional. As of 3.2.6 this method is no longer called by the core.
91 * <p>
92 * Any locking needed by the cache must be provided internally by the cache provider.
93 *
94 * @return A ReadWriteLock
95 */
96 default ReadWriteLock getReadWriteLock() {
97 return null;
98 }
99
100 }