org.apache.ibatis.cache.Cache.java Source code

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Here is the source code for org.apache.ibatis.cache.Cache.java

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/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.cache;

import java.util.concurrent.locks.ReadWriteLock;

/**
 * SPI for cache providers.
 * <p>
 * One instance of cache will be created for each namespace.
 * <p>
 * The cache implementation must have a constructor that receives the cache id as an String parameter.
 * <p>
 * MyBatis will pass the namespace as id to the constructor.
 *
 * <pre>
 * public MyCache(final String id) {
 *  if (id == null) {
 *    throw new IllegalArgumentException("Cache instances require an ID");
 *  }
 *  this.id = id;
 *  initialize();
 * }
 * </pre>
 *
 * @author Clinton Begin
 */

public interface Cache {

    /**
     * @return The identifier of this cache
     */
    String getId();

    /**
     * @param key Can be any object but usually it is a {@link CacheKey}
     * @param value The result of a select.
     */
    void putObject(Object key, Object value);

    /**
     * @param key The key
     * @return The object stored in the cache.
     */
    Object getObject(Object key);

    /**
     * As of 3.3.0 this method is only called during a rollback
     * for any previous value that was missing in the cache.
     * This lets any blocking cache to release the lock that
     * may have previously put on the key.
     * A blocking cache puts a lock when a value is null
     * and releases it when the value is back again.
     * This way other threads will wait for the value to be
     * available instead of hitting the database.
     *
     *
     * @param key The key
     * @return Not used
     */
    Object removeObject(Object key);

    /**
     * Clears this cache instance.
     */
    void clear();

    /**
     * Optional. This method is not called by the core.
     *
     * @return The number of elements stored in the cache (not its capacity).
     */
    int getSize();

    /**
     * Optional. As of 3.2.6 this method is no longer called by the core.
     * <p>
     * Any locking needed by the cache must be provided internally by the cache provider.
     *
     * @return A ReadWriteLock
     */
    default ReadWriteLock getReadWriteLock() {
        return null;
    }

}