~~~ 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; } } ~~~