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/**
 *  Copyright (c) 2011-2013 Terracotta, Inc.
 *  Copyright (c) 2011-2013 Oracle and/or its affiliates.
 *
 *  All rights reserved. Use is subject to license terms.
 */

package javax.cache.integration;

import javax.cache.configuration.CompleteConfiguration;
import java.util.Map;

/**
 * Used when a cache is read-through or when loading data into a cache via the
 * {@link javax.cache.Cache#loadAll(java.util.Set, boolean,
 * CompletionListener)} method.
 *
 * @param  the type of keys handled by this loader
 * @param  the type of values generated by this loader
 * @author Greg Luck
 * @author Yannis Cosmadopoulos
 * @see CompleteConfiguration#isReadThrough()
 * @see CacheWriter
 * @since 1.0
 */
public interface CacheLoader {

  /**
   * Loads an object. Application developers should implement this
   * method to customize the loading of a value for a cache entry. This method
   * is called by a cache when a requested entry is not in the cache. If
   * the object can't be loaded null should be returned.
   *
   * @param key the key identifying the object being loaded
   * @return The value for the entry that is to be stored in the cache or
   *         null if the object can't be loaded
   * @throws CacheLoaderException if there is problem executing the loader.
   */
  V load(K key) throws CacheLoaderException;



  /**
   * Loads multiple objects. Application developers should implement this
   * method to customize the loading of cache entries. This method is called
   * when the requested object is not in the cache. If an object can't be loaded,
   * it is not returned in the resulting map.
   *
   * @param keys keys identifying the values to be loaded
   * @return A map of key, values to be stored in the cache.
   * @throws CacheLoaderException if there is problem executing the loader.
   */
  Map loadAll(Iterable keys) throws CacheLoaderException;
}