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A pure Java 8 port of Facebook Dataloader
There is a newer version: 2022-09-12T23-25-35-08559ba
/*
 * Copyright (c) 2016 The original author or authors
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 *
 *      The Eclipse Public License is available at
 *      http://www.eclipse.org/legal/epl-v10.html
 *
 *      The Apache License v2.0 is available at
 *      http://www.opensource.org/licenses/apache2.0.php
 *
 * You may elect to redistribute this code under either of these licenses.
 */

package org.dataloader;

import org.dataloader.annotations.PublicSpi;
import org.dataloader.impl.DefaultCacheMap;

import java.util.Collection;
import java.util.concurrent.CompletableFuture;

/**
 * CacheMap is used by data loaders that use caching promises to values aka {@link CompletableFuture}<V>.  A better name for this
 * class might have been FutureCache but that is history now.
 * 
 * The default implementation used by the data loader is based on a {@link java.util.LinkedHashMap}.
 * 

 * This is really a cache of completed {@link CompletableFuture}<V> values in memory.  It is used, when caching is enabled, to
 * give back the same future to any code that may call it.  If you need a cache of the underlying values that is possible external to the JVM
 * then you will want to use {{@link ValueCache}} which is designed for external cache access.
 *
 * @param  type parameter indicating the type of the cache keys
 * @param  type parameter indicating the type of the data that is cached
 *
 * @author Arnold Schrijver
 * @author Brad Baker
 */
@PublicSpi
public interface CacheMap {

    /**
     * Creates a new cache map, using the default implementation that is based on a {@link java.util.LinkedHashMap}.
     *
     * @param  type parameter indicating the type of the cache keys
     * @param  type parameter indicating the type of the data that is cached
     *
     * @return the cache map
     */
    static  CacheMap simpleMap() {
        return new DefaultCacheMap<>();
    }

    /**
     * Checks whether the specified key is contained in the cache map.
     *
     * @param key the key to check
     *
     * @return {@code true} if the cache contains the key, {@code false} otherwise
     */
    boolean containsKey(K key);

    /**
     * Gets the specified key from the cache map.
     * 
     * May throw an exception if the key does not exist, depending on the cache map implementation that is used,
     * so be sure to check {@link CacheMap#containsKey(Object)} first.
     *
     * @param key the key to retrieve
     *
     * @return the cached value, or {@code null} if not found (depends on cache implementation)
     */
    CompletableFuture get(K key);

    /**
     * Gets a collection of CompletableFutures from the cache map.
     * @return the collection of cached values
     */
    Collection> getAll();

    /**
     * Creates a new cache map entry with the specified key and value, or updates the value if the key already exists.
     *
     * @param key   the key to cache
     * @param value the value to cache
     *
     * @return the cache map for fluent coding
     */
    CacheMap set(K key, CompletableFuture value);

    /**
     * Deletes the entry with the specified key from the cache map, if it exists.
     *
     * @param key the key to delete
     *
     * @return the cache map for fluent coding
     */
    CacheMap delete(K key);

    /**
     * Clears all entries of the cache map
     *
     * @return the cache map for fluent coding
     */
    CacheMap clear();
}