    001    /*
    002     * Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved.
    003     *
    004     * Project and contact information: http://www.cascading.org/
    005     *
    006     * This file is part of the Cascading project.
    007     *
    008     * Licensed under the Apache License, Version 2.0 (the "License");
    009     * you may not use this file except in compliance with the License.
    010     * You may obtain a copy of the License at
    011     *
    012     *     http://www.apache.org/licenses/LICENSE-2.0
    013     *
    014     * Unless required by applicable law or agreed to in writing, software
    015     * distributed under the License is distributed on an "AS IS" BASIS,
    016     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    017     * See the License for the specific language governing permissions and
    018     * limitations under the License.
    019     */
    020
    021    package cascading.tuple.collect;
    022
    023    import java.util.Collection;
    024    import java.util.Map;
    025
    026    import cascading.provider.CascadingFactory;
    027    import cascading.tuple.Tuple;
    028
    029    /**
    030     * Interface TupleMapFactory allows developers to plugin alternative implementations of a "tuple map"
    031     * used to back in memory "join" and "co-group" operations. Typically these implementations are
    032     * "spillable", in that to prevent using up all memory in the JVM, after some threshold is met or event
    033     * is triggered, values are persisted to disk.
    034     * <p/>
    035     * The {@link Map} classes returned must take a {@link cascading.tuple.Tuple} as a key, and a {@link Collection} of Tuples as
    036     * a value. Further, {@link Map#get(Object)} must never return {@code null}, but on the first call to get() on the map
    037     * an empty Collection must be created and stored.
    038     * <p/>
    039     * That is, {@link Map#put(Object, Object)} is never called on the map instance internally,
    040     * only {@code map.get(groupTuple).add(valuesTuple)}.
    041     * <p/>
    042     * Using the {@link TupleCollectionFactory} to create the underlying Tuple Collections would allow that aspect
    043     * to be pluggable as well.
    044     * <p/>
    045     * If the Map implementation implements the {@link Spillable} interface, it will receive a {@link Spillable.SpillListener}
    046     * instance that calls back to the appropriate logging mechanism for the platform. This instance should be passed
    047     * down to any child Spillable types, namely an implementation of {@link SpillableTupleList}.
    048     * <p/>
    049     * The default implementation for the Hadoop platform is the {@link cascading.tuple.hadoop.collect.HadoopTupleMapFactory}
    050     * which created a {@link cascading.tuple.hadoop.collect.HadoopSpillableTupleMap} instance.
    051     * <p/>
    052     * The class {@link SpillableTupleMap} may be used as a base class.
    053     *
    054     * @see SpillableTupleMap
    055     * @see cascading.tuple.hadoop.collect.HadoopTupleMapFactory
    056     * @see TupleCollectionFactory
    057     * @see cascading.tuple.hadoop.collect.HadoopTupleCollectionFactory
    058     */
    059    public interface TupleMapFactory<Config> extends CascadingFactory<Config, Map<Tuple, Collection<Tuple>>>
    060      {
    061      String TUPLE_MAP_FACTORY = "cascading.factory.tuple.map.classname";
    062      }