    001/*
    002 * Copyright (c) 2007-2017 Xplenty, 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
    021package cascading.tap.hadoop;
    022
    023import java.io.IOException;
    024import java.net.URI;
    025
    026import cascading.flow.FlowProcess;
    027import org.apache.hadoop.conf.Configuration;
    028import org.apache.hadoop.filecache.DistributedCache;
    029import org.apache.hadoop.fs.Path;
    030
    031/**
    032 * Class DistCacheTap is a Tap decorator for Hfs and can be used to move a file to the
    033 * {@link org.apache.hadoop.filecache.DistributedCache} on read when accessed cluster side.
    034 * <p/>
    035 * This is useful for {@link cascading.pipe.HashJoin}s.
    036 * <p/>
    037 * The distributed cache is only used when the Tap is used as a source. If the DistCacheTap is used as a sink,
    038 * it will delegate to the provided parent instance and not use the DistributedCache.
    039 */
    040public class DistCacheTap extends BaseDistCacheTap
    041  {
    042  /**
    043   * Constructs a new DistCacheTap instance with the given Hfs.
    044   *
    045   * @param parent an Hfs or GlobHfs instance representing a small file.
    046   */
    047  public DistCacheTap( Hfs parent )
    048    {
    049    super( parent );
    050    }
    051
    052  @Override
    053  protected Path[] getLocalCacheFiles( FlowProcess<? extends Configuration> flowProcess ) throws IOException
    054    {
    055    return DistributedCache.getLocalCacheFiles( flowProcess.getConfig() );
    056    }
    057
    058  @Override
    059  protected void addLocalCacheFiles( Configuration conf, URI uri )
    060    {
    061    DistributedCache.addCacheFile( uri, conf );
    062    }
    063  }