org.apache.mahout.classifier.sequencelearning.hmm.hadoop.MapWritableCache.java Source code

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Here is the source code for org.apache.mahout.classifier.sequencelearning.hmm.hadoop.MapWritableCache.java

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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.mahout.classifier.sequencelearning.hmm.hadoop;

import java.io.IOException;
import java.net.URI;

import com.google.common.io.Closeables;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.filecache.DistributedCache;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.*;
import org.apache.mahout.common.HadoopUtil;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Writable;
import org.apache.mahout.common.iterator.sequencefile.SequenceFileValueIterator;

/**
 * This class handles reading and writing MapWritable to DistributedCache
 */
public final class MapWritableCache {

    private MapWritableCache() {
    }

    /**
     * Wraps a (Key, MapWritable) into a sequence file and stores it to the specified directory.
     *
     * @param key           key of the SequenceFile
     * @param map           MapWritable to be stored
     * @param output        directory where the sequence file should be stored
     * @param conf          configuration
     * @param overwritePath if true, overwrite the file present in the output directory
     * @param deleteOnExit  if true. deletes the map on exiting
     * @throws IOException
     */
    public static void save(Writable key, MapWritable map, Path output, Configuration conf, boolean overwritePath,
            boolean deleteOnExit) throws IOException {

        FileSystem fs = FileSystem.get(conf);
        output = fs.makeQualified(output);
        if (overwritePath) {
            HadoopUtil.delete(conf, output);
        }

        // set the cache
        DistributedCache.setCacheFiles(new URI[] { output.toUri() }, conf);

        // set up the writer
        SequenceFile.Writer writer = new SequenceFile.Writer(fs, conf, output, IntWritable.class,
                MapWritable.class);
        try {
            writer.append(key, new MapWritable(map));
        } finally {
            Closeables.closeQuietly(writer);
        }

        if (deleteOnExit) {
            fs.deleteOnExit(output);
        }
    }

    /**
     * Calls the save() method, setting the cache to overwrite any previous
     * Path and to delete the path after exiting
     *
     * @param key    sequence file Key
     * @param map    MapWritable stored
     * @param output path to the directory to store the sequence file
     * @param conf   configuration object
     * @throws IOException
     */
    public static void save(Writable key, MapWritable map, Path output, Configuration conf) throws IOException {
        save(key, map, output, conf, true, true);
    }

    /**
     * Loads a MapWritable from {@link DistributedCache}. Returns null if no map exists.
     */
    public static MapWritable load(Configuration conf) throws IOException {
        URI[] files = DistributedCache.getCacheFiles(conf);
        if (files == null || files.length < 1) {
            return null;
        }
        return load(conf, new Path(files[0].getPath()));
    }

    /**
     * Loads a MapWritable from the specified path. Returns null if no map exists.
     *
     * @param conf  configuration object
     * @param input path of the MapWritable in {@link DistributedCache}
     * @return MapWritable
     * @throws IOException
     */
    public static MapWritable load(Configuration conf, Path input) throws IOException {
        SequenceFileValueIterator<MapWritable> iterator = new SequenceFileValueIterator<MapWritable>(input, true,
                conf);
        try {
            return iterator.next();
        } finally {
            Closeables.closeQuietly(iterator);
        }
    }

}