org.apache.hadoop.mapreduce.lib.output.MapFileOutputFormat.java Source code

Introduction

Here is the source code for org.apache.hadoop.mapreduce.lib.output.MapFileOutputFormat.java

Source

/**
 * 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.hadoop.mapreduce.lib.output;

import java.io.IOException;
import java.util.Arrays;

import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.FileUtil;
import org.apache.hadoop.fs.PathFilter;

import org.apache.hadoop.io.MapFile;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.SequenceFile.CompressionType;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.DefaultCodec;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;

/** 
 * An {@link org.apache.hadoop.mapreduce.OutputFormat} that writes 
 * {@link MapFile}s.
 */
@InterfaceAudience.Public
@InterfaceStability.Stable
public class MapFileOutputFormat extends FileOutputFormat<WritableComparable<?>, Writable> {

    public RecordWriter<WritableComparable<?>, Writable> getRecordWriter(TaskAttemptContext context)
            throws IOException {
        Configuration conf = context.getConfiguration();
        CompressionCodec codec = null;
        CompressionType compressionType = CompressionType.NONE;
        if (getCompressOutput(context)) {
            // find the kind of compression to do
            compressionType = SequenceFileOutputFormat.getOutputCompressionType(context);

            // find the right codec
            Class<?> codecClass = getOutputCompressorClass(context, DefaultCodec.class);
            codec = (CompressionCodec) ReflectionUtils.newInstance(codecClass, conf);
        }

        Path file = getDefaultWorkFile(context, "");
        FileSystem fs = file.getFileSystem(conf);
        // ignore the progress parameter, since MapFile is local
        final MapFile.Writer out = new MapFile.Writer(conf, fs, file.toString(),
                context.getOutputKeyClass().asSubclass(WritableComparable.class),
                context.getOutputValueClass().asSubclass(Writable.class), compressionType, codec, context);

        return new RecordWriter<WritableComparable<?>, Writable>() {
            public void write(WritableComparable<?> key, Writable value) throws IOException {
                out.append(key, value);
            }

            public void close(TaskAttemptContext context) throws IOException {
                out.close();
            }
        };
    }

    /** Open the output generated by this format. */
    public static MapFile.Reader[] getReaders(Path dir, Configuration conf) throws IOException {
        FileSystem fs = dir.getFileSystem(conf);
        PathFilter filter = new PathFilter() {
            @Override
            public boolean accept(Path path) {
                String name = path.getName();
                if (name.startsWith("_") || name.startsWith("."))
                    return false;
                return true;
            }
        };
        Path[] names = FileUtil.stat2Paths(fs.listStatus(dir, filter));

        // sort names, so that hash partitioning works
        Arrays.sort(names);

        MapFile.Reader[] parts = new MapFile.Reader[names.length];
        for (int i = 0; i < names.length; i++) {
            parts[i] = new MapFile.Reader(fs, names[i].toString(), conf);
        }
        return parts;
    }

    /** Get an entry from output generated by this class. */
    public static <K extends WritableComparable<?>, V extends Writable> Writable getEntry(MapFile.Reader[] readers,
            Partitioner<K, V> partitioner, K key, V value) throws IOException {
        int readerLength = readers.length;
        int part;
        if (readerLength <= 1) {
            part = 0;
        } else {
            part = partitioner.getPartition(key, value, readers.length);
        }
        return readers[part].get(key, value);
    }
}