001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce.lib.output;
020
021import java.io.IOException;
022import java.util.Arrays;
023
024import org.apache.hadoop.fs.FileSystem;
025import org.apache.hadoop.fs.Path;
026import org.apache.hadoop.fs.FileUtil;
027import org.apache.hadoop.fs.PathFilter;
028
029import org.apache.hadoop.io.MapFile;
030import org.apache.hadoop.io.WritableComparable;
031import org.apache.hadoop.io.Writable;
032import org.apache.hadoop.io.SequenceFile.CompressionType;
033import org.apache.hadoop.io.compress.CompressionCodec;
034import org.apache.hadoop.io.compress.DefaultCodec;
035import org.apache.hadoop.mapreduce.Partitioner;
036import org.apache.hadoop.mapreduce.RecordWriter;
037import org.apache.hadoop.mapreduce.TaskAttemptContext;
038import org.apache.hadoop.util.ReflectionUtils;
039import org.apache.hadoop.classification.InterfaceAudience;
040import org.apache.hadoop.classification.InterfaceStability;
041import org.apache.hadoop.conf.Configuration;
042
043/** 
044 * An {@link org.apache.hadoop.mapreduce.OutputFormat} that writes 
045 * {@link MapFile}s.
046 */
047@InterfaceAudience.Public
048@InterfaceStability.Stable
049public class MapFileOutputFormat 
050    extends FileOutputFormat<WritableComparable<?>, Writable> {
051
052  public RecordWriter<WritableComparable<?>, Writable> getRecordWriter(
053      TaskAttemptContext context) throws IOException {
054    Configuration conf = context.getConfiguration();
055    CompressionCodec codec = null;
056    CompressionType compressionType = CompressionType.NONE;
057    if (getCompressOutput(context)) {
058      // find the kind of compression to do
059      compressionType = SequenceFileOutputFormat.getOutputCompressionType(context);
060
061      // find the right codec
062      Class<?> codecClass = getOutputCompressorClass(context,
063                                  DefaultCodec.class);
064      codec = (CompressionCodec) ReflectionUtils.newInstance(codecClass, conf);
065    }
066
067    Path file = getDefaultWorkFile(context, "");
068    FileSystem fs = file.getFileSystem(conf);
069    // ignore the progress parameter, since MapFile is local
070    final MapFile.Writer out =
071      new MapFile.Writer(conf, fs, file.toString(),
072        context.getOutputKeyClass().asSubclass(WritableComparable.class),
073        context.getOutputValueClass().asSubclass(Writable.class),
074        compressionType, codec, context);
075
076    return new RecordWriter<WritableComparable<?>, Writable>() {
077        public void write(WritableComparable<?> key, Writable value)
078            throws IOException {
079          out.append(key, value);
080        }
081
082        public void close(TaskAttemptContext context) throws IOException { 
083          out.close();
084        }
085      };
086  }
087
088  /** Open the output generated by this format. */
089  public static MapFile.Reader[] getReaders(Path dir,
090      Configuration conf) throws IOException {
091    FileSystem fs = dir.getFileSystem(conf);
092    PathFilter filter = new PathFilter() {
093      @Override
094      public boolean accept(Path path) {
095        String name = path.getName();
096        if (name.startsWith("_") || name.startsWith("."))
097          return false;
098        return true;
099      }
100    };
101    Path[] names = FileUtil.stat2Paths(fs.listStatus(dir, filter));
102
103    // sort names, so that hash partitioning works
104    Arrays.sort(names);
105    
106    MapFile.Reader[] parts = new MapFile.Reader[names.length];
107    for (int i = 0; i < names.length; i++) {
108      parts[i] = new MapFile.Reader(fs, names[i].toString(), conf);
109    }
110    return parts;
111  }
112    
113  /** Get an entry from output generated by this class. */
114  public static <K extends WritableComparable<?>, V extends Writable>
115      Writable getEntry(MapFile.Reader[] readers, 
116      Partitioner<K, V> partitioner, K key, V value) throws IOException {
117    int part = partitioner.getPartition(key, value, readers.length);
118    return readers[part].get(key, value);
119  }
120}
121