MapReduceAvroWordCount.java

/**
 * 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 example;

import java.io.IOException;
import java.util.*;

import org.apache.avro.Schema;
import org.apache.avro.Schema.Type;
import org.apache.avro.mapred.AvroWrapper;
import org.apache.avro.mapred.Pair;
import org.apache.avro.mapreduce.AvroJob;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

/**
 * The classic WordCount example modified to output Avro Pair<CharSequence,
 * Integer> records instead of text.
 */
public class MapReduceAvroWordCount extends Configured implements Tool {

  public static class Map
    extends Mapper<LongWritable, Text, Text, IntWritable> {

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    public void map(LongWritable key, Text value, Context context)
      throws IOException, InterruptedException {
      String line = value.toString();
      StringTokenizer tokenizer = new StringTokenizer(line);
      while (tokenizer.hasMoreTokens()) {
        word.set(tokenizer.nextToken());
        context.write(word, one);
      }
    }
  }

  public static class Reduce
    extends Reducer<Text, IntWritable,
            AvroWrapper<Pair<CharSequence, Integer>>, NullWritable> {

    public void reduce(Text key, Iterable<IntWritable> values,
                       Context context)
      throws IOException, InterruptedException {
      int sum = 0;
      for (IntWritable value : values) {
        sum += value.get();
      }
      context.write(new AvroWrapper<Pair<CharSequence, Integer>>
                    (new Pair<CharSequence, Integer>(key.toString(), sum)),
                    NullWritable.get());
    }
  }

  public int run(String[] args) throws Exception {
    if (args.length != 2) {
      System.err.println("Usage: AvroWordCount <input path> <output path>");
      return -1;
    }

    Job job = new Job(getConf());
    job.setJarByClass(MapReduceAvroWordCount.class);
    job.setJobName("wordcount");

    // We call setOutputSchema first so we can override the configuration
    // parameters it sets
    AvroJob.setOutputKeySchema(job,
                               Pair.getPairSchema(Schema.create(Type.STRING),
                                                  Schema.create(Type.INT)));
    job.setOutputValueClass(NullWritable.class);

    job.setMapperClass(Map.class);
    job.setReducerClass(Reduce.class);

    job.setInputFormatClass(TextInputFormat.class);

    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(IntWritable.class);
    job.setSortComparatorClass(Text.Comparator.class);

    FileInputFormat.setInputPaths(job, new Path(args[0]));
    FileOutputFormat.setOutputPath(job, new Path(args[1]));

    job.waitForCompletion(true);

    return 0;
  }

  public static void main(String[] args) throws Exception {
    int res =
      ToolRunner.run(new Configuration(), new MapReduceAvroWordCount(), args);
    System.exit(res);
  }
}