lang/java/mapred/src/main/java/org/apache/avro/mapred/HadoopMapper.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 org.apache.avro.mapred;

import java.io.IOException;

import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.util.ReflectionUtils;

/** Bridge between a {@link org.apache.hadoop.mapred.Mapper} and an {@link
 * AvroMapper}.  Outputs are written directly when a job is map-only, but are
 * otherwise assumed to be pairs that are split. */
class HadoopMapper<IN,OUT,K,V,KO,VO> extends MapReduceBase
  implements Mapper<AvroWrapper<IN>, NullWritable, KO, VO> {
    
  private AvroMapper<IN,OUT> mapper;
  private MapCollector out;
  private boolean isMapOnly;

  @Override @SuppressWarnings("unchecked")
  public void configure(JobConf conf) {
    this.mapper =
      ReflectionUtils.newInstance
      (conf.getClass(AvroJob.MAPPER, AvroMapper.class, AvroMapper.class),
       conf);
    this.isMapOnly = conf.getNumReduceTasks() == 0;
  }

  @SuppressWarnings("unchecked")
  private class MapCollector extends AvroCollector<OUT> {
    private final AvroWrapper<OUT> wrapper = new AvroWrapper<OUT>(null);
    private final AvroKey<K> keyWrapper = new AvroKey(null);
    private final AvroValue<V> valueWrapper = new AvroValue(null);
    private OutputCollector<KO,VO> collector;

    public MapCollector(OutputCollector<KO,VO> collector) {
      this.collector = collector;
    }

    public void collect(OUT datum) throws IOException {
      if (isMapOnly) {
        wrapper.datum(datum);
        collector.collect((KO)wrapper, (VO)NullWritable.get());
      } else {                                    // split a pair
        Pair<K,V> pair = (Pair<K,V>)datum;
        keyWrapper.datum(pair.key());
        valueWrapper.datum(pair.value());
        collector.collect((KO)keyWrapper, (VO)valueWrapper);
      }
    }
  }

  @Override
  public void map(AvroWrapper<IN> wrapper, NullWritable value, 
                  OutputCollector<KO,VO> collector, 
                  Reporter reporter) throws IOException {
    if (this.out == null)
      this.out = new MapCollector(collector);
    mapper.map(wrapper.datum(), out, reporter);
  }

}