content: /*
   * 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
   *
   *     https://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.mapred.JobConf;
  import org.apache.hadoop.mapred.OutputCollector;
  import org.apache.hadoop.util.ReflectionUtils;
  
  /**
   * Bridge between a {@link org.apache.hadoop.mapred.Reducer} and an
   * {@link AvroReducer} used when combining. When combining, map output pairs
   * must be split before they're collected.
   */
  class HadoopCombiner<K, V> extends HadoopReducerBase<K, V, Pair<K, V>, AvroKey<K>, AvroValue<V>> {
  
    @Override
    @SuppressWarnings("unchecked")
    protected AvroReducer<K, V, Pair<K, V>> getReducer(JobConf conf) {
      return ReflectionUtils.newInstance(conf.getClass(AvroJob.COMBINER, AvroReducer.class, AvroReducer.class), conf);
    }
  
    private class PairCollector extends AvroCollector<Pair<K, V>> {
      private final AvroKey<K> keyWrapper = new AvroKey<>(null);
      private final AvroValue<V> valueWrapper = new AvroValue<>(null);
      private OutputCollector<AvroKey<K>, AvroValue<V>> collector;
  
      public PairCollector(OutputCollector<AvroKey<K>, AvroValue<V>> collector) {
        this.collector = collector;
      }
  
      @Override
      public void collect(Pair<K, V> datum) throws IOException {
        keyWrapper.datum(datum.key()); // split the Pair
        valueWrapper.datum(datum.value());
        collector.collect(keyWrapper, valueWrapper);
      }
    }
  
    @Override
    protected AvroCollector<Pair<K, V>> getCollector(OutputCollector<AvroKey<K>, AvroValue<V>> collector) {
      return new PairCollector(collector);
    }
  
  }
  