lang/java/mapred/src/main/java/org/apache/avro/mapred/AvroReducer.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.mapred.Reporter;
import org.apache.hadoop.conf.Configured;

/** A reducer for Avro data.
 *
 * <p>Applications should subclass this class and pass their subclass to {@link
 * AvroJob#setReducerClass} and perhaps {@link AvroJob#setCombinerClass}.
 * Subclasses override {@link #reduce}.
 */

public class AvroReducer<K,V,OUT> extends Configured {

  private Pair<K,V> outputPair;

  /** Called with all map output values with a given key.  By default, pairs
   * key with each value, collecting {@link Pair} instances. */
  @SuppressWarnings("unchecked")
  public void reduce(K key, Iterable<V> values,
                     AvroCollector<OUT> collector,
                     Reporter reporter) throws IOException {
    if (outputPair == null)
      outputPair = new Pair<K,V>(AvroJob.getOutputSchema(getConf()));
    for (V value : values) {
      outputPair.set(key, value);
      collector.collect((OUT)outputPair);
    }
  }

}