org.apache.avro.mapred.HadoopCombiner.java Source code

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Here is the source code for org.apache.avro.mapred.HadoopCombiner.java

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/**
 * 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.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<K>(null);
        private final AvroValue<V> valueWrapper = new AvroValue<V>(null);
        private OutputCollector<AvroKey<K>, AvroValue<V>> collector;

        public PairCollector(OutputCollector<AvroKey<K>, AvroValue<V>> collector) {
            this.collector = collector;
        }

        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);
    }

}