com.moz.fiji.mapreduce.reducer.IdentityReducer.java Source code

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Here is the source code for com.moz.fiji.mapreduce.reducer.IdentityReducer.java

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/**
 * (c) Copyright 2012 WibiData, Inc.
 *
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership.
 *
 * Licensed 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 com.moz.fiji.mapreduce.reducer;

import java.io.IOException;

import org.apache.avro.Schema;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.util.ReflectionUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.moz.fiji.annotations.ApiAudience;
import com.moz.fiji.annotations.ApiStability;
import com.moz.fiji.mapreduce.FijiReducer;
import com.moz.fiji.mapreduce.avro.AvroKeyWriter;
import com.moz.fiji.mapreduce.avro.AvroValueWriter;

/**
 * This MapReduce reducer will pass through all of the input key-value
 * pairs unchanged.  This differs from the basic Hadoop MapReduce
 * IdentityReducer only in that it extends FijiReducer so it can be
 * run within the Fiji framework.
 *
 * This class implements the {@link AvroKeyWriter} and the {@link AvroValueWriter} interfaces
 * so that it can be used for Avro output
 *
 * @param <K> The MapReduce input key type.
 * @param <V> The MapReduce input value type.
 */
@ApiAudience.Public
@ApiStability.Stable
public final class IdentityReducer<K, V> extends FijiReducer<K, V, K, V>
        implements Configurable, AvroKeyWriter, AvroValueWriter {
    private static final Logger LOG = LoggerFactory.getLogger(IdentityReducer.class);

    /** The Hadoop configuration. */
    private Configuration mConf;

    /** {@inheritDoc} */
    @Override
    public void setConf(Configuration conf) {
        mConf = conf;
    }

    /** {@inheritDoc} */
    @Override
    public Configuration getConf() {
        return mConf;
    }

    /** {@inheritDoc} */
    @Override
    protected void reduce(K key, Iterable<V> values, Context context) throws IOException, InterruptedException {
        for (V value : values) {
            context.write(key, value);
        }
    }

    /** {@inheritDoc} */
    @Override
    public Class<?> getOutputKeyClass() {
        return new JobConf(getConf()).getMapOutputKeyClass();
    }

    /** {@inheritDoc} */
    @Override
    public Class<?> getOutputValueClass() {
        return new JobConf(getConf()).getMapOutputValueClass();
    }

    /** {@inheritDoc} */
    @Override
    public Schema getAvroKeyWriterSchema() throws IOException {
        Class<? extends Mapper<?, ?, ?, ?>> mapperClass;
        try {
            mapperClass = new Job(getConf()).getMapperClass();
        } catch (ClassNotFoundException e) {
            throw new IOException("Mapper class was not configured. " + "Could not infer avro key writer schema.",
                    e);
        }
        Mapper<?, ?, ?, ?> mapper = ReflectionUtils.newInstance(mapperClass, getConf());
        if (mapper instanceof AvroKeyWriter) {
            LOG.info("Mapper is an AvroKeyWriter. Using the same schema for Reducer output keys.");
            return ((AvroKeyWriter) mapper).getAvroKeyWriterSchema();
        }
        return null;
    }

    /** {@inheritDoc} */
    @Override
    public Schema getAvroValueWriterSchema() throws IOException {
        Class<? extends Mapper<?, ?, ?, ?>> mapperClass;
        try {
            mapperClass = new Job(getConf()).getMapperClass();
        } catch (ClassNotFoundException e) {
            throw new IOException("Mapper class was not configured. " + "Could not infer avro value writer schema.",
                    e);
        }
        Mapper<?, ?, ?, ?> mapper = ReflectionUtils.newInstance(mapperClass, getConf());
        if (mapper instanceof AvroValueWriter) {
            LOG.info("Mapper is an AvroValueWriter. Using the same schema for Reducer output values.");
            return ((AvroValueWriter) mapper).getAvroValueWriterSchema();
        }
        return null;
    }
}