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Librares that make easier to solve data problems using Hadoop and higher level languages based on it.
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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 datafu.hourglass.avro;

import java.io.IOException;
import java.io.OutputStream;
import java.util.Map.Entry;

import org.apache.avro.Schema;
import org.apache.avro.hadoop.io.AvroKeyValue;
import org.apache.avro.hadoop.io.AvroDatumConverter;
import org.apache.avro.file.CodecFactory;
import org.apache.avro.file.DataFileWriter;
import org.apache.avro.generic.GenericData;
import org.apache.avro.generic.GenericRecord;
import org.apache.avro.reflect.ReflectDatumWriter;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;

/**
 * Writes key/value pairs to an Avro container file.
 *
 * Each entry in the Avro container file will be a generic record with two fields,
 * named 'key' and 'value'.  The input types may be basic Writable objects like Text or
 * IntWritable, or they may be AvroWrapper subclasses (AvroKey or AvroValue).  Writable
 * objects will be converted to their corresponding Avro types when written to the generic
 * record key/value pair.
 *
 * @param  The type of key to write.
 * @param  The type of value to write.
 */
public class AvroKeyValueWithMetadataRecordWriter extends RecordWriter {
  /** A writer for the Avro container file. */
  private final DataFileWriter mAvroFileWriter;

  /** The writer schema for the generic record entries of the Avro container file. */
  private final Schema mKeyValuePairSchema;

  /** A reusable Avro generic record for writing key/value pairs to the file. */
  private final AvroKeyValue mOutputRecord;

  /** A helper object that converts the input key to an Avro datum. */
  private final AvroDatumConverter mKeyConverter;

  /** A helper object that converts the input value to an Avro datum. */
  private final AvroDatumConverter mValueConverter;

  /** The configuration key prefix for a text output metadata. */
  public static final String TEXT_PREFIX = "avro.meta.text.";
  
  public AvroKeyValueWithMetadataRecordWriter(AvroDatumConverter keyConverter,
      AvroDatumConverter valueConverter, CodecFactory compressionCodec,
      OutputStream outputStream, Configuration conf) throws IOException {
    // Create the generic record schema for the key/value pair.
    mKeyValuePairSchema = AvroKeyValue.getSchema(
        keyConverter.getWriterSchema(), valueConverter.getWriterSchema());

    // Create an Avro container file and a writer to it.
    mAvroFileWriter = new DataFileWriter(
        new ReflectDatumWriter(mKeyValuePairSchema));
    mAvroFileWriter.setCodec(compressionCodec);
    
    for (Entry e : conf)
    {
      if (e.getKey().startsWith(TEXT_PREFIX))
        mAvroFileWriter.setMeta(e.getKey().substring(TEXT_PREFIX.length()),
                                e.getValue());
    }
    
    mAvroFileWriter.create(mKeyValuePairSchema, outputStream);

    // Keep a reference to the converters.
    mKeyConverter = keyConverter;
    mValueConverter = valueConverter;

    // Create a reusable output record.
    mOutputRecord = new AvroKeyValue(new GenericData.Record(mKeyValuePairSchema));
  }

  /**
   * Gets the writer schema for the key/value pair generic record.
   *
   * @return The writer schema used for entries of the Avro container file.
   */
  public Schema getWriterSchema() {
    return mKeyValuePairSchema;
  }

  /** {@inheritDoc} */
  @Override
  public void write(K key, V value) throws IOException {
    mOutputRecord.setKey(mKeyConverter.convert(key));
    mOutputRecord.setValue(mValueConverter.convert(value));
    mAvroFileWriter.append(mOutputRecord.get());
  }

  /** {@inheritDoc} */
  @Override
  public void close(TaskAttemptContext context) throws IOException {
    mAvroFileWriter.close();
  }
}