org.shaf.core.io.emulator.SequenceWriter.java Source code

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Here is the source code for org.shaf.core.io.emulator.SequenceWriter.java

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/**
 * Copyright 2014-2015 SHAF-WORK
 * 
 * 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 org.shaf.core.io.emulator;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.MRJobConfig;

/**
 * A {@link RecordReader}, which writes key-value pairs to the binary files.
 * 
 * <p>
 * The behavior of the {@code SequenceWriter} is similar to the behavior of the
 * Hadoop IO class {@code SequenceFileOutputFormat}.
 * </p>
 * 
 * <p>
 * The record format:
 * </p>
 * <ul>
 * <li>Key type: <b>Writable</b></li>
 * <li>Value type: <b>Writable</b></li>
 * </ul>
 * 
 * @author Mykola Galushka
 */
public class SequenceWriter extends FileWriter<Writable, Writable> {

    /**
     * The key class.
     */
    private final Class<?> keyClass;

    /**
     * The value class.
     */
    private final Class<?> valueClass;

    /**
     * Constructs a new sequence file writer.
     * 
     * @param config
     *            the writer configuration.
     * @throws IOException
     *             if the writer has failed to initialize.
     */
    public SequenceWriter(Configuration config) throws IOException {
        super(config);

        try {
            this.keyClass = Class.forName(config.get(MRJobConfig.OUTPUT_KEY_CLASS));
            this.valueClass = Class.forName(config.get(MRJobConfig.OUTPUT_VALUE_CLASS));

            super.out.writeUTF(this.keyClass.getCanonicalName());
            super.out.writeUTF(this.valueClass.getCanonicalName());

        } catch (ClassNotFoundException exc) {
            throw new IOException(exc);
        }
    }

    /**
     * Writes a {@link Record record} to the sequence files.
     */
    @Override
    public void writeRecord(Record<Writable, Writable> record) throws IOException {
        record.getKey().write(super.out);
        record.getValue().write(super.out);
    }
}