net.myrrix.batch.common.iterator.sequencefile.SequenceFileIterator.java Source code

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Here is the source code for net.myrrix.batch.common.iterator.sequencefile.SequenceFileIterator.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 net.myrrix.batch.common.iterator.sequencefile;

import java.io.Closeable;
import java.io.IOException;

import com.google.common.collect.AbstractIterator;
import org.apache.commons.math3.util.Pair;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.util.ReflectionUtils;

/**
 * <p>{@link java.util.Iterator} over a {@link SequenceFile}'s keys and values, as a {@link Pair}
 * containing key and value.</p>
 * 
 * @author Sean Owen
 * @author Mahout
 * @since 1.0
 * @param <K> file key class
 * @param <V> file value class
 */
public final class SequenceFileIterator<K extends Writable, V extends Writable> extends AbstractIterator<Pair<K, V>>
        implements Closeable {

    private final SequenceFile.Reader reader;
    private final Configuration conf;
    private final Class<K> keyClass;
    private final Class<V> valueClass;
    private final boolean noValue;
    private K key;
    private V value;
    private final boolean reuseKeyValueInstances;

    /**
     * @throws IOException if path can't be read, or its key or value class can't be instantiated
     */
    public SequenceFileIterator(Path path, boolean reuseKeyValueInstances, Configuration conf) throws IOException {
        FileSystem fs = path.getFileSystem(conf);
        reader = new SequenceFile.Reader(fs, path, conf);
        this.conf = conf;
        @SuppressWarnings("unchecked")
        Class<K> theKeyClass = (Class<K>) reader.getKeyClass();
        keyClass = theKeyClass;
        @SuppressWarnings("unchecked")
        Class<V> theValueClass = (Class<V>) reader.getValueClass();
        valueClass = theValueClass;
        noValue = NullWritable.class.equals(valueClass);
        this.reuseKeyValueInstances = reuseKeyValueInstances;
    }

    public Class<K> getKeyClass() {
        return keyClass;
    }

    public Class<V> getValueClass() {
        return valueClass;
    }

    @Override
    public void close() throws IOException {
        reader.close();
        endOfData();
    }

    @Override
    protected Pair<K, V> computeNext() {
        if (!reuseKeyValueInstances || value == null) {
            key = ReflectionUtils.newInstance(keyClass, conf);
            if (!noValue) {
                value = ReflectionUtils.newInstance(valueClass, conf);
            }
        }
        try {
            boolean available;
            if (noValue) {
                available = reader.next(key);
            } else {
                available = reader.next(key, value);
            }
            if (!available) {
                close();
                return null;
            }
            return new Pair<K, V>(key, value);
        } catch (IOException ioe) {
            try {
                close();
            } catch (IOException ignored) {
                // continue
            }
            throw new IllegalStateException(ioe);
        }
    }

}