com.cloudera.crunch.io.seq.SeqFileReaderFactory.java Source code

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Here is the source code for com.cloudera.crunch.io.seq.SeqFileReaderFactory.java

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/**
 * Copyright (c) 2011, Cloudera, Inc. All Rights Reserved.
 *
 * Cloudera, Inc. 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
 *
 * This software 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.cloudera.crunch.io.seq;

import java.io.IOException;
import java.util.Iterator;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
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 com.cloudera.crunch.MapFn;
import com.cloudera.crunch.io.FileReaderFactory;
import com.cloudera.crunch.type.PType;
import com.google.common.collect.Iterators;
import com.google.common.collect.UnmodifiableIterator;

public class SeqFileReaderFactory<T> implements FileReaderFactory<T> {

    private static final Log LOG = LogFactory.getLog(SeqFileReaderFactory.class);

    private final MapFn<Object, T> mapFn;
    private final Writable key;
    private final Writable value;
    private final Configuration conf;

    public SeqFileReaderFactory(PType<T> ptype, Configuration conf) {
        this.mapFn = SeqFileHelper.getInputMapFn(ptype);
        this.key = NullWritable.get();
        this.value = SeqFileHelper.newInstance(ptype, conf);
        this.conf = conf;
    }

    @Override
    public Iterator<T> read(FileSystem fs, final Path path) {
        try {
            final SequenceFile.Reader reader = new SequenceFile.Reader(fs, path, conf);
            return new UnmodifiableIterator<T>() {
                boolean nextChecked = false;
                boolean hasNext = false;

                @Override
                public boolean hasNext() {
                    if (nextChecked == true) {
                        return hasNext;
                    }
                    try {
                        hasNext = reader.next(key, value);
                        nextChecked = true;
                        return hasNext;
                    } catch (IOException e) {
                        LOG.info("Error reading from path: " + path, e);
                        return false;
                    }
                }

                @Override
                public T next() {
                    if (!nextChecked && !hasNext()) {
                        return null;
                    }
                    nextChecked = false;
                    return mapFn.map(value);
                }
            };
        } catch (IOException e) {
            LOG.info("Could not read seqfile at path: " + path, e);
            return Iterators.emptyIterator();
        }
    }

}