com.bah.culvert.hive.CulvertRecordReader.java Source code

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Here is the source code for com.bah.culvert.hive.CulvertRecordReader.java

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/**
 * Copyright 2011 Booz Allen Hamilton.
 * 
 * See the NOTICE file distributed with this work for additional
 * information regarding copyright ownership. Booz Allen Hamilton
 * 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 com.bah.culvert.hive;

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

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapred.RecordReader;

import com.bah.culvert.data.Result;

/**
 * Read a row from a culvert data table using the specified value in the index
 * table.
 */
public class CulvertRecordReader implements RecordReader<NullWritable, Result> {

    private static final Log LOG = LogFactory.getLog(CulvertRecordReader.class);
    private final Iterator<Result> indexIterator;
    private long currentKeyCount = 0;

    /**
     * Create a Culvert record reader that uses the indexes in the split to read
     * records from the specified data table
     * 
     * @param split to read index information
     * @throws IOException on failure to read from the index table
     */
    public CulvertRecordReader(CulvertInputSplit split) throws IOException {
        // actually do the get on the indicies
        this.indexIterator = split.getQueryConstraint().getResultIterator();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.hadoop.mapred.RecordReader#close()
     */
    @Override
    public void close() throws IOException {
        // NOOP
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.hadoop.mapred.RecordReader#createValue()
     */
    @Override
    public Result createValue() {
        return new Result();
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.hadoop.mapred.RecordReader#getPos()
     */
    @Override
    public long getPos() throws IOException {
        return currentKeyCount;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.hadoop.mapred.RecordReader#getProgress()
     */
    @Override
    public float getProgress() throws IOException {
        return 0;
    }

    /*
     * (non-Javadoc)
     * 
     * @see org.apache.hadoop.mapred.RecordReader#next(java.lang.Object,
     * java.lang.Object)
     */
    @Override
    public boolean next(NullWritable key, Result row) throws IOException {
        // if there are more indexed rows, we want to get them
        if (indexIterator.hasNext()) {
            // update the number of keys gotten
            this.currentKeyCount++;

            // don't think that we need to actually handle getting the value - this
            // should be taken care of by the input splits
            Result newResult = indexIterator.next();
            // set the data row id
            row.copy(newResult);
            return indexIterator.hasNext();
        } else {
            throw new IOException("Out of results.");
        }
    }

    @Override
    public NullWritable createKey() {
        return NullWritable.get();
    }
}