mapreduce/src/main/java/org/apache/mrql/MapReduceMRQLFileInputFormat.java

/**
 * 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 org.apache.mrql;

import java.io.*;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;


/** A superclass for all MRQL FileInputFormats */
abstract public class MapReduceMRQLFileInputFormat extends FileInputFormat<MRContainer,MRContainer> implements MRQLFileInputFormat {
    public MapReduceMRQLFileInputFormat () {}

    /** record reader for map-reduce */
    abstract public RecordReader<MRContainer,MRContainer>
        createRecordReader ( InputSplit split,
                             TaskAttemptContext context ) throws IOException, InterruptedException;

    /** materialize the input file into a memory Bag */
    abstract public Bag materialize ( final Path path ) throws IOException;

    /** materialize the entire dataset into a Bag
     * @param x the DataSet in HDFS to collect values from
     * @param strip is not used in MapReduce mode
     * @return the Bag that contains the collected values
     */
    public final Bag collect ( final DataSet x, boolean strip ) throws Exception {
        Bag res = new Bag();
        for ( DataSource s: x.source )
            if (s.to_be_merged)
                res = res.union(Plan.merge(s));
            else res = res.union(s.inputFormat.newInstance().materialize(new Path(s.path)));
        return res;
    }
}