com.splout.db.hadoop.SchemaSampler.java Source code

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Here is the source code for com.splout.db.hadoop.SchemaSampler.java

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package com.splout.db.hadoop;

/*
 * #%L
 * Splout SQL Hadoop library
 * %%
 * Copyright (C) 2012 - 2013 Datasalt Systems S.L.
 * %%
 * 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.
 * #L%
 */

import com.datasalt.pangool.io.ITuple;
import com.datasalt.pangool.io.Schema;
import com.datasalt.pangool.utils.TaskAttemptContextFactory;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

import java.io.IOException;
import java.util.List;

/**
 * Small piece of code that can sample a Pangool Schema from an arbitrary InputFormat<ITuple, NullWritable>. It just
 * reads the first Tuple and reads the Schema from it.
 */
public class SchemaSampler {

    private final static Log log = LogFactory.getLog(SchemaSampler.class);

    public static Schema sample(Configuration conf, Path input, InputFormat<ITuple, NullWritable> inputFormat)
            throws IOException, InterruptedException {
        Schema schema = null;

        // sample schema from input path given the provided InputFormat
        @SuppressWarnings("deprecation")
        Job job = new Job(conf);
        FileInputFormat.setInputPaths(job, input);
        // get first inputSplit
        List<InputSplit> inputSplits = inputFormat.getSplits(job);
        if (inputSplits == null || inputSplits.size() == 0) {
            throw new IOException(
                    "Given input format doesn't produce any input split. Can't sample first record. PATH: "
                            + input);
        }
        InputSplit inputSplit = inputSplits.get(0);
        TaskAttemptID attemptId = new TaskAttemptID(new TaskID(), 1);
        TaskAttemptContext attemptContext;
        try {
            attemptContext = TaskAttemptContextFactory.get(conf, attemptId);
        } catch (Exception e) {
            throw new IOException(e);
        }

        RecordReader<ITuple, NullWritable> rReader = inputFormat.createRecordReader(inputSplit, attemptContext);
        rReader.initialize(inputSplit, attemptContext);

        if (!rReader.nextKeyValue()) {
            throw new IOException(
                    "Can't read first record of first input split of the given path [" + input + "].");
        }

        // finally get the sample schema
        schema = rReader.getCurrentKey().getSchema();
        log.info("Sampled schema from [" + input + "] : " + schema);
        rReader.close();

        return schema;
    }
}