com.zinnia.nectar.util.hadoop.inputformat.FirstNLineInputFormat.java Source code

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Here is the source code for com.zinnia.nectar.util.hadoop.inputformat.FirstNLineInputFormat.java

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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.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 com.zinnia.nectar.util.hadoop.inputformat;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.LineRecordReader;
import org.apache.hadoop.util.LineReader;

/*
 * Its a utility class inspired by the NLineInputFormat of Hadoop. This input format create a InputSpilt of first N line of input file.
 */
public class FirstNLineInputFormat extends FileInputFormat<LongWritable, Text> {

    public static final String LINES_PER_MAP = "mapreduce.input.lineinputformat.linespermap";

    @Override
    public RecordReader<LongWritable, Text> createRecordReader(InputSplit inputSplit, TaskAttemptContext context)
            throws IOException, InterruptedException {
        // TODO Auto-generated method stub
        context.setStatus(inputSplit.toString());
        return new LineRecordReader();
    }

    @Override
    public List<InputSplit> getSplits(JobContext job) throws IOException {
        // TODO Auto-generated method stub
        List<InputSplit> inputSplits = new ArrayList<InputSplit>();
        for (FileStatus status : listStatus(job)) {
            inputSplits.addAll(getSplitsForFile(status, job.getConfiguration(), getNumLinesPerSplit(job)));
        }

        return inputSplits;

    }

    public static List<FileSplit> getSplitsForFile(FileStatus status, Configuration conf, int numLinesPerSplit)
            throws IOException {
        List<FileSplit> splits = new ArrayList<FileSplit>();
        Path fileName = status.getPath();
        FileSystem fs = fileName.getFileSystem(conf);
        LineReader lr = null;
        FSDataInputStream in = fs.open(fileName);
        lr = new LineReader(in, conf);
        Text line = new Text();
        int numLines = 0;
        long begin = 0;
        long length = 0;
        int num = -1;
        while ((num = lr.readLine(line)) > 0) {
            numLines++;
            length += num;
            if (numLines == numLinesPerSplit) {
                // NLineInputFormat uses LineRecordReader, which always reads
                // (and consumes) at least one character out of its upper split
                // boundary. So to make sure that each mapper gets N lines, we
                // move back the upper split limits of each split 
                // by one character here.
                if (begin == 0) {
                    splits.add(new FileSplit(fileName, begin, length - 1, new String[] {}));
                } else {
                    lr.close();
                }
            }
        }
        return splits;
    }

    public static void setNumLinesPerSplit(Job job, int numLines) {
        job.getConfiguration().setInt(LINES_PER_MAP, numLines);
    }

    /**
     * Get the number of lines per split
     * @param job the job
     * @return the number of lines per split
     */
    public static int getNumLinesPerSplit(JobContext job) {
        return job.getConfiguration().getInt(LINES_PER_MAP, 1);
    }
}