edu.umn.cs.spatialHadoop.operations.Head.java Source code

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Here is the source code for edu.umn.cs.spatialHadoop.operations.Head.java

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/***********************************************************************
* Copyright (c) 2015 by Regents of the University of Minnesota.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Apache License, Version 2.0 which 
* accompanies this distribution and is available at
* http://www.opensource.org/licenses/apache2.0.php.
*
*************************************************************************/
package edu.umn.cs.spatialHadoop.operations;

import java.io.IOException;

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.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.TaskAttemptID;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.LineRecordReader;
import org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl;

import edu.umn.cs.spatialHadoop.indexing.RTree;

/**
 * Reads the first n lines of a text file
 * @author Ahmed Eldawy
 *
 */
public class Head {

    /**
     * Reads a maximum of n lines from the given file.
     * @param fs
     * @param p
     * @param n
     * @return
     * @throws IOException
     */
    public static String[] head(FileSystem fs, Path p, int n) throws IOException {
        String[] lines = new String[n];
        FileStatus fstatus = fs.getFileStatus(p);

        TaskAttemptContext context = createDummyContext();
        LineRecordReader lineReader = new LineRecordReader();
        FileSplit split;
        if (p.getName().endsWith(".rtree")) {
            // R-tree indexed file
            FSDataInputStream in = fs.open(p);
            in.skip(8); // Skip R-tree signature
            int treeHeaderSize = RTree.skipHeader(in);
            in.close();
            split = new FileSplit(p, treeHeaderSize + 8, fstatus.getLen() - treeHeaderSize - 8, new String[0]);
        } else {
            split = new FileSplit(p, 0, fstatus.getLen(), new String[0]);
        }
        lineReader.initialize(split, context);
        int numOfLines = 0;
        for (numOfLines = 0; numOfLines < lines.length && lineReader.nextKeyValue(); numOfLines++) {
            lines[numOfLines] = lineReader.getCurrentValue().toString();
        }
        lineReader.close();

        return lines;
    }

    private static TaskAttemptContext createDummyContext() {
        TaskAttemptID taskId = new TaskAttemptID();
        return new TaskAttemptContextImpl(new Configuration(), taskId);
    }
}