FixedWidthRecordReader.java

package com.caseystella.util.common.hadoop.input.fixed;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.Seekable;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.compress.*;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.mapreduce.lib.input.LineRecordReader;

import java.io.IOException;

/**
 * Created by cstella on 9/3/14.
 */
public class FixedWidthRecordReader extends RecordReader<LongWritable, BytesWritable> {
  private static final Log LOG = LogFactory.getLog(LineRecordReader.class);

  private long start;
  private long pos;
  private long end;
  private FixedWidthReader in;
  private FSDataInputStream fileIn;
  private Seekable filePosition;
  private LongWritable key;
  private BytesWritable value;
  private boolean isCompressedInput;
  private Decompressor decompressor;
  private int width;


  public FixedWidthRecordReader(int width) {
      this.width = width;
  }

  public void initialize(InputSplit genericSplit,
                         TaskAttemptContext context
                        ) throws IOException {
    FileSplit split = (FileSplit) genericSplit;
    Configuration job = context.getConfiguration();
    start = split.getStart();
    end = start + split.getLength();
    final Path file = split.getPath();

    // open the file and seek to the start of the split
    final FileSystem fs = file.getFileSystem(job);
    fileIn = fs.open(file);

    CompressionCodec codec = new CompressionCodecFactory(job).getCodec(file);
    if (null!=codec) {
      isCompressedInput = true;
      decompressor = CodecPool.getDecompressor(codec);
      if (codec instanceof SplittableCompressionCodec) {
        final SplitCompressionInputStream cIn =
          ((SplittableCompressionCodec)codec).createInputStream(
            fileIn, decompressor, start, end,
            SplittableCompressionCodec.READ_MODE.BYBLOCK);
          in = new FixedWidthReader(cIn);

        start = cIn.getAdjustedStart();
        end = cIn.getAdjustedEnd();
        filePosition = cIn;
      } else {
          in = new FixedWidthReader(codec.createInputStream(fileIn, decompressor));

        filePosition = fileIn;
      }
    } else {
      fileIn.seek(start);
        in = new FixedWidthReader(fileIn);

      filePosition = fileIn;
    }
    // If this is not the first split, we always throw away first record
    // because we always (except the last split) read one extra line in
    // next() method.
    if (start != 0) {
      start += in.readLine(new BytesWritable(new byte[width]));
    }
    this.pos = start;
  }



  private long getFilePosition() throws IOException {
    long retVal;
    if (isCompressedInput && null != filePosition) {
      retVal = filePosition.getPos();
    } else {
      retVal = pos;
    }
    return retVal;
  }

  public boolean nextKeyValue() throws IOException {
    if (key == null) {
      key = new LongWritable();
    }
    key.set(pos);
    if (value == null) {
      value = new BytesWritable(new byte[width]);
    }
    int newSize = in.readLine(value);
    pos += newSize;
    if (newSize < width) {
      key = null;
      value = null;
      return false;
    } else {
      return true;
    }
  }

  @Override
  public LongWritable getCurrentKey() {
    return key;
  }

  @Override
  public BytesWritable getCurrentValue() {
    return value;
  }

  /**
   * Get the progress within the split
   */
  public float getProgress() throws IOException {
    if (start == end) {
      return 0.0f;
    } else {
      return Math.min(1.0f, (getFilePosition() - start) / (float)(end - start));
    }
  }

  public synchronized void close() throws IOException {
    try {
      if (in != null) {
        in.close();
      }
    } finally {
      if (decompressor != null) {
        CodecPool.returnDecompressor(decompressor);
      }
    }
  }
}