001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce.lib.input;
020
021import java.io.IOException;
022import java.io.DataInput;
023import java.io.DataOutput;
024
025import org.apache.hadoop.mapreduce.InputFormat;
026import org.apache.hadoop.mapreduce.InputSplit;
027import org.apache.hadoop.mapreduce.TaskAttemptContext;
028import org.apache.hadoop.classification.InterfaceAudience;
029import org.apache.hadoop.classification.InterfaceStability;
030import org.apache.hadoop.fs.Path;
031import org.apache.hadoop.io.Text;
032import org.apache.hadoop.io.Writable;
033
034/** A section of an input file.  Returned by {@link
035 * InputFormat#getSplits(JobContext)} and passed to
036 * {@link InputFormat#createRecordReader(InputSplit,TaskAttemptContext)}. */
037@InterfaceAudience.Public
038@InterfaceStability.Stable
039public class FileSplit extends InputSplit implements Writable {
040  private Path file;
041  private long start;
042  private long length;
043  private String[] hosts;
044
045  public FileSplit() {}
046
047  /** Constructs a split with host information
048   *
049   * @param file the file name
050   * @param start the position of the first byte in the file to process
051   * @param length the number of bytes in the file to process
052   * @param hosts the list of hosts containing the block, possibly null
053   */
054  public FileSplit(Path file, long start, long length, String[] hosts) {
055    this.file = file;
056    this.start = start;
057    this.length = length;
058    this.hosts = hosts;
059  }
060 
061  /** The file containing this split's data. */
062  public Path getPath() { return file; }
063  
064  /** The position of the first byte in the file to process. */
065  public long getStart() { return start; }
066  
067  /** The number of bytes in the file to process. */
068  @Override
069  public long getLength() { return length; }
070
071  @Override
072  public String toString() { return file + ":" + start + "+" + length; }
073
074  ////////////////////////////////////////////
075  // Writable methods
076  ////////////////////////////////////////////
077
078  @Override
079  public void write(DataOutput out) throws IOException {
080    Text.writeString(out, file.toString());
081    out.writeLong(start);
082    out.writeLong(length);
083  }
084
085  @Override
086  public void readFields(DataInput in) throws IOException {
087    file = new Path(Text.readString(in));
088    start = in.readLong();
089    length = in.readLong();
090    hosts = null;
091  }
092
093  @Override
094  public String[] getLocations() throws IOException {
095    if (this.hosts == null) {
096      return new String[]{};
097    } else {
098      return this.hosts;
099    }
100  }
101}