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 */
018package org.apache.hadoop.mapreduce.lib.input;
019
020import java.io.IOException;
021
022import org.apache.hadoop.classification.InterfaceAudience;
023import org.apache.hadoop.classification.InterfaceStability;
024import org.apache.hadoop.conf.Configuration;
025import org.apache.hadoop.fs.Path;
026import org.apache.hadoop.io.BytesWritable;
027import org.apache.hadoop.io.LongWritable;
028import org.apache.hadoop.io.compress.CompressionCodec;
029import org.apache.hadoop.io.compress.CompressionCodecFactory;
030import org.apache.hadoop.mapreduce.InputSplit;
031import org.apache.hadoop.mapreduce.JobContext;
032import org.apache.hadoop.mapreduce.RecordReader;
033import org.apache.hadoop.mapreduce.TaskAttemptContext;
034
035/**
036 * FixedLengthInputFormat is an input format used to read input files
037 * which contain fixed length records.  The content of a record need not be
038 * text.  It can be arbitrary binary data.  Users must configure the record
039 * length property by calling:
040 * FixedLengthInputFormat.setRecordLength(conf, recordLength);<br><br> or
041 * conf.setInt(FixedLengthInputFormat.FIXED_RECORD_LENGTH, recordLength);
042 * <br><br>
043 * @see FixedLengthRecordReader
044 */
045@InterfaceAudience.Public
046@InterfaceStability.Stable
047public class FixedLengthInputFormat
048    extends FileInputFormat<LongWritable, BytesWritable> {
049
050  public static final String FIXED_RECORD_LENGTH =
051      "fixedlengthinputformat.record.length"; 
052
053  /**
054   * Set the length of each record
055   * @param conf configuration
056   * @param recordLength the length of a record
057   */
058  public static void setRecordLength(Configuration conf, int recordLength) {
059    conf.setInt(FIXED_RECORD_LENGTH, recordLength);
060  }
061
062  /**
063   * Get record length value
064   * @param conf configuration
065   * @return the record length, zero means none was set
066   */
067  public static int getRecordLength(Configuration conf) {
068    return conf.getInt(FIXED_RECORD_LENGTH, 0);
069  }
070
071  @Override
072  public RecordReader<LongWritable, BytesWritable>
073      createRecordReader(InputSplit split, TaskAttemptContext context)
074      throws IOException, InterruptedException {
075    int recordLength = getRecordLength(context.getConfiguration());
076    if (recordLength <= 0) {
077      throw new IOException("Fixed record length " + recordLength
078          + " is invalid.  It should be set to a value greater than zero");
079    }
080    return new FixedLengthRecordReader(recordLength);
081  }
082
083  @Override
084  protected boolean isSplitable(JobContext context, Path file) {
085    final CompressionCodec codec = 
086        new CompressionCodecFactory(context.getConfiguration()).getCodec(file);
087    return (null == codec);
088  } 
089
090}