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Apache Hadoop MapReduce Streaming
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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  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 org.apache.hadoop.streaming;

import java.io.EOFException;
import java.io.IOException;

import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.InputFormat;
import org.apache.hadoop.mapred.InputSplit;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.RecordReader;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.mapred.SequenceFileInputFormat;
import org.apache.hadoop.mapred.TextInputFormat;

/**
 * An {@link InputFormat} that tries to deduce the types of the input files
 * automatically. It can currently handle text and sequence files.
 */
public class AutoInputFormat extends FileInputFormat {

  private TextInputFormat textInputFormat = new TextInputFormat();

  private SequenceFileInputFormat seqFileInputFormat = 
    new SequenceFileInputFormat();

  public void configure(JobConf job) {
    textInputFormat.configure(job);
    // SequenceFileInputFormat has no configure() method
  }

  public RecordReader getRecordReader(InputSplit split, JobConf job,
    Reporter reporter) throws IOException {
    FileSplit fileSplit = (FileSplit) split;
    FileSystem fs = FileSystem.get(fileSplit.getPath().toUri(), job);
    FSDataInputStream is = fs.open(fileSplit.getPath());
    byte[] header = new byte[3];
    RecordReader reader = null;
    try {
      is.readFully(header);
    } catch (EOFException eof) {
      reader = textInputFormat.getRecordReader(split, job, reporter);
    } finally {
      is.close();
    }
    if (header[0] == 'S' && header[1] == 'E' && header[2] == 'Q') {
      reader = seqFileInputFormat.getRecordReader(split, job, reporter);
    } else {
      reader = textInputFormat.getRecordReader(split, job, reporter);
    }
    return reader;
  }

}