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Writing a Custom InputFormatΒΆ

You can use a custom Java InputFormat together with a Python RecordReader: the RecordReader supplied by the InputFormat will be overridden by the Python one.

Consider the following simple modification of Hadoop’s built-in TextInputFormat:

package net.sourceforge.pydoop.mapred;

import java.io.*;

import org.apache.hadoop.fs.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;


public class TextInputFormat extends FileInputFormat<LongWritable, Text>
    implements JobConfigurable {

    private Boolean will_split;

    public void configure(JobConf conf) {
      will_split = conf.getBoolean("pydoop.input.issplitable", true);
    }

    protected boolean isSplitable(FileSystem fs, Path file) {
      return will_split;
    }

    public RecordReader<LongWritable, Text> getRecordReader(
        InputSplit genericSplit, JobConf job, Reporter reporter
        )
      throws IOException {
      reporter.setStatus(genericSplit.toString());
      return new LineRecordReader(job, (FileSplit) genericSplit);
    }
}

With respect to the default one, this InputFormat adds a configurable boolean parameter (pydoop.input.issplitable) that, if set to false, makes input files non-splitable (i.e., you can’t get more input splits than the number of input files).

For details on how to compile the above code into a jar and use it with pipes, see examples/input_format in the Pydoop distribution root. You can run the input_format example with:

cd examples/input_format
./run