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Pdf Input Format implementation for Hadoop Mapreduce

In my opinion Hadoop is not a cooked tool or framework with readymade features, but it is an efficient framework which allows a lot of customizations  based on our usecases. It is our choice to modify it. By modification, I am not meaning about the modification of the architecture or working, but the modification of its functionality and features.

By default hadoop accepts text files.  But in practical scenarios, our input files may not be text files. It can be pdf, ppt, pst, image or anything. So we need to make hadoop compatible with this various types of input formats.

Here I am explaining about the creation of a custom input format for hadoop. I am explain the code for implementing pdf reader logic inside hadoop. Similarly  you can create any custom reader of your choice. The fundamental is same.

A simple pdf to text conversion program using java is  explained in my previous post PDF to Text. This is a simple pdf parser which converts the text content of the pdf only. If you want more features, you can modify it accordingly. My intention here is to explain about the creation of a custom input format reader for hadoop.

For doing this logic, we need to write or modify two classes.

One is we need a similar class like the default TextInputFormat.class for pdf. We can call it as PdfInputFormat.class.

Second one is we need a similar class like the default LineRecordReader for handling pdf. We can call it as PdfRecordReader.class

If you examine the source code of hadoop, you can see that the default TextInputFormat class is extended from a parent class called FileInputFormat.

So in our case, we can also create a PdfinputFormat class extending the FileInputFormat class.

This will contain a method called createRecordReader which it got from the parent class.

We are calling our custom PdfRecordReader class from this createRecordReader method.

The code for PdfInputFormat is given below.

package com.amal.pdf;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
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.FileInputFormat;

public class PdfInputFormat extends FileInputFormat {

	@Override
	public RecordReader createRecordReader(
			InputSplit split, TaskAttemptContext context) throws IOException,
			InterruptedException {

		return new PdfRecordReader();
	}

}

The PdfRecordReader is a custom class created by us extending the RecordReader.

This mainly contains  five methods which is inherited from the parent RecordReader class.

Initialize(), nextKeyValue(),getCurrentKey(),getCurrentValue(), getProgress(), close().

The logic I am using is explained below.

We are applying our pdf parsing logic in this method. This method will get the input split and we parses the input split using our pdf parser logic. The output of the pdf parser will be a text which will be stored in a variable. Then we splits the text into multiple lines by using ‘/n’ as the splitter and we will store this lines in  an array.

We need to send this as a key-value pair. So I am planning to send line number as the key and each line as value. So the logic for checking  getting from the array, setting it as key and value , checking for the completion condition etc are written in the code.

The PdfRecordReader  code is written below.

package com.amal.pdf;

import java.io.IOException;
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.io.LongWritable;
import org.apache.hadoop.io.Text;
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.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.util.PDFTextStripper;

public class PdfRecordReader extends RecordReader {

	private String[] lines = null;
	private LongWritable key = null;
	private Text value = null;

	@Override
	public void initialize(InputSplit genericSplit, TaskAttemptContext context)
			throws IOException, InterruptedException {

		FileSplit split = (FileSplit) genericSplit;
		Configuration job = context.getConfiguration();
		final Path file = split.getPath();

		/*
		 * The below code contains the logic for opening the file and seek to
		 * the start of the split. Here we are applying the Pdf Parsing logic
		 */

		FileSystem fs = file.getFileSystem(job);
		FSDataInputStream fileIn = fs.open(split.getPath());
		PDDocument pdf = null;
		String parsedText = null;
		PDFTextStripper stripper;
		pdf = PDDocument.load(fileIn);
		stripper = new PDFTextStripper();
		parsedText = stripper.getText(pdf);
		this.lines = parsedText.split("\n");

	}

	@Override
	public boolean nextKeyValue() throws IOException, InterruptedException {

		if (key == null) {
			key = new LongWritable();
			key.set(1);
			value = new Text();
			value.set(lines[0]);
		} else {
			int temp = (int) key.get();
			if (temp < (lines.length - 1)) {
				int count = (int) key.get();
				value = new Text();
				value.set(lines[count]);
				count = count + 1;
				key = new LongWritable(count);
			} else {
				return false;
			}

		}
		if (key == null || value == null) {
			return false;
		} else {
			return true;
		}
	}

	@Override
	public LongWritable getCurrentKey() throws IOException,
			InterruptedException {

		return key;
	}

	@Override
	public Text getCurrentValue() throws IOException, InterruptedException {

		return value;
	}

	@Override
	public float getProgress() throws IOException, InterruptedException {

		return 0;
	}

	@Override
	public void close() throws IOException {

	}

}

For using this in a program, you need to specify this in the driver class. We need to set our custom input format class in the “InputFormatClass” property of our mapreduce program.
For getting a complete picture, I am associating this  with the basic word count mapreduce program.

Driver Class

package com.amal.pdf;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.GenericOptionsParser;

public class PdfInputDriver {

	public static void main(String[] args) throws IOException,
			InterruptedException, ClassNotFoundException {
		Configuration conf = new Configuration();
		GenericOptionsParser parser = new GenericOptionsParser(conf, args);
		args = parser.getRemainingArgs();
		Job job = new Job(conf, "Pdfwordcount");
		job.setJarByClass(PdfInputDriver.class);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(LongWritable.class);
		job.setInputFormatClass(PdfInputFormat.class);
		job.setOutputFormatClass(TextOutputFormat.class);
		FileInputFormat.setInputPaths(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));
		job.setMapperClass(WordCountMapper.class);
		job.setReducerClass(WordCountReducer.class);

		System.out.println(job.waitForCompletion(true));
	}
}

Mapper Class

package com.amal.pdf;

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.TaskAttemptContext;

public class WordCountMapper extends
		Mapper {
	private Text word = new Text();
	private final static LongWritable one = new LongWritable(1);

	protected void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
		String line = value.toString();
		StringTokenizer tokenizer = new StringTokenizer(line);
		while (tokenizer.hasMoreTokens()) {
			word.set(tokenizer.nextToken());
			context.progress();
			context.write(word, one);
		}
	}
}

Reducer Class

package com.amal.pdf;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class WordCountReducer extends
		Reducer {
	protected void reduce(Text key, Iterable values,
			Context context) throws IOException, InterruptedException {
		int sum = 0;
		for (LongWritable value : values) {
			sum += value.get();

		}
		context.write(key, new LongWritable(sum));
	}
}

In a similar way, you can write any custom input format as you wish. 🙂 🙂

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