如何在 map reduce 程序中解析 PDF 文件？

Question

我想在我的 hadoop 2.2.0 程序中解析 PDF 文件，我找到了this，按照它所说的，直到现在，我有这三个类：

1. PDFWordCount: 包含 map 和 reduce 函数的主类。 （就像native hadoop wordcount 示例，但我使用了PDFInputFormat 类而不是TextInputFormat。

2. PDFRecordReader extends RecordReader<LongWritable, Text>:这是这里的主要工作。特别是我把我的initialize 函数放在这里以获得更多说明。

   public void initialize(InputSplit genericSplit, TaskAttemptContext context)
         throws IOException, InterruptedException {
         System.out.println("initialize");
         System.out.println(genericSplit.toString());
       FileSplit split = (FileSplit) genericSplit;
       System.out.println("filesplit convertion has been done");
       final Path file = split.getPath();
       Configuration conf = context.getConfiguration();
       conf.getInt("mapred.linerecordreader.maxlength", Integer.MAX_VALUE);
       FileSystem fs = file.getFileSystem(conf);
       System.out.println("fs has been opened");
       start = split.getStart();
       end = start + split.getLength();
       System.out.println("going to open split");
       FSDataInputStream filein = fs.open(split.getPath());
       System.out.println("going to load pdf");
       PDDocument pd = PDDocument.load(filein);
       System.out.println("pdf has been loaded");
       PDFTextStripper stripper = new PDFTextStripper();
       in =
       new LineReader(new ByteArrayInputStream(stripper.getText(pd).getBytes(
           "UTF-8")));
       start = 0;
       this.pos = start;
       System.out.println("init has finished");
     }
   

   （您可以查看我的system.out.printlns 进行调试。 此方法无法将genericSplit 转换为FileSplit。我在控制台中看到的最后一件事是：

   hdfs://localhost:9000/in:0+9396432
   

   这是genericSplit.toString()

3. PDFInputFormat extends FileInputFormat<LongWritable, Text>: 只是在createRecordReader 方法中创建new PDFRecordReader。

我想知道我的错误是什么？

我需要额外的课程吗？

Answer 1

阅读 PDF 并不难，您需要扩展类 FileInputFormat 以及 RecordReader。 FileInputClass 不应该能够拆分 PDF 文件，因为它们是二进制文件。

public class PDFInputFormat extends FileInputFormat<Text, Text> {

  @Override
  public RecordReader<Text, Text> createRecordReader(InputSplit split,
    TaskAttemptContext context) throws IOException, InterruptedException {
      return new PDFLineRecordReader();
  }

  // Do not allow to ever split PDF files, even if larger than HDFS block size
  @Override
  protected boolean isSplitable(JobContext context, Path filename) {
    return false;
  }

}

RecordReader 然后自行执行阅读（我正在使用 PDFBox 阅读 PDF）。

public class PDFLineRecordReader extends RecordReader<Text, Text> {

private Text key = new Text();
private Text value = new Text();
private int currentLine = 0;
private List<String> lines = null;

private PDDocument doc = null;
private PDFTextStripper textStripper = null;

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

    FileSplit fileSplit = (FileSplit) split;
    final Path file = fileSplit.getPath();

    Configuration conf = context.getConfiguration();
    FileSystem fs = file.getFileSystem(conf);
    FSDataInputStream filein = fs.open(fileSplit.getPath());

    if (filein != null) {

        doc = PDDocument.load(filein);

        // Konnte das PDF gelesen werden?
        if (doc != null) {
            textStripper = new PDFTextStripper();
            String text = textStripper.getText(doc);

            lines = Arrays.asList(text.split(System.lineSeparator()));
            currentLine = 0;

        }

    }
}

    // False ends the reading process
@Override
public boolean nextKeyValue() throws IOException, InterruptedException {

    if (key == null) {
        key = new Text();
    }

    if (value == null) {
        value = new Text();
    }

    if (currentLine < lines.size()) {
        String line = lines.get(currentLine);

        key.set(line);

        value.set("");
        currentLine++;

        return true;
    } else {

        // All lines are read? -> end
        key = null;
        value = null;
        return false;
    }
}

@Override
public Text getCurrentKey() throws IOException, InterruptedException {
    return key;
}

@Override
public Text getCurrentValue() throws IOException, InterruptedException {
    return value;
}

@Override
public float getProgress() throws IOException, InterruptedException {
    return (100.0f / lines.size() * currentLine) / 100.0f;
}

@Override
public void close() throws IOException {

    // If done close the doc
    if (doc != null) {
        doc.close();
    }

}

希望这会有所帮助！

Answer 2

package com.sidd.hadoop.practice.pdf;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
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.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import com.sidd.hadoop.practice.input.pdf.PdfFileInputFormat;
import com.sidd.hadoop.practice.output.pdf.PdfFileOutputFormat;

public class ReadPdfFile {

    public static class MyMapper extends
            Mapper<LongWritable, Text, LongWritable, Text> {
        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
//          context.progress();
            context.write(key, value);
        }
    }

    public static class MyReducer extends
            Reducer<LongWritable, Text, LongWritable, Text> {
        public void reduce(LongWritable key, Iterable<Text> values,
                           Context context) throws IOException, InterruptedException {
            if (values.iterator().hasNext()) {
                context.write(key, values.iterator().next());
            } else {
                context.write(key, new Text(""));
            }
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();

        Job job = new Job(conf, "Read Pdf");
        job.setJarByClass(ReadPdfFile.class);

        job.setMapperClass(MyMapper.class);
        job.setReducerClass(MyReducer.class);
        job.setOutputKeyClass(LongWritable.class);
        job.setOutputValueClass(Text.class);

        job.setInputFormatClass(PdfFileInputFormat.class);
        job.setOutputFormatClass(PdfFileOutputFormat.class);

        removeDir(args[1], conf);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

    public static void removeDir(String path, Configuration conf) throws IOException {
        Path output_path = new Path(path);
        FileSystem fs = FileSystem.get(conf);

        if (fs.exists(output_path)) {
            fs.delete(output_path, true);
        }
    }   

}