Hadoop: the Mapper didn't read files from multiple input paths - dictionary

Question

The Mapper didn't manage to read a file from multiple directories. Could anyone help?
I need to read one file in each mapper. I've added multiple input paths and implemented the custom WholeFileInputFormat, WholeFileRecordReader. In the map method, I don't need the input key. I make sure that each map can read a whole file.
Command line: hadoop jar AutoProduce.jar Autoproduce /input_a /input_b /output
I specified two input path----1.input_a; 2.input_b;
Run method snippets:
Job job = new Job(getConf());
job.setInputFormatClass(WholeFileInputFormat.class);
FileInputFormat.setInputPaths(job, new Path(args[0]), new Path(args[1]));
FileOutputFormat.setOutputPath(job, new Path(args[2]));
map method snippets:
public void map(NullWritable key, BytesWritable value, Context context){
FileSplit fileSplit = (FileSplit) context.getInputSplit();
System.out.println("Directory :" + fileSplit.getPath().toString());
......
}
Custom WholeFileInputFormat:
class WholeFileInputFormat extends FileInputFormat<NullWritable, BytesWritable> {
#Override
protected boolean isSplitable(JobContext context, Path file) {
return false;
}
#Override
public RecordReader<NullWritable, BytesWritable> createRecordReader(
InputSplit split, TaskAttemptContext context) throws IOException,
InterruptedException {
WholeFileRecordReader reader = new WholeFileRecordReader();
reader.initialize(split, context);
return reader;
}
}
Custom WholeFileRecordReader:
class WholeFileRecordReader extends RecordReader<NullWritable, BytesWritable> {
private FileSplit fileSplit;
private Configuration conf;
private BytesWritable value = new BytesWritable();
private boolean processed = false;
#Override
public void initialize(InputSplit split, TaskAttemptContext context)
throws IOException, InterruptedException {
this.fileSplit = (FileSplit) split;
this.conf = context.getConfiguration();
}
#Override
public boolean nextKeyValue() throws IOException, InterruptedException {
if (!processed) {
byte[] contents = new byte[(int) fileSplit.getLength()];
Path file = fileSplit.getPath();
FileSystem fs = file.getFileSystem(conf);
FSDataInputStream in = null;
try {
in = fs.open(file);
IOUtils.readFully(in, contents, 0, contents.length);
value.set(contents, 0, contents.length);
} finally {
IOUtils.closeStream(in);
}
processed = true;
return true;
}
return false;
}
#Override
public NullWritable getCurrentKey() throws IOException,InterruptedException {
return NullWritable.get();
}
#Override
public BytesWritable getCurrentValue() throws IOException,InterruptedException {
return value;
}
#Override
public float getProgress() throws IOException {
return processed ? 1.0f : 0.0f;
}
#Override
public void close() throws IOException {
// do nothing
}
}
PROBLEM:
After setting two input paths, all map tasks read files from only one directory..
Thanks in advance.

Answer 1

You'll have to use MultipleInputs instead of FileInputFormat in the driver. So your code should be as:
MultipleInputs.addInputPath(job, new Path(args[0]), <Input_Format_Class_1>);
MultipleInputs.addInputPath(job, new Path(args[1]), <Input_Format_Class_2>);
.
.
.
MultipleInputs.addInputPath(job, new Path(args[N-1]), <Input_Format_Class_N>);
So if you want to use WholeFileInputFormat for the first input path and TextInputFormat for the second input path, you'll have to use it the following way:
MultipleInputs.addInputPath(job, new Path(args[0]), WholeFileInputFormat.class);
MultipleInputs.addInputPath(job, new Path(args[1]), TextInputFormat.class);
Hope this works for you!