Create and save Sequence files in a foreachPartition function in Spark

Question

I am trying to load a group of files, make some checks on them and later saving them in HDFS. I haven't found a good way to create and save these Sequence files, though. Here is my loader main function

SparkConf sparkConf = new SparkConf().setAppName("writingHDFS")
            .setMaster("local[2]")
            .set("spark.streaming.stopGracefullyOnShutdown", "true");
    JavaSparkContext jsc = new JavaSparkContext(sparkConf);
    //JavaStreamingContext jssc = new JavaStreamingContext(sparkConf, new Duration(5*1000));

    JavaPairRDD<String, PortableDataStream> imageByteRDD = jsc.binaryFiles("file:///home/cloudera/Pictures/cat");
    JavaPairRDD<String, String> imageRDD = jsc.wholeTextFiles("file:///home/cloudera/Pictures/");

    imageRDD.mapToPair(new PairFunction<Tuple2<String,String>, Text, Text>() {

        @Override
        public Tuple2<Text, Text> call(Tuple2<String, String> arg0)
                throws Exception {
            return new Tuple2<Text, Text>(new Text(arg0._1),new Text(arg0._2));
        }

    }).saveAsNewAPIHadoopFile("hdfs://localhost:8020/user/hdfs/sparkling/try.seq", Text.class, Text.class, SequenceFileOutputFormat.class);

It simply loads some images as text files, puts the name of the file as key of the PairRDD and use the native saveAsNewAPIHadoopFile. I would like now to save file by file in ardd.foreach or rdd.foreachPartition` but I cannot find a proper method:

This stackoverflow answer creates a Job for the occasion. It seems to work, but it needs the file inputed as a path, while I already have an RDD made of them
A couple of solution I found create a directory for each file (OutputStream out = fs.create(new Path(dst));) which wouldn't be as much of a problem, if it weren't for the fact that I get an exception for Mkdirs didn't work

EDIT: I may have found a way, but I have a Task not serializable exception:
JavaPairRDD imageByteRDD = jsc.binaryFiles("file:///home/cloudera/Pictures/cat");

    imageByteRDD.foreach(new VoidFunction<Tuple2<String,PortableDataStream>>() {

        @Override
        public void call(Tuple2<String, PortableDataStream> fileTuple) throws Exception {
            Text key = new Text(fileTuple._1());
              BytesWritable value = new BytesWritable( fileTuple._2().toArray());
                 SequenceFile.Writer writer = SequenceFile.createWriter(serializableConfiguration.getConf(), SequenceFile.Writer.file(new Path("/user/hdfs/sparkling/" + key)),
                       SequenceFile.Writer.compression(SequenceFile.CompressionType.RECORD, new BZip2Codec()),
                       SequenceFile.Writer.keyClass(Text.class), SequenceFile.Writer.valueClass(BytesWritable.class));
                    key = new Text("MiaoMiao!");
                    writer.append(key, value);
                 IOUtils.closeStream(writer);


        }
    });

I have tried wrapping the entire function in a Serializable class, but no luck. Help?

Vale · Accepted Answer · 2016-07-04T08:55:20.507

The way I did it was a (pseudocode, I'll try to edit this answer as soon as I get to my office)

rdd.foreachPartition{
    Configuration conf = ConfigurationSingletonClass.getConfiguration();
    etcetera, etcetera...
}

EDIT: got to my office, here is the complete segment of code: the configuration is created inside the rdd.foreachPartition (for each was a little too much). In the iterator there is the file writing itself, to a sequence file format.

 JavaPairRDD<String, PortableDataStream> imageByteRDD = jsc.binaryFiles(SOURCE_PATH);
    if(!imageByteRDD.isEmpty())
        imageByteRDD.foreachPartition(new VoidFunction<Iterator<Tuple2<String,PortableDataStream>>>() {

            @Override
            public void call(
                    Iterator<Tuple2<String, PortableDataStream>> arg0)
                    throws Exception {
                Configuration conf = new Configuration();
                conf.set("fs.defaultFS", HDFS_PATH);
                while(arg0.hasNext()){
                    Tuple2<String,PortableDataStream>fileTuple = arg0.next();
                    Text key = new Text(fileTuple._1());
                    String fileName = key.toString().split(SEP_PATH)[key.toString().split(SEP_PATH).length-1].split(DOT_REGEX)[0];
                    String fileExtension = fileName.split(DOT_REGEX)[fileName.split(DOT_REGEX).length-1];

                      BytesWritable value = new BytesWritable( fileTuple._2().toArray());
                         SequenceFile.Writer writer = SequenceFile.createWriter(
                                 conf, 
                                 SequenceFile.Writer.file(new Path(DEST_PATH + fileName + SEP_KEY + getCurrentTimeStamp()+DOT+fileExtension)),
                               SequenceFile.Writer.compression(SequenceFile.CompressionType.RECORD, new BZip2Codec()),
                               SequenceFile.Writer.keyClass(Text.class), SequenceFile.Writer.valueClass(BytesWritable.class));
                         key = new Text(key.toString().split(SEP_PATH)[key.toString().split(SEP_PATH).length-2] + SEP_KEY + fileName + SEP_KEY + fileExtension);
                            writer.append(key, value);
                         IOUtils.closeStream(writer);

                }
            }
        });

Hope this will help.

Create and save Sequence files in a foreachPartition function in Spark

1 Answers1