RxJava - streaming directly to file

import io.reactivex.Observable;

import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Stream;

public class Streaming {

    public static void main(String[] args) throws IOException {
        // create Java 8 stream in try-with-resource
        try(Stream<String> stream = Files.lines(Paths.get("data.txt"))) {

            // convert stream into Observable (no data loaded yet)
            Observable<List<String>> buffer = Observable.fromIterable(stream::iterator)
                    .buffer(2)
                    .filter(s -> true); // do whatever transformations are needed

            // pass reactive stream into writing function (still no data loaded)
            writeToCsv(buffer);
        }
    }

    private static void writeToCsv(Observable<List<String>> buffer) throws IOException {
        FileWriter fw = new FileWriter("out.csv");

        // subscribe to reactive stream -> now do work and write results directly to file!
        buffer.forEach(record -> fw.append("..."));
    }

}