Java 8 stream emitting a stream

Question

I have the following file format:

Text1
+ continuation of Text1
+ more continuation of Text1 
Text2
+ continuation of Text2
+ more continuation of Text2
+ ev         


        

Answer 1

Assuming that you run this sequentially only and really want to use streams:

 List<String> result = Files.lines(Paths.get("YourPath"))
            .collect(() -> new ArrayList<>(), (list, line) -> {
                int listSize = list.size();
                if (line.startsWith("+ ")) {
                    list.set(listSize - 1, list.get(listSize - 1) + line.substring(2));
                } else {
                    list.add(line);
                }
            }, (left, right) -> {
                throw new RuntimeException("Not for parallel processing");
            });

Answer 2

In Java 9, you could use

static final Pattern LINE_WITH_CONTINUATION = Pattern.compile("(\\V|\\R\\+)+");

…

try(Scanner s = new Scanner(file)) {
    s.findAll(LINE_WITH_CONTINUATION)
        .map(m -> m.group().replaceAll("\\R\\+", ""))
        .forEach(System.out::println);
}

Since Java 8 lacks the Scanner.findAll(Pattern) method, you may add a custom implementation of the operation as a work-around

public static Stream<MatchResult> findAll(Scanner s, Pattern pattern) {
    return StreamSupport.stream(new Spliterators.AbstractSpliterator<MatchResult>(
            1000, Spliterator.ORDERED|Spliterator.NONNULL) {
        public boolean tryAdvance(Consumer<? super MatchResult> action) {
            if(s.findWithinHorizon(pattern, 0)!=null) {
                action.accept(s.match());
                return true;
            }
            else return false;
        }
    }, false);
}

which can be used like

try(Scanner s = new Scanner(file)) {
    findAll(s, LINE_WITH_CONTINUATION)
        .map(m -> m.group().replaceAll("\\R\\+", ""))
        .forEach(System.out::println);
}

which will make the future migration easy.