How to make scanner strings into a Stream in Java?

Question

In Java8, how can I form a Stream of String out of the scanner read results?

InputStream is = A.class.getResourceAsStream("data.txt");
Scanner scanner = new Scanner(new BufferedInputStream(is), "UTF-8");
while (scanner.hasNextLine()) {
    System.out.println(scanner.nextLine());
}

That is turn a scanner into a stream which I would like to iterate using forEach.

What exactly do you want to do? It is impossible to have a stream of strings in the way you want. — The Guy with The Hat, Apr 13 '15 at 17:50
@BoristheSpider `Scanner implements Iterator`. So the answer is the same. (Make a `Spliterator` and use `StreamSupport`.) — Radiodef, Apr 13 '15 at 18:05

Boris the Spider · Accepted Answer · 2015-04-13T18:09:05.993

15

You are going about this all wrong, no Scanner is required:

try (final InputStream is = A.class.getResourceAsStream("data.txt");
        final Reader r = new InputStreamReader(is, StandardCharsets.UTF_8);
        final BufferedReader br = new BufferedReader(r);
        final Stream<String> lines = br.lines()) {

}

If you really want to use a Scanner then it implements Iterator so you can just do:

public Stream<String> streamScanner(final Scanner scanner) {
    final Spliterator<String> splt = Spliterators.spliterator(scanner, Long.MAX_VALUE, Spliterator.ORDERED | Spliterator.NONNULL);
    return StreamSupport.stream(splt, false)
            .onClose(scanner::close);
}

P.S. you also don't seem to be closing resources. always close an InputStream.

edited Apr 13 '15 at 18:09

answered Apr 13 '15 at 17:50

Boris the Spider

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Is `lines` instantiated in a lazy way or `br.lines` reads all the lines? – Stephan Rozinsky Apr 13 '15 at 17:56
@StephanRozinsky it's a `Stream`. What do you think? – Boris the Spider Apr 13 '15 at 17:56
I think it is similar to answer with `Files.lines` below and the entire file can be read only if I use `forEach` on it. I'm learning these things so not confident yet. – Stephan Rozinsky Apr 13 '15 at 18:02
@StephanRozinsky correct. In Java 8 every `Stream` is lazy. – Boris the Spider Apr 13 '15 at 18:03
Is the declaration of each object separately (InputStream, Reader, BufferedReader) to ensure try-with-resources cleans up each? – charles-allen Jun 24 '19 at 13:48
@AjahnCharles nope. Just for clarity because `new BufferedReader(new InputStreamReader(A.class.getResourceAsStream("data.txt"), StandardCharsets.UTF_8)).br.lines()` just isn't very readable. `close()` is required to close dependant resources. – Boris the Spider Jun 24 '19 at 13:57

Bubletan · Answer 2 · 2015-04-13T17:54:09.947

3

You don't have to create a Scanner at all. Just the the resource as a URL.

URL url = A.class.getResource("data.txt");
Files.lines(Paths.get(url.getPath())).forEach(line -> {});

edited Apr 13 '15 at 17:54

answered Apr 13 '15 at 17:53

Bubletan

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If it's on the class path this won't work. – Boris the Spider Apr 13 '15 at 17:53
@BoristheSpider Oh yeah, I guess it won't work if it's a JAR. – Bubletan Apr 13 '15 at 17:57
Am I right that `Files.readAllBytes(Paths.get(...))` reads entire file while Files.lines establishes a stream such the without iterating it I will not read the entire file - so lazyness will work ? – Stephan Rozinsky Apr 13 '15 at 18:00
@StephanRozinsky According to documentation, yes. – Bubletan Apr 13 '15 at 18:05
`Files.lines` uses a `BufferedReader`, so it doesn't read the actual file line-by-line. – Bubletan Apr 13 '15 at 18:13

How to make scanner strings into a Stream in Java?

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