Java8 Stream of files, how to control the closing of files?

Question

Suppose I have a Java8 Stream and that I use that stream to map and such, how can I control the closing of the FileReader

Answer 1

So, if you only have non-binary files you could use something like this:

List fileNames = Arrays.asList(
            "C:\\Users\\wowse\\hallo.txt",
            "C:\\Users\\wowse\\bye.txt");

fileNames.stream()
            .map(Paths::get)
            .filter(Files::exists)
            .flatMap(path -> {
                try {
                    return Files.lines(path);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            })
            .forEach(System.out::println);

If you have binary files which you can hold in memory you can try following approach.

fileNames.stream()
            .map(Paths::get)
            .filter(Files::exists)
            .map(path -> {
                try {
                    return Files.readAllBytes(path);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                return null;
            })
            .filter(Objects::nonNull)
            .map(String::new)
            .forEach(System.out::println);

Other than that I think you would have to use some wrapper class, where I could suggest Map.Entry or the Pair from javafx so you don't have to use any external libraries.