Accumulate a Java Stream and only then process it

Question

I had a document that looked like the following:

data.txt

100, \"some text\"
101, \"more text\"
102, \"even more text\"

I processed

Answer 1

This is a job for java.util.Scanner. With the upcoming Java 9, you would write:

List<MyClass> result;
try(Scanner s=new Scanner(Paths.get("data.txt"))) {
    result = s.findAll("(\\d{1,3}),\\s*\"([^\"]*)\"")
                //MyClass(int id, String text)
    .map(m -> new MyClass(Integer.parseInt(m.group(1)), m.group(2))) 
    .collect(Collectors.toList());
}
result.forEach(System.out::println);

but since the Stream producing findAll does not exist under Java 8, we’ll need a helper method:

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

Replacing findAll with this helper method, we get

List<MyClass> result;
try(Scanner s=new Scanner(Paths.get("data.txt"))) {

    result = matches(s, "(\\d{1,3}),\\s*\"([^\"]*)\"")
               // MyClass(int id, String text)
    .map(m -> new MyClass(Integer.parseInt(m.group(1)), m.group(2)))
    .collect(Collectors.toList());
}