How to read a Stream one by one?

Question

The Java Stream.forEach function has the serious limitation that it's impossible for its consumer to throw checked exceptions. As such, I would like to access a Stream's elements one by one.

I want to do something like this:

while(true) {
    Optional<String> optNewString = myStream.findAny();

    if (optNewString.isPresent())
        doStuff(optNewString.get());
    else
        break;
}

However, findAny is a short-circuiting terminal operation. That is, it closes the stream. This code would crash on the second iteration of the while loop. I cannot simply put all elements inside an array, and go over that array one by one, because there are potentially tens of millions of elements.

Please note I am not asking how to throw exceptions from within forEach. This question has already been answered.

Answer 1

To iterate over a stream element-by-element, just call the iterator() method:

Iterator<String> iterator = stream.iterator();
while (iterator.hasNext()) {
    String element = iterator.next();
    // Use element
}

It's not clear to what extent that helps you in terms of checked exceptions, and it's worth noting that it's a terminal operation - once you've used the iterator, you'd need to get a new stream if you want to iterate again - but it does answer the question of how to read a stream one element at a time.