Filter and map a java stream at the same time

Question

I have a list of strings, each of which is represents a date. I'd like to map this list into a list of DateTime objects; however, if any of the strings are invalid (throws an exception) I'd like to log an error but not add it to the final List. Is there a way to do both the filtering and mapping at the same time?

This is what I currently have:

List<String> dateStrs = ...;
dateStrs.stream().filter(s -> {
    try {
        dateTimeFormatter.parseDateTime(s);
        return true;
    } catch (Exception e) {
        log.error("Illegal format");
        return false;
    }
}.map(s -> {
    return dateTimeFormatter.parseDateTime(s);
}.collect(...);

Is there any way to do this so that I don't have to parseDateTime twice for each element?

Thanks

Answer 1

To my opinion, it would be more idiomatically correct to use flatMap here:

dateStrs.stream().flatMap(s -> {
    try {
        return Stream.of(dateTimeFormatter.parseDateTime(s));
    } catch (Exception e) {
        return Stream.empty();
    }
}).collect(...);

Here you can do everything in single operation.