Java 8 streams map, keep nulls as null

Question

I have this piece of code:

public LatLng[] locationDtoListToLatLngArray(List<LocationDto> locationDtoList) {
    return locationDtoList.stream()
            .map(locationDto -> new LatLng(locationDto.getLatitude(), locationDto.getLongitude()))
            .toArray(LatLng[]::new);
}

but is crashing if locationDto is null inside .map

I fixed it doing this:

public LatLng[] locationDtoListToLatLngArray(List<LocationDto> locationDtoList) {
    return locationDtoList.stream()
            .map(locationDto -> locationDto == null ? null : new LatLng(locationDto.getLatitude(), locationDto.getLongitude()))
            .toArray(LatLng[]::new);
}

but I want to know if there is a better approach (without checking if locationDto == null)

Please note that, if locationDto == null, I want to keep the null, so filter is not an option :)

Thanks

EDIT: I know that the problem is accessing a null object, I just want to know is if there is some function like .map(), that do what I need, .mapKeepingNulls(), something like that.

EDIT 2: I ended up doing this:

public LatLng[] locationDtoListToLatLngArray(List<LocationDto> locationDtoList) {
    return locationDtoList.stream()
            .map(this::locationDtoToLatLng)
            .toArray(LatLng[]::new);
}

private LatLng locationDtoToLatLng(LocationDto locationDto) {
    if (locationDto == null) {
        return null;
    }
    return new LatLng(locationDto.getLatitude(), locationDto.getLongitude());
}

The side-question is: why do you have nulls in the first place in a list? (And I don't think there's a cleaner way, aside from wrapping all of this in an Optional, which would be counterproductive IMO). — Tunaki
– Tunaki, Commented Jul 23, 2016 at 21:39
@SotiriosDelimanolis, yes, I'm thinking that may be some function that do what I want.. .mapKeepingNulls() something like this.. I'm new with streams — Matias Elorriaga
– Matias Elorriaga, Commented Jul 23, 2016 at 21:41

Filip Smola · Accepted Answer · 2016-07-23 21:51:55Z

2

The problem is that you are accessing methods of a potentionally null value. If you really don't want the null check there (which I think is a good solution) you can try making a static method in LatLng that will take the LocationDto and return the right instance or null when the supplied LocationDto is null.

Something like this:

public static LatLng getFromLocationDto(LocationDto ldt){
    if(ldt == null)
        return null;

    return new LatLng(ldt.getLatitude(), ldt.getLongitude());
}

But the null check has to be somewhere (unless you can ensure that there will be no null int the locationDtoList).

answered Jul 23, 2016 at 21:51

Filip Smola

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zoom · Accepted Answer · 2016-07-23 21:53:44Z

0

The issue as little to do with Java 8 streams. You are getting an NullPointerException when doing locationDto.getLatitude().

It is totally normal to check for null value. If you were not in a stream, I am almost sure that you would have not disturbed you.

Maybe what you dislike is the fact that you are performing inline conditional operation in a one-liner, in which case I advise you to use an helper function like _createLatLng(LocationDto locationDto) to externalize that process.

answered Jul 23, 2016 at 21:53

zoom

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zakaria amine · Accepted Answer · 2016-07-23 22:01:45Z

0

You can make use of Optional, which is a new class in Java 8 made for this purpose.

// transform locationDtoList to a list of Optional

locationDtoList.stream()
        .filter(Optional::isPresent)
        .map(Optional::get)
        .map(locationDto -> new LatLng(locationDto.getLatitude(),      locationDto.getLongitude()))
        .toArray(LatLng[]::new);

answered Jul 23, 2016 at 22:01

zakaria amine

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