Java streams, wait for Google distance matrix to return result

Question

I have a list of vehicles that I need to calculate the total fuel used per vehicle. I am using Java streams to loop through the list, get a vehicle, calculate its distance using the Google distance matrix api, use the distance to calculate fuel usage and return a response. I have noticed that the program just hangs most likely it could be that the stream does not wait for the Matrix api to return a response before it moves to the next item, I say this because I have put system.out.println calls in the Matrix method and some messages do not get printed.

The code that is suppose to calculate total fuel usage

vehicles.stream().map(vehicles ->
                calculateTotalFuelBeingUsedByAllVehicles(vehicle, getDistanceBetweenOriginsAndDestination(
                        new LatLng(vehicle.getOrigin().getLatitude(), vehicle.getOrigin().getLatitude()), new LatLng(vehicle.getDestination().getLatitude(), vehicles.getDestination().getLatitude()))))
                .collect(Collectors.toList());

    public static double getDistanceBetweenOriginsAndDestination(LatLng origin, LatLng destination){
        //Gets printed
        System.out.println("Calculating distance");
        GeoApiContext context = new GeoApiContext.Builder()
                .apiKey(GOOGLE_MAPS_API_KEY)
                .build();
        DistanceMatrixApiRequest distanceMatrixApiRequest = DistanceMatrixApi.newRequest(context)
                .mode(TravelMode.DRIVING)
                .trafficModel(TrafficModel.BEST_GUESS)
                .departureTime(Instant.now().atZone(ZoneOffset.UTC).toInstant())
                .destinations(destination)
                .origins(origin);
        try {

            long distance =  Arrays.stream(distanceMatrixApiRequest.await().rows)
                    .flatMap(distanceMatrixRow -> Arrays.stream(distanceMatrixRow.elements))
                    .mapToLong(distanceMatrixElement -> distanceMatrixElement.distance.inMeters)
                    .sum();

            //Never gets printed
            System.out.println("Calculated distance: "+distance);
            return distance;

        } catch (ApiException | InterruptedException | IOException e) {
            //Never gets printed
            System.out.println("Error encountered when calculating distance");
            e.printStackTrace();
        }
        return 0;
    }

In the getDistanceBetweenOriginsAndDestination the System.out.println("Calculating distance") gets printed and the rest are not.

So, it's getting stuck at `distanceMatrixApiRequest.await()`? — Andy Turner, May 29 '19 at 07:10
@AndyTurner I think so but naturally this method is suppose to return a response after sometime but in this case its not. — Astonio, May 29 '19 at 07:11
You have a typo at the creation of `LatLng`, you send latitude instead of longitude. It may be Google doesn't respond you or takes a lot of time to respond, because it is impossible to calculate a route between these points. Just a suggestion. — DDovzhenko, May 29 '19 at 07:15
@DmytroDovzhenko is right, check this line: `new LatLng(vehicle.getOrigin().getLatitude(), vehicle.getOrigin().getLatitude())`, there is `getLatitude()` two times... Might be the issue here. — deHaar, May 29 '19 at 07:19
@DmytroDovzhenko wow, Thanks alot, it has worked, please make this an answer so I can mark it. — Astonio, May 29 '19 at 07:24

score 1 · Accepted Answer · answered May 29 '19 at 07:32

1

You have a typo at the creation of LatLng, you send latitude instead of longitude. It may be Google doesn't respond you or takes a lot of time to respond, because it is impossible to calculate a route between these points.

answered May 29 '19 at 07:32

DDovzhenko

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Java streams, wait for Google distance matrix to return result

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