/**
* Constructs a new {@link FeedMessage.Builder} that can be used to build a new GTFS-realtime feed
* message. The {@link FeedHeader} will already be filled in as a {@link
* Incrementality#FULL_DATASET} and the timestamp of the feed will be set to NOW. This is the
* minimal requirement for an empty feed so the feed could be returned 'as-is' at this point.
*
* @return a new feed message builder with a header already populated
*/
public static FeedMessage.Builder createFeedMessageBuilder() {
long now = System.currentTimeMillis();
FeedHeader.Builder header = FeedHeader.newBuilder();
header.setTimestamp(now / 1000);
header.setIncrementality(Incrementality.FULL_DATASET);
header.setGtfsRealtimeVersion(GtfsRealtimeConstants.VERSION);
FeedMessage.Builder feedMessageBuilder = FeedMessage.newBuilder();
feedMessageBuilder.setHeader(header);
return feedMessageBuilder;
}
/**
* This method downloads the latest vehicle data, processes each vehicle in turn, and create a
* GTFS-realtime feed of trip updates and vehicle positions as a result.
*/
private void refreshVehicles() throws IOException, JSONException {
/** We download the vehicle details as an array of JSON objects. */
JSONArray vehicleArray = downloadVehicleDetails();
/**
* The FeedMessage.Builder is what we will use to build up our GTFS-realtime feeds. We create a
* feed for both trip updates and vehicle positions.
*/
FeedMessage.Builder tripUpdates = GtfsRealtimeLibrary.createFeedMessageBuilder();
FeedMessage.Builder vehiclePositions = GtfsRealtimeLibrary.createFeedMessageBuilder();
/** We iterate over every JSON vehicle object. */
for (int i = 0; i < vehicleArray.length(); ++i) {
JSONObject obj = vehicleArray.getJSONObject(i);
String trainNumber = obj.getString("trainno");
String route = obj.getString("dest");
String stopId = obj.getString("nextstop");
double lat = obj.getDouble("lat");
double lon = obj.getDouble("lon");
int delay = obj.getInt("late");
/**
* We construct a TripDescriptor and VehicleDescriptor, which will be used in both trip
* updates and vehicle positions to identify the trip and vehicle. Ideally, we would have a
* trip id to use for the trip descriptor, but the SEPTA api doesn't include it, so we settle
* for a route id instead.
*/
TripDescriptor.Builder tripDescriptor = TripDescriptor.newBuilder();
tripDescriptor.setRouteId(route);
VehicleDescriptor.Builder vehicleDescriptor = VehicleDescriptor.newBuilder();
vehicleDescriptor.setId(trainNumber);
/**
* To construct our TripUpdate, we create a stop-time arrival event for the next stop for the
* vehicle, with the specified arrival delay. We add the stop-time update to a TripUpdate
* builder, along with the trip and vehicle descriptors.
*/
StopTimeEvent.Builder arrival = StopTimeEvent.newBuilder();
arrival.setDelay(delay * 60);
StopTimeUpdate.Builder stopTimeUpdate = StopTimeUpdate.newBuilder();
stopTimeUpdate.setArrival(arrival);
stopTimeUpdate.setStopId(stopId);
TripUpdate.Builder tripUpdate = TripUpdate.newBuilder();
tripUpdate.addStopTimeUpdate(stopTimeUpdate);
tripUpdate.setTrip(tripDescriptor);
tripUpdate.setVehicle(vehicleDescriptor);
/**
* Create a new feed entity to wrap the trip update and add it to the GTFS-realtime trip
* updates feed.
*/
FeedEntity.Builder tripUpdateEntity = FeedEntity.newBuilder();
tripUpdateEntity.setId(trainNumber);
tripUpdateEntity.setTripUpdate(tripUpdate);
tripUpdates.addEntity(tripUpdateEntity);
/**
* To construct our VehiclePosition, we create a position for the vehicle. We add the position
* to a VehiclePosition builder, along with the trip and vehicle descriptors.
*/
Position.Builder position = Position.newBuilder();
position.setLatitude((float) lat);
position.setLongitude((float) lon);
VehiclePosition.Builder vehiclePosition = VehiclePosition.newBuilder();
vehiclePosition.setPosition(position);
vehiclePosition.setTrip(tripDescriptor);
vehiclePosition.setVehicle(vehicleDescriptor);
/**
* Create a new feed entity to wrap the vehicle position and add it to the GTFS-realtime
* vehicle positions feed.
*/
FeedEntity.Builder vehiclePositionEntity = FeedEntity.newBuilder();
vehiclePositionEntity.setId(trainNumber);
vehiclePositionEntity.setVehicle(vehiclePosition);
vehiclePositions.addEntity(vehiclePositionEntity);
}
/** Build out the final GTFS-realtime feed messagse and save them. */
_gtfsRealtimeProvider.setTripUpdates(tripUpdates.build());
_gtfsRealtimeProvider.setVehiclePositions(vehiclePositions.build());
_log.info("vehicles extracted: " + tripUpdates.getEntityCount());
}