How to manage BDM in REST API extensions

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.SerializationFeature


class CarManagement implements RestApiController {

    private static final Logger LOGGER = LoggerFactory.getLogger(CarManagement.class)

    // Use a shared instance for performance reason (see https://github.com/FasterXML/jackson-docs/wiki/Presentation:-Jackson-Performance)
    private static final ObjectMapper jsonBuilder = new ObjectMapper()
    static {
        // needed to serialize BDM object because of the Bonita lazy loading mechanism
        jsonBuilder.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS)
    }

    @Override
    RestApiResponse doHandle(HttpServletRequest request, RestApiResponseBuilder responseBuilder, RestAPIContext context) {
        // To retrieve query parameters use the request.getParameter(..) method.
        // Be careful, parameter values are always returned as String values

        // Retrieve p parameter
        def p = request.getParameter "p"
        if (p == null) {
            return buildResponse(responseBuilder, HttpServletResponse.SC_BAD_REQUEST,"""{"error" : "the parameter p is missing"}""")
        }

        // Retrieve c parameter
        def c = request.getParameter "c"
        if (c == null) {
            return buildResponse(responseBuilder, HttpServletResponse.SC_BAD_REQUEST,"""{"error" : "the parameter c is missing"}""")
        }

        // use APIClient to retrieve the CarDAO class:
        def carDAO = context.apiClient.getDAO(CarDAO.class)

        def currentModel = "DeLorean"
        // Fetch the cars that match the search criteria:
        List<Car> cars = carDAO.findByModel(currentModel, p as int, c as int)

        // Prepare the Json result:
        def result = [ "model" : currentModel, "number of cars" : cars.size(), "cars" : cars ]

        return buildResponse(responseBuilder, HttpServletResponse.SC_OK, jsonBuilder.writeValueAsString(result))
    }

/***********************
 ***** SERIALIZER ******
 ***********************/

import com.fasterxml.jackson.core.JsonGenerator
import com.fasterxml.jackson.databind.JsonSerializer
import com.fasterxml.jackson.databind.SerializerProvider

class CarSerializer extends JsonSerializer<Car>{

	@Override
	public void serialize(Car car, JsonGenerator jgen, SerializerProvider provider)throws IOException, JsonProcessingException {
		jgen.writeStartObject()

		jgen.writeNumberField("carID", car.getPersistenceId())
		jgen.writeStringField("model", car.getModel())
		jgen.writeNumberField("buildYear", car.getBuildYear())
		jgen.writeStringField("color", car.getColor())
		jgen.writeStringField("wheel1Request", getWheelRequest(car.getPersistenceId(), 1))
		jgen.writeStringField("wheel2Request", getWheelRequest(car.getPersistenceId(), 2))
		jgen.writeStringField("wheel3Request", getWheelRequest(car.getPersistenceId(), 3))
		jgen.writeStringField("wheel4Request", getWheelRequest(car.getPersistenceId(), 4))

		jgen.writeEndObject()
	}

	private String getWheelRequest(Long carID, Integer wheelNum) {
		return String.format('../API/extension/wheel?p=0&c=10&carID=%s&wheelNum=%s', carID, wheelNum)
	}

}

/***********************
 ******* MAPPER ********
 ***********************/

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.SerializationFeature
import com.fasterxml.jackson.databind.module.SimpleModule

class CarObjectMapper extends ObjectMapper {
	public CarObjectMapper () {
	    SimpleModule module = new SimpleModule()
	    module.addSerializer(Car.class, new CarSerializer())
	    registerModule(module)
    }
}

/***********************
 ******** INDEX ********
 ***********************/

class CarIndex implements RestApiController {

    private static final Logger LOGGER = LoggerFactory.getLogger(CarIndex.class)
    private static final CarObjectMapper CAR_MAPPER = new CarObjectMapper()

    @Override
    RestApiResponse doHandle(HttpServletRequest request, RestApiResponseBuilder responseBuilder, RestAPIContext context) {
        def p = request.getParameter "p"
        def c = request.getParameter "c"

		def carDAO = context.apiClient.getDAO(CarDAO.class)
		int startIndex = (p as Integer)*(c as Integer)
		int endIndex = c as Integer
		List<Car> cars = carDAO.find(startIndex, endIndex)

		def result = CAR_MAPPER.writeValueAsString(cars)

        return buildResponse(responseBuilder, HttpServletResponse.SC_OK, result)
    }

    RestApiResponse buildResponse(RestApiResponseBuilder responseBuilder, int httpStatus, Serializable body) {
        return responseBuilder.with {
            withResponseStatus(httpStatus)
            withResponse(body)
            build()
        }
    }

}