Spring 3 - Dynamic Autowiring at runtime based on another object attribute

Question

I am working on a Spring 3.1 MVC application and for one of my scenarios, I had to write two implementations of a DAO. I would like to know how to autowire this in a service

Answer 1

My solution would be as follows:

a method isResponsibleFor in the VehicleDao interface:

interface VehicleDao {
    public boolean isResponsibleFor(Vehicle vehicle);
}

example implementation:

@Repository
class CarDAO implements VehicleDAO {
    public boolean isResponsibleFor(Vehicle vehicle) {
        return "CAR".equals(vehicle.getType());
    }
}

then autowire a list of all VehicleDao-implementations in the VehicleService:

public class VehicleServiceImpl implements VehicleService {

    @Autowired
    private List vehicleDaos;

    private VehicleDao daoForVehicle(Vehicle vehicle) {
         foreach(VehicleDao vehicleDao : vehicleDaos) {
              if(vehicleDao.isResponsibleFor(vehicle) {
                   return vehicleDao;
              }
         }

         throw new UnsupportedOperationException("unsupported vehicleType");
    }

    @Transactional
    public void save(Vehicle vehicle) {
         daoForVehicle(vehicle).save(vehicle);
    }
}

This has the advantage that you don't need to modify the service when you are adding a new vehicleType at a later time - you just need to add a new VehicleDao-implementation.