I get the null value of deviceService while running the following code?

Question

This is the code of controller class and while running the deviceService returns null value. the deviceService should return some value in controller from service class.

 @ManagedBean
    @ViewScoped
    public class DeviceController implements Serializable {

        private Device device;
        private List<Device> deviceList;

        @ManagedProperty("#{deviceService}")
        public DeviceService deviceService;

    /**
         * @return the deviceService
         */
        public DeviceService getDeviceService() {
            return deviceService;
        }

        /**
         * @param deviceService the deviceService to set
         */
        public void setDeviceService(DeviceService deviceService) {
            this.deviceService = deviceService;

        }

and this is deviceService class code

@Service("deviceService")
@Transactional(readOnly = true)
public class DeviceService {

    @Autowired
    IDeviceDao iDevice;

    @Transactional(readOnly = false)
    public void addDevice(Device device) {
        iDevice.addDevice(device);
    }

    public List<Device> getDeviceList() {
        return iDevice.getDeviceList();
    }

    @Transactional(readOnly = false)
    public void deleteDevice(Device device) {
        iDevice.deleteDevice(device);
    }
}