Using prototype in Spring singleton service

I wanted to use a Spring bean, with private fields in order to build an object. Previously the builder class was really as an example of the builder pattern implemented. It was able to build the required object based on the parameters, defined for the builder.

Later on, after the requirement changed, the builder had to use other services in order to get detailed information for the build process. In this case you have the following possibilities:

• define all services as parameter of the build process, and use them when needed.
  I did not choose this option, as it would not have resulted a clear interface for the builder. The dependent services are mandatory for the build process, but the builder can not force to define them in its interface. So the client has to set up the builder correctly before using it. It would have resulted such a restriction, what I did not want to build into my system.
• Implement the builder as a Spring singleton bean. In this case the singleton must not have a state, so it is not possible to define the build parameters as field of the bean. It would make the implementation less readable, while the parameters must have been passed to the private methods several times.

So I chose to concert my builder class into a Spring prototype bean. The necessary parameters must be set by the client, but the necessary services are injected with CDI by the container.

The result looked like this:

@Service(value = "logicBuilderService")
@Scope("prototype")
public final class LogicBuilderService {

 @Autowired
 private DeviceDAO deviceDao;

 @Autowired
 private SupportedDeviceDao supportedDeviceDao;

 // contains eagerly initialized device and channel collection
 @Setter
 private Gateway gateway;

 @Setter
 private LogicRequest request;

 public Logic build() {
  Logic logic = createNewLogic();
  addTrigger(logic);
  addActions(logic);

  return logic;
 }
....

At the client side, you need to use an Objectfactory, in order to get a new instance of the service. Whenever you need a new, clean instance of the builder, you get it from the Spring framework, without the properties set.

 @Autowired
 private ObjectFactory<LogicBuilderService> prototypeFactory;

 private LogicBuilderService getNewLogicBuilderServiceInstance(Gateway gateway, LogicRequest request) {
  LogicBuilderService logicBuilder = prototypeFactory.getObject();
  logicBuilder.setGateway(gateway);
  logicBuilder.setRequest(request);

  return logicBuilder;
 }

In order to use the LogicBuilderService in a unit test, you need to mock the ObjectFactory, so it returns a new instance of the builder for all calls.

@Mock
 private ObjectFactory<LogicBuilderService> prototypeFactory;

 @InjectMocks
 private LogicRestService logicRestService;

 @Before
 public void setup() {
  when(prototypeFactory.getObject()).thenReturn(new LogicBuilderService());
 }