How to create a Simple Factory Pattern with autowi

问题:

I had a controller with 4 very similar methods, calling an API on a remote server to perform different actions on different types of users. What changed between these API calls are just the endpoint and some parameters.

Therefore, these 4 methods all called services with very similar code: they got a token from the server, set the parameters, return the API's response. Since more actions will be added later, I decided to use create a ServiceFactory using the Factory Method pattern and use the Template pattern on the services to avoid code duplication.

My problem is that in order for the factory to autowire the services, it needs to be coupled to them, I have to @Autowire every implementation. Is there a better solution?

Here's the code I have so far:

Rest Controller

@RestController
public class ActionController {
  @Autowired
  private SsoService ssoService;

  // this is the factory
  @Autowired
  private ServiceFactory factory;

  @PostMapping("/action")
  public MyResponse performAction(@RequestBody MyRequest request, HttpServletRequest req) {
    // template code (error treatment not included)
    request.setOperator(ssoService.getOperator(req));
    request.setDate(LocalDateTime.now());
    return serviceFactory.getService(request).do();
  }
}

Service Factory

@Component
public class ServiceFactory {

  @Autowired private ActivateUserService activateUserService;
  @Autowired private Action2UserType2Service anotherService;
  //etc

  public MyService getService(request) {
    if (Action.ACTIVATE.equals(request.getAction()) && UserType.USER.equals(request.getUserType()) {
      return activateUserService;
    }
    // etc
    return anotherService;
  }
}

Service Base, implementing the MyService interface

public abstract class ServiceBase implements MyService {

  @Autowired private ApiService apiService;
  @Autowired private ActionRepository actionRepository;
  @Value("${api.path}") private String path;

  @Override
  public MyResponse do(MyRequest request) {
    String url = path + getEndpoint();
    String token = apiService.getToken();

    Map<String, String> params = getParams(request);
    // adds the common params to the hashmap

    HttpResult result = apiService.post(url, params); 
    if (result.getStatusCode() == 200) {
      // saves the performed action
      actionRepository.save(getAction());
    }
    // extracts the response from the HttpResult
    return response;
  }
}

Service Implementation (there are 4)

@Service
public class ActivateUserService extends ServiceBase {
  @Value("${api.user.activate}")
  private String endpoint;

  @Override
  public String getEndpoint() {
    return endpoint;
  }

  @Override
  public Map<String,String> getParams(MyRequest request) {
    Map<String, String> params = new HashMap<>();
    // adds custom params
    return params;
  }

  @Override
  public Action getAction() {
    return new Action().type(ActionType.ACTIVATED).userType(UserType.USER);
  }
}

回答1:

You can @Autowired a List of MyService, which will create a List of all beans that implement the MyService interface. Then you can add a method to MyService that accepts a MyRequest object and decides if it can handle that request. You can then filter the List of MyService to find the first MyService object that can handle the request.

For example:

public interface MyService {

    public boolean canHandle(MyRequest request);

    // ...existing methods...
}

@Service
public class ActivateUserService extends ServiceBase {

    @Override
    public boolean canHandle(MyRequest request) {
        return Action.ACTIVATE.equals(request.getAction()) && UserType.USER.equals(request.getUserType());
    }

    // ...existing methods...
}

@Component
public class ServiceFactory {

    @Autowired
    private List<MyService> myServices;

    public Optional<MyService> getService(MyRequest request) {
        return myServices.stream()
            .filter(service -> service.canHandle(request))
            .findFirst();
    }
}

Note that the ServiceFactory implementation above uses Java 8+. If it is not possible to Java 8 or higher, you can implement the ServiceFactory class in the following manner:

@Component
public class ServiceFactory {

    @Autowired
    private List<MyService> myServices;

    public Optional<MyService> getService(MyRequest request) {

        for (MyService service: myServices) {
            if (service.canHandle(request)) {
                return Optional.of(service);
            }
        }

        return Optional.empty();
}

For more information on using @Autowired with List, see Autowire reference beans into list by type.

---

The core of this solution is moving the logic of deciding if a MyService implementation can handle a MyRequest from the ServiceFactory (an external client) to the MyService implementation itself.