java - 如何处理通用接口(interface)实现并避免@SuppressWarnings？

Question

我试图对不同的服务实现进行通用处理，但我不断收到“由于原始类型而未经检查的调用”错误。

我尝试了几种实现，但不太明白这里的问题是什么。

我有以下模型:

public abstract class Fruit {

  public List<String> vitamins;
  public String originCountry;

  // getters and setters omitted
}

具体实现如下:

public class Kiwi extends Fruit {
}

public class Pineapple extends Fruit {
}

我有以下界面:

public interface FruitCheckService<T extends Fruit> {

  List<String> compareVitaminsFromDifferentCountries(T firstFruit, T secondFruit);

  Class<T> getImplementation();
}

上面给出的 2 个模型的实现:

@Service
public class KiwiCheckServiceImpl implements FruitCheckService<Kiwi> {

  @Override
  public List<String> compareVitaminsFromDifferentCountries(Kiwi firstFruit, Kiwi secondFruit) {
    // some implementation
    return new ArrayList<>();
  }

  @Override
  public Class<Kiwi> getImplementation() {
    return Kiwi.class;
  }
}

还有菠萝:

@Service
public class PineappleCheckServiceImpl implements FruitCheckService<Pineapple> {

  @Override
  public List<String> compareVitaminsFromDifferentCountries(Pineapple firstFruit, Pineapple secondFruit) {
    // some implementation
    return new ArrayList<>();
  }

  @Override
  public Class<Pineapple> getImplementation() {
    return Pineapple.class;
  }
}

我有以下类，它使用不同的 bean 进行操作:

@Service
public class FruitServices {

  private Map<Class, FruitCheckService> beansMap;

  @Autowired
  public FruitServices(List<FruitCheckService> fruitCheckServices) {

    beansMap = new HashMap<>();

    fruitCheckServices
      .forEach(
        fruitCheckService -> {
          Class implementation = fruitCheckService.getImplementation();
          beansMap.put(implementation, fruitCheckService);
        }
      );
  }


  public FruitCheckService getFruitCheckService(Class clazz) {
    return beansMap.get(clazz);
  }
}

最后，这是我调用的服务:

@Component
public class BusinessService {

  @Autowired
  private FruitServices fruitServices;

  public void compareVitamins(Fruit one, Fruit two) {

    Class<? extends Fruit> aClass = one.getClass();

    FruitCheckService fruitCheckService = fruitServices.getFruitCheckService(aClass);

    List<String> result = fruitCheckService.compareVitaminsFromDifferentCountries(one, two);
  }
}

如何正确使用fruitCheckService而不收到“作为原始类型'exercise2.service.FruitCheckService'的成员对'compareVitaminsFromDifferentCountries(T, T)'的未经检查的调用”？

Answer 1

问题是您在服务定义中使用原始类型Class。要解决此问题，您可以使用 bounded wildcard type ?，例如:

class FruitServices {

  private Map<Class<? extends Fruit>, FruitCheckService<? extends Fruit>> beansMap;


  public FruitServices(List<FruitCheckService<? extends Fruit>> fruitCheckServices) {

    beansMap = new HashMap<>();

    fruitCheckServices
      .forEach(
        fruitCheckService -> {
          Class<? extends Fruit> implementation = fruitCheckService.getImplementation();
          beansMap.put(implementation, fruitCheckService);
        }
      );
  }

  public FruitCheckService<? extends Fruit> getFruitCheckService(Class<? extends Fruit> clazz) {
    return beansMap.get(clazz);
  }
}

对于 BusinessService 类，事情会变得更加棘手。首先，有必要使 compareVitamins 成为一个通用方法，以确保两种水果属于同一类型。但即便如此，我也不相信您可以避免 getFruitCheckService 结果中的未经检查的强制转换，因为，由于 FruitServices 必须处理不同类型水果的服务，您getFruitCheckService 的返回值不能有精确的类型参数。

class BusinessService {

    private FruitServices fruitServices;

    public <T extends Fruit> void compareVitamins(T one, T two) {

        @SuppressWarnings("unchecked")
        FruitCheckService<T> fruitCheckService = 
            (FruitCheckService<T>) fruitServices.getFruitCheckService(one.getClass());

        List<String> result = fruitCheckService.compareVitaminsFromDifferentCountries(one, two);
    }
}