Java spring map 无法推断类型变量 R

Question

我找了很久也没找到解决这个问题的方法。在我的 spring 应用程序中，我有一个 BesoinPoseMapper

@FunctionalInterface
@Mapper(uses = BesoinPoseTranslator.class)
public interface BesoinPoseMapper {
    @Mappings({
            @Mapping(target = "nbCapteurs", source = "valeur", qualifiedByName = {"BesoinPoseTranslator", "nbCapteurs"}),
            @Mapping(target = "typologie", source = "typologie", qualifiedByName = {"BesoinPoseTranslator", "typologie"}),
            @Mapping(target = "site", source = "site", qualifiedByName = {"BesoinPoseTranslator", "emplacement"})
    })
    BesoinPoseDTO entityToDTO(BesoinPoseEntity entity);
}

将 BesoinPoseEntity 映射到 BesoinPoseDTO

但是BesoinPoseController中的 map 函数

public class BesoinPoseController {

    @Setter
    @Autowired
    private BesoinPoseRepository besoinPoseRepo;

    @GetMapping()
    public List<BesoinPoseDTO> getBesoinsPose(@RequestParam String range, @RequestParam(required = false) String status){

        return StreamSupport.stream(besoinPoseRepo.findAll().spliterator(), false)
                .map(BesoinPoseMapper::entityToDTO)
                .collect(Collectors.toList());
    }
}

抛出编译错误

                .map(BesoinPoseMapper::entityToDTO);
                ^
  required: Function<? super BesoinPoseEntity,? extends R>
  found: BesoinPose[...]ToDTO
  reason: cannot infer type-variable(s) R
    (argument mismatch; invalid method reference
      cannot find symbol
        symbol:   method entityToDTO(BesoinPoseEntity)
        location: interface BesoinPoseMapper)
  where R,T are type-variables:
    R extends Object declared in method <R>map(Function<? super T,? extends R>)
    T extends Object declared in interface Stream

我尝试使用 lambda 并将类型从可迭代更改为列表和数组，然后返回流，但无济于事，错误仍然存​​在。编译器无法推断 R 类型是 BesoinPoseDTO 。

有办法解决这个问题吗？

谢谢

Answer 1

一旦生成映射器的实现，您需要创建一个 BesoinPoseMapper 实例，换句话说，这是实例的入口点，如下所示:

@Mapper(uses = BesoinPoseTranslator.class)
public interface BesoinPoseMapper {
    BesoinPoseMapper INSTANCE = Mappers.getMapper(BesoinPoseMapper.class);
    //...
}

现在在您的组件中您可以使用:

.map(BesoinPoseMapper.INSTANCE::entityToDTO);

或:

private BesoinPoseMapper besoinPoseMapper = BesoinPoseMapper.INSTANCE;

...

.map(besoinPoseMapper::entityToDTO);

---

Spring

或者因为您使用的是 spring，您可以使用 componentModel = "spring":

@Mapper(uses = BesoinPoseTranslator.class, componentModel = "spring")

然后您可以将映射器作为任何 Spring 组件注入(inject)到您的组件中，例如:

@Autowired
private BesoinPoseMapper besoinPoseMapper;

---

• 3.2. Mapping Composition (experimental)
• 4.2. Using dependency injection