Java spring map无法推断类型变量R

Question

我已经搜索了很多时间，但找不到解决此问题的方法。在我的春季申请中，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());
    }
}

引发编译错误

                .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，然后再返回到流，但无济于事，错误仍然存​​在。编译器无法推断出 R 类型是 BesoinPoseDTO。

有没有办法解决这个问题？

谢谢

Answer 1

您需要创建一个BesoinPoseMapper 的实例，换句话说，一旦您的映射器的实现生成如下：

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

现在您可以在您的组件中使用：

.map(BesoinPoseMapper.INSTANCE::entityToDTO);

或：

private BesoinPoseMapper besoinPoseMapper = BesoinPoseMapper.INSTANCE;

...

.map(besoinPoseMapper::entityToDTO);

---

春天

或者因为你使用的是spring你可以使用componentModel = "spring":

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

然后您可以将映射器作为任何弹簧组件注入您的组件中，例如：

@Autowired
private BesoinPoseMapper besoinPoseMapper;

---

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