InvalidDefinitionException：无法构造“com.vehicle.datatransferobject.VehicleDTO”的实例

Question

在我在 Spring Boot 中构建的 REST 端点中，我试图将我的 vehicleDTO 传递给我的控制器。但在它到达我的控制器之前，出现了错误。

InvalidDefinitionException：无法构造实例 com.vehicle.datatransferobject.VehicleDTO（没有创作者，默认 构造，存在）：不能从对象值反序列化（没有委托- 或基于属性的创建者）

vehicleDTO

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.myvehicle.EngineType;

@JsonInclude(JsonInclude.Include.NON_NULL)
public class VehicleDTO {

    @JsonIgnore
    private Long id;

    @NotNull(message = "vehiclenumber can not be null!")
    private String vehiclenumber;

    @Min(2)
    @NotNull(message = "Seat count can not be less than 2!")
    private Integer vehicleseatcount;

    @NotNull(message = "Engine Type can not be null!")
    private EngineType enginetype;

    @Max(5)
    private Integer vehiclerating;



    private VehicleDTO(Long id, String vehiclenumber, Integer vehicleseatcount, EngineType enginetype,Integer vehiclerating){
        this.vehiclenumber=vehiclenumber;
        this.vehicleseatcount=vehicleseatcount;
        this.enginetype=enginetype;
        this.vehiclerating=vehiclerating;
        this.id=id;
    }

    public static VehicleDTOBuilder newBuilder()
    {
        return new VehicleDTOBuilder();
    }

    @JsonProperty
    public Long getId() {
        return id;
    }


    public String getvehiclenumber() {
        return vehiclenumber;
    }


    public Integer getvehicleseatcount() {
        return vehicleseatcount;
    }


    public EngineType getEnginetype() {
        return enginetype;
    }



    public Integer getvehiclerating() {
        return vehiclerating;
    }




    public static class VehicleDTOBuilder{

        private Long id;
        private String vehiclenumber;
        private Integer vehicleseatcount;
        private EngineType enginetype;
        private Integer vehiclerating;

        public VehicleDTOBuilder setId(Long id) {
            this.id = id;
            return this;
        }
        public VehicleDTOBuilder setvehiclenumber(String vehiclenumber) {
            this.vehiclenumber = vehiclenumber;
            return this;
        }
        public VehicleDTOBuilder setvehicleseatcount(Integer vehicleseatcount) {
            this.vehicleseatcount = vehicleseatcount;
            return this;
        }
        public VehicleDTOBuilder setEnginetype(EngineType enginetype) {
            this.enginetype = enginetype;
            return this;
        }
        public VehicleDTOBuilder setvehiclerating(Integer vehiclerating) {
            this.vehiclerating = vehiclerating;
            return this;
        }


        public VehicleDTO createVehicleDTO()
        {
            return new VehicleDTO(id, vehiclenumber, vehicleseatcount, enginetype,vehiclerating);
        }

    }

}

我的 DTO 有一个名为 EngineType 的枚举类型

public enum EngineType {
    ELECTRIC, DIESEL
}

我的控制器是这样的

@PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public VehicleDTO addvehicle(@Valid @RequestBody VehicleDTO vehicleDTO) 
    {
        VehicleDO vehicleDO = Mapper.VehicleDO(vehicleDTO);
        return Mapper.makeVehicleDTO(Service.addvehicle(vehicleDO));
    }

Answer 1

这个例外：

InvalidDefinitionException：无法构造实例 com.vehicle.datatransferobject.VehicleDTO（无创作者，如默认 构造，存在）：不能从对象值反序列化（没有委托- 或基于属性的创建者）

意味着 Jackson 没有找到实例化 VehicleDTO 的方法，即默认构造函数（无 arg 构造函数）或 JsonCreator。
当您使用构建器模式时，您将配置 VehicleDTO 类以使 Jackson 使用 VehicleDTOBuilder 实例化 VehicleDTO，例如：

@JsonDeserialize(builder = VehicleDTO.VehicleDTOBuilder.class)
public class VehicleDTO {
      ...         
}

并使用JsonPOJOBuilder 将您的构建器注释为：

@JsonPOJOBuilder(buildMethodName = "createVehicleDTO", withPrefix = "set")
public static class VehicleDTOBuilder{ 
   ...
}

根据 javadoc，JsonPOJOBuilder 是：

用于配置 Builder 类的详细信息：其实例是 用作反序列化 POJO 值的构建器，而不是 POJO 使用构造函数或工厂方法实例化。请注意，这 注解不用于定义 POJO 的 Builder 类： 相反，这是由 JsonDeserialize.builder() 的属性确定的 JsonDeserialize。

Answer 2

当我在用于连接到 API（用于消费或提供响应）的 POJO 类上同时使用 Lombok 的 @Builder 和 @Data 注释时遇到此错误

我删除了@Builder 注释，然后它工作正常

Answer 3

就我而言：

InvalidDefinitionException: Cannot construct instance of com.vehicle.datatransferobject.VehicleDTO (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

对于上述异常，我只写了Default Constructor，它实例化了类并解决了问题。

默认构造函数：

public VehicleDTO() {
        super();
        // TODO Auto-generated constructor stub
    }

Answer 4

除了davidxxx的回答。我用过龙目岛。就我而言，它看起来像这样：

@Data
@JsonDeserialize(builder = SomeClass.SomeClassBuilder.class)
@Builder(builderClassName = "SomeClassBuilder")
public class SomeClass {
    // ...

    @JsonPOJOBuilder(withPrefix = "")
    public static class SomeClassBuilder {
    }
}