MapStruct中BeanMapping忽略默认配置对子类属性不生效问题咨询

问题出在MapStruct的@SubclassMapping自动生成的子类映射方法不会继承父类映射方法上的@BeanMapping(ignoreByDefault = true)配置，默认会自动匹配子类的同名属性，导致你设置的忽略默认映射规则对子类属性无效。

以下是两种无需逐个显式映射子类的优化解决方法：

方案一：全局配置忽略默认映射 #

通过@MapperConfig定义全局映射规则，让所有映射方法默认启用ignoreByDefault，无需在每个方法上重复配置：

@MapperConfig(beanMapping = @BeanMapping(ignoreByDefault = true))
public interface UserMapperConfig {
}

修改UserMapper，引入该全局配置：

@Mapper(
    subclassExhaustiveStrategy = SubclassExhaustiveStrategy.RUNTIME_EXCEPTION,
    config = UserMapperConfig.class
)
public abstract class UserMapper {

    @Mapping(source = "id", target = "id")
    @Mapping(source = "firstName", target = "firstName")
    @Mapping(source = "lastName", target = "lastName")
    @SubclassMapping(source = Employee.class, target = EmployeeDTO.class)
    @SubclassMapping(source = Contractor.class, target = ContractorDTO.class)
    public abstract UserDTO map(User user);
}

这样生成的子类映射方法（employeeToEmployeeDTO、contractorToContractorDTO）会自动遵循全局规则，仅映射你显式指定的id、firstName、lastName属性，子类独有的designation、contractingCompanyName等属性不会被自动映射。

方案二：让子类映射方法继承父类配置 #

如果不想使用全局配置，可以显式定义子类映射方法，通过@InheritConfiguration复用父类的映射规则：

@Mapper(subclassExhaustiveStrategy = SubclassExhaustiveStrategy.RUNTIME_EXCEPTION)
public abstract class UserMapper {

    @BeanMapping(ignoreByDefault = true)
    @Mapping(source = "id", target = "id")
    @Mapping(source = "firstName", target = "firstName")
    @Mapping(source = "lastName", target = "lastName")
    @SubclassMapping(source = Employee.class, target = EmployeeDTO.class)
    @SubclassMapping(source = Contractor.class, target = ContractorDTO.class)
    public abstract UserDTO map(User user);

    @InheritConfiguration(name = "map")
    protected abstract EmployeeDTO employeeToEmployeeDTO(Employee employee);

    @InheritConfiguration(name = "map")
    protected abstract ContractorDTO contractorToContractorDTO(Contractor contractor);
}

@InheritConfiguration会继承父类map方法的@BeanMapping和@Mapping配置，确保子类映射方法也启用ignoreByDefault，且仅映射指定属性，无需重复编写映射规则。

验证效果：生成的子类映射方法中，只会保留id、firstName、lastName的映射代码，不会自动生成子类独有属性的映射逻辑。

内容的提问来源于stack exchange，提问作者Kartik