Java中MapStruct的DTO与实体逆向映射难题咨询

在Java项目中使用MapStruct库进行DTO与实体映射时，遇到了职责拆分和逆向映射的挑战。核心目标是拆分不同DTO和映射类的映射职责：

• UserDto包含ContactDto，ContactDto包含AddressDto
• User实体为扁平结构，整合了所有嵌套DTO中的字段
• 期望UserMapper仅负责映射UserDto的字段，ContactMapper、AddressMapper同理各自处理对应DTO的映射逻辑

正向映射代码 #

ContactMapper #

@Mapper(componentModel = "spring",
        unmappedTargetPolicy = ReportingPolicy.IGNORE,
        uses = AddressMapper.class
)
public abstract class ContactMapper {
    public static final ContactMapper MAPPER = Mappers.getMapper(ContactMapper.class);

    @Mapping(source = "user", target = "address")
    public abstract ContactDto toDto(User user);

}

UserMapper #

@Mapper(componentModel = "spring",
        uses = ContactMapper.class,
        unmappedTargetPolicy = ReportingPolicy.IGNORE
)
public abstract class UserMapper {
    public static final UserMapper MAPPER = Mappers.getMapper(UserMapper.class);

    @Mapping(source = "user", target = "contact")
    public abstract UserDto toDto(User user);

}

自动生成的UserMapperImpl #

@Generated(
    value = "org.mapstruct.ap.MappingProcessor",
    date = "2024-01-24T16:45:56+0100",
    comments = "version: 1.5.5.Final, compiler: IncrementalProcessingEnvironment from gradle-language-java-8.5.jar, environment: Java 17.0.10 (Amazon.com Inc.)"
)
@Component
public class UserMapperImpl extends UserMapper {

    @Autowired
    private ContactMapper contactMapper;

    @Override
    public UserDto toDto(User user) {
        if ( user == null ) {
            return null;
        }

        UserDto.UserDtoBuilder userDto = UserDto.builder();

        userDto.contact( contactMapper.toDto( user ) );
        userDto.firstName( user.getFirstName() );
        userDto.lastName( user.getLastName() );

        return userDto.build();
    }
}

逆向映射的困境 #

目前在实现*逆向映射（DTO转实体）*时遇到目标值缺失的问题，不确定如何推进。不想通过@AfterMapping或@BeforeMapping增加不必要的复杂度，更希望避免以下这种冗长的手动映射写法：

@Mapping(target = "email", source = "email")
@Mapping(target = "phoneNumber", source = "phoneNumber")
@Mapping(source = "addressDto.street", target = "street")
@Mapping(source = "addressDto.city", target = "city")
public abstract User toEntity(ContactDto contactDto);

这种方式在大型项目中会生成大量样板代码，实用性极低。正在寻找一种无需过多手动配置、具备可扩展性的解决方案，希望得到针对这类MapStruct问题的建议或替代实现方法。

内容的提问来源于stack exchange，提问作者Kathelan