项目转换DTO使用总结，常用技巧

概要

mapstruct在当前轻量级框架开发中的重点使用，@Named注解使用示例，@AfterMapping与@BeforeMapping注解的详细常见用法，在转换DTO时，与过去常用的beanUtil转换有高性能的转换优势，编译期自动生成的mapper实现类能够更加优雅的来实现各种隐式类型转换，以实现快速而又敏捷的开发，告别臃肿的手动get、set与类型的强转

引入

当前core-service引入版本如下

<properties>
    <mapstruct.version>1.2.0.Final</mapstruct.version>
</properties>
<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-jdk8</artifactId>
    <version>${mapstruct.version}</version>
</dependency>
<dependency>
    <groupId>org.mapstruct</groupId>
    <artifactId>mapstruct-processor</artifactId>
    <version>${mapstruct.version}</version>
</dependency>

基本使用

• 使用@Mapper注解，声明映射器，可以是接口，或者抽象类
• 使用@Mapping注解，实现灵活的字段映射，定制映射的规则

注入方式

• 工厂方式

@Mapper
public interface ItemMapper {
    //使用工厂方法获取Mapper实例
    ItemMapper INSTANCE = Mappers.getMapper(ItemMapper.class);
    ItemDTO toDTO(Item item);
}

• 依赖注入方式

@Mapper(componentModel = "spring")
public interface ItemMapper {
    ItemDTO toDTO(Item item);
}

简单映射

代码可以自动生成的Mapper接口，可以自动转换相同属性的字段，无需其他声明。

@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface AwardMapper extends BaseMapper<AwardDTO, Award> {

}

需要注意的是：再不写任何转换代码的情况下，如果实体类中配置了其他关联的一对多或一对一的实体，DTO如果同样需要转换的话，就需要保证属性名一致才能正常转换。

自动类型转换

对于基础数据类型会进行自动隐式的转换如int、long、String，Integer、Long等；

//生成的实现类代码可以看出来
@Component
public class AssemblerImpl implements Assembler {
    @Override
    public ProductDTO toDTO(Product product) {
        if ( product == null ) {
            return null;
        }
        ProductDTO productDTO = new ProductDTO();
        if ( product.getProductId() != null ) {
            //String自动转int
            productDTO.setProductId( Integer.parseInt( product.getProductId() ) );
        }
        if ( product.getPrice() != null ) {
            //Long转String
            productDTO.setPrice( String.valueOf( product.getPrice() ) );
        }
        return productDTO;
    }
}

指定格式转换

查看mapping注解可以看到

@Retention(RetentionPolicy.CLASS)
@Target({ElementType.METHOD})
public @interface Mapping {
    String target();

    String source() default "";

    String dateFormat() default "";

    String numberFormat() default "";
    
    ...
}

dateFormat与numberFormat即可用来进行转换操作

• dateFormat用于日期格式转换

@Mapper(componentModel = "spring")
public interface Demo4Assembler {
    @Mapping(target = "saleTime", dateFormat = "yyyy-MM-dd HH:mm:ss")  //Date转换成String
    @Mapping(target = "validTime", dateFormat = "yyyy-MM-dd HH:mm")    //String转换成Date
    ProductDTO toDTO(Product product);
}

• 日期格式转换可以直接在DTO中注解形式转换，比mapper更为便捷

	// 活动开始时间
	@JsonFormat(pattern = "yyyy/MM/dd HH:mm:ss",timezone="GMT+8")
	private Timestamp startTime;
	
	// 活动结束时间
	@JsonFormat(pattern = "yyyy/MM/dd HH:mm:ss",timezone="GMT+8")
	private Timestamp endTime;

• numberFormat用于数字格式转换【不常用】

   private String price;
   private Integer stock;
	@Mapper(componentModel = "spring")
	public interface Demo3Assembler {
    @Mapping(target = "price", numberFormat = "#.00元") 
    @Mapping(target = "stock", numberFormat = "#个") 
    ProductDTO toDTO(Product product);
}

不同参数映射

• 基本不同属性名转换，需要使用@Mappings注解进行指定转换，参数为数组，支持多个字段转换

@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface DrawRecordDetailMapper extends BaseMapper<DrawRecordDetailDTO, DrawRecord> {
    @Override
    @Mappings({
            @Mapping(target = "chanceId", source = "participationChanceId")
    })
    DrawRecordDetailDTO toDto(DrawRecord entity);

} 

• 对象属性提取和普通属性装载对象中

//将entity中activity实体中name属性装载至DrawRecordDetailDTO中activityName属性上
@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface DrawRecordDetailMapper extends BaseMapper<DrawRecordDetailDTO, DrawRecord> {

    @Override
    @Mappings({
            @Mapping(target = "activityName", source = "activity.name")
    })
    DrawRecordDetailDTO toDto(DrawRecord entity);   
}

//将entity中活动规则属性，转换至ActivityDetailDTO中activityRule对象中
	@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
	public interface ActivityDetailMapper extends BaseMapper<ActivityDetailDTO, Activity> {
	    @Override
	    @Mappings({
	            @Mapping(target = "activityRule.voteOverlapAvailable", source = "voteOverlapAvailable"),
	            @Mapping(target = "activityRule.voteMultipleOnceAvailable", source = 		                                    "voteMultipleOnceAvailable")
	    })
    ActivityDetailDTO toDto(Activity entity);
}    

自定义转换器

• 基础映射方式，mapper接口中直接引入即可（对数据接口要求高）

一个自定义映射器可以定义多个映射方法，匹配时，是以方法的入参和出参进行匹配的

如果绑定的映射中，存在多个相同的入参和出参方法，将会报错

使用样例：将list中多个code在映射时，转换为String用逗号隔开

定义映射器：

@Component
public class MediaServiceFormater {
    public String format(List<String> serviceCodeList) {
        return String.join(",", serviceCode);
    }
}

mapper接口绑定映射器 【uses = {MediaServiceFormater.class}】

@Mapper(componentModel = "spring", uses = {MediaServiceFormater.class,unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface MediaDetailMapper extends BaseMapper<MediaDetailDTO, Media> {

}

• 基于named注解实现【常用】

映射器中使用注解来定义转换方法，使用时，具体属性绑定方法；

定义映射器：

@Component
public class MapStructConverterUtil {
    private static final Logger log = LoggerFactory.getLogger(MapStructConverterUtil.class);

    public MapStructConverterUtil() {
    }

    @Named("getNormalImage")
    public String getNormalImage(String images) {
        if (StringUtils.isEmpty(images)) {
            return null;
        } else {
            try {
                if (images.contains("normal")) {
                    JSONObject imageJson = JSON.parseObject(images);
                    JSONObject mapJson = imageJson.getJSONObject("map");
                    JSONArray normalJson = mapJson.getJSONArray("normal");
                    Integer index = normalJson.getInteger(0);
                    JSONObject object = imageJson.getJSONArray("list").getJSONObject(index);
                    return object.getString("fileUrl");
                }
            } catch (Exception var7) {
                log.error("normal图片解析出错，原images = [{}]", images);
            }

            return null;
        }
    }
  }

使用时绑定映射器：【uses = {MapStructConverterUtil.class}】

@Mapper(componentModel = "spring", uses = {MapStructConverterUtil.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface ActivityUserDetailMapper extends BaseMapper<ActivityUserDetailDTO, Activity> {

    @Override
    @Mappings({
            @Mapping(target = "img1", source = "images", qualifiedByName = "getNormalImage"),
            @Mapping(target = "img2", source = "images", qualifiedByName = "getBgImage"),
            @Mapping(target = "img3", source = "images", qualifiedByName = "getPosterImage")
    })
    ActivityUserDetailDTO toDto(Activity entity);

}

• Map映射

mapStruct还支持map集合的转换，可以对map进行隐式转换，支持对Key与value进行隐式转换

例如：日期转字符串，字符串转日期；同样支持@name注解转换形式，或使用qualifiedBy指定一个转换类（类中默认使用相同入参出参来匹配）

@Mapper(componentModel = "spring", uses = {ConverterUtil.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface SourceTargetMapper {
   @MapMapping(keyQualifiedByName = "getValue", valueDateFormat = "dd.MM.yyyy")
   Map<String, String> longDateMapToStringStringMap(Map<Long, Date> source);
}

复杂映射实现

多个字段映射到一个字段，单个字段快速特殊处理

• 自定义字段表达式映射
  • 单个字段特殊转换处理

@Mapper(componentModel = "spring", unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface GroupDetailOrderMapper extends BaseMapper<GroupDetailOrderDTO, GroupDetailOrder> {

    @Override
    @Mappings({
            @Mapping(target = "userName", expression = "java(entity.getUserName() == null ? \"\" : new String(java.util.Base64.getDecoder().decode(entity.getUserName()), java.nio.charset.StandardCharsets.UTF_8))")
    })
    GroupDetailOrderDTO toDto(GroupDetailOrder entity);
}

• 多个字段处理为一个字段

@Mapper(componentModel = "spring", imports = DecimalUtils.class) 
public interface Demo16Assembler {
    @Mapping(target = "price", expression = "java(product.getPrice1() + product.getPrice2())") 
    @Mapping(target = "price2", expression = "java(DecimalUtils.add(product.getPrice1(), product.getPrice2()))") 
    ProductDTO toDTO(Product product);
}

• 前后置处理实现复杂映射

使用@BeforeMapping与@AfterMapping注解来实现，需要定义默认方法在mapper接口中【java8后支持】

使用前注意：

​ 在调用上下文上的映射方法之前/之后，不执行空检查参数。调用方需要确保在这种情况下不传递null；

@Mapper(componentModel = “spring”, uses = {MapStructConverterUtil.class, MediaConverterUtil.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface MediaDetailMapper extends BaseMapper<MediaDetailDTO, Media> {

 	//前置执行
    @BeforeMapping 
    default MediaDetailDTO setMediaName(Media media) {
        MediaDetailDTO mediaDetailDTO = new MediaDetailDTO();
        mediaDetailDTO.setName("默认名称");
        return mediaDetailDTO;
    }
    
    @Override
    @Mappings({
            @Mapping(target = "img1", source = "images", qualifiedByName = "getNormalImage"),
            @Mapping(target = "img2", source = "images", qualifiedByName = "getBgImage"),
            @Mapping(target = "img3", source = "images", qualifiedByName = "getPosterImage"),
            @Mapping(target = "cp", source = "contentProviderId", qualifiedByName = "getCP"),
            @Mapping(target = "audioTrack", source = "audioDescription")
    })
    MediaDetailDTO toDto(Media media);

	 //后置执行
    @AfterMapping
    default void setMediaType(@MappingTarget MediaDetailDTO mediaDetailDTO, Media media) {
        Integer type = media.getType();
        Integer contentType = media.getContentType();
        String contentTyp = String.format("%02d", contentType);
        mediaDetailDTO.setMediaType(type + contentTyp);
    }
}

隐式映射实现

利用继承关系，继承mapper自动生成的实现类，来重写增强

此转换方式，同样可以实现在dto转换后后置执行，实体真正实现类中代码简洁也较为优雅

需要注意的是，一定要先实现父类转换方法拿到结果后在进行后续增强转换

super.toDto(entity)
实现样例如下：

//实现类引入方式使用@Resource注解引入
 @Autowired
 @Resource(name = "activityDetailMapperImplPlus")
 private ActivityDetailMapper activityDetailMapper;

@Component("activityDetailMapperImplPlus")
@RequiredArgsConstructor
public class ActivityDetailMapperImplPlus extends ActivityDetailMapperImpl {

    private final VoteTargetRepository voteTargetRepository;

    @Override
    public ActivityDetailDTO toDto(Activity entity) {
        ActivityDetailDTO activityDetailDTO = super.toDto(entity);
        
        Long activityDetailDTOId = activityDetailDTO.getId();
        Integer type = activityDetailDTO.getType();
        boolean vote = LocalActConstant.ACT_TYPE_VOTE == type;
        if (vote) {
            Optional<List<VoteTarget>> voteOp = this.voteTargetRepository.findByActivityIdAndStatus(activityDetailDTOId, 1);
            if (voteOp.isPresent()) {
                List<VoteTarget> voteTargets = voteOp.get();
                //累积投票
                activityDetailDTO.setTotalVoteNum(voteTargets.stream()
                        .filter(voteTarget -> voteTarget.getCurrentNumber() != null)
                        .mapToInt(VoteTarget::getCurrentNumber).sum());
            }
        }
        return activityDetailDTO;
    }
}

隐式转换扩展

如果实体类中，关联了其他一对多或多对多的引用类型，JPA在mapper层自动转换后，又需要对引用对象增加出参或出参数据结构转换时，这时候利用转换生成是实现类继承强化后，再绑定到mapper中即可。这样就无需在接口实现层进行循环处理

使用样例如下：

MarketingActivityDetailDTO中有 private List registrationEvents;

需要在BaseRegistrationEventDTO对象中增加出参

//报名人数
private Long totalRegister;
接口侧转换使用的MarketingActivityDetailMapper接口如下:引用必须要包含RegistrationEventSimpleMapperImplPlus.class

uses = {MapStructConverterUtil.class, TemplateParamValueMapper1.class, RegistrationEventSimpleMapperImplPlus.class}

@Mapper(componentModel = "spring", uses = {MapStructConverterUtil.class, TemplateParamValueMapper1.class, RegistrationEventSimpleMapperImplPlus.class}, unmappedTargetPolicy = ReportingPolicy.IGNORE)
public interface MarketingActivityDetailMapper extends BaseMapper<MarketingActivityDetailDTO, MarketingActivity> {

    @Override
    @Mappings({
            @Mapping(target = "img1", source = "images", qualifiedByName = "getNormalImage"),
            @Mapping(target = "img2", source = "images", qualifiedByName = "getBgImage"),
            @Mapping(target = "img3", source = "images", qualifiedByName = "getPosterImage")
    })
    MarketingActivityDetailDTO toDto(MarketingActivity entity);
}

RegistationEventSimpleMapper如下

@Component("registrationEventSimpleMapperImplPlus")
@RequiredArgsConstructor
public class RegistrationEventSimpleMapperImplPlus extends RegistrationEventSimpleMapperImpl {
    private final UserRegistrationRepository userRegistrationRepository;
    @Override
    public BaseRegistrationEventDTO toDto(RegistrationEvent entity) {
        BaseRegistrationEventDTO baseRegistrationEventDTO = super.toDto(entity);
        Long registrationEventId = baseRegistrationEventDTO.getId();
      baseRegistrationEventDTO.setTotalRegister(
         this.userRegistrationRepository.countByRegistrationEventId(registrationEventId));
        return baseRegistrationEventDTO;
    }
}