Java实体类映射工具MapStruct

 MapStruct是一个属性映射工具，只需要自定义一个Mapper接口或者抽象的Mapper类，MapStruct就会自动为你实现该接或抽象方法，避免了映射实现的繁杂细节。官网地址：http://mapstruct.org/。

1、添加依赖

implementation 'org.mapstruct:mapstruct:1.3.1.Final'
annotationProcessor "org.mapstruct:mapstruct-processor:1.3.1.Final"

2、定义接口或抽象方法，并添加@Mapper

@Mapper(componentModel = "spring", nullValueMappingStrategy = NullValueMappingStrategy.RETURN_DEFAULT, unmappedTargetPolicy = ReportingPolicy.IGNORE，imports = {LocalDateTime.class})
public abstract class SPAQuoteMapper {
  
}

 @Mapper用于接口或者抽象类，重要属性解读：（1）nullValueMappingStrategy，如果源实体类的某个属性为null，映射到目标实体类的某个属性时，如何处理，有RETURN_NULL和RETURN_DEFAULT两个策略。（2）unmappedTargetPolicy，如果目标实体类中的某些属性在源实体类中无可以映射的属性，如何处理，详情参考：https://www.baeldung.com/mapstruct-ignore-unmapped-properties。（3）imports，MapStruct会自动为接口或者抽象类生成一个实现类，import相当于为实现类声明需要import的类。

3、添加映射方法

@Mapper(componentModel = "spring", nullValueMappingStrategy = NullValueMappingStrategy.RETURN_DEFAULT, unmappedTargetPolicy = ReportingPolicy.IGNORE，imports = {LocalDateTime.class})
public abstract class SPAQuoteMapper {

 	@Mapping(source = "press.location", target = "pressDTO.place")
	@Mapping(source = "press.location", target = "pressDTO.place", qualifiedByName = "toBigDecimal")
	documentDTO documentTodocumentDTO(document entity);
	
	@Named("toBigDecimal")
	private BigDecimal changeStringToDecimal(String number) {
		return new BigDecimal(number);
	}
}

 相关实体类如下:

public class documentDTO {
    private int id;
    private String title;
    private String text;
    private PressDTO pressDTO;
    private List comments;
    private String author;
}

public class PressDTO {
    private String place;
    private String name;
    private BigDecimal assetsAmount;
}

public class document {
    private int id;
    private String title;
    private String text;
    private Press press;
    private Date modificationTime;
}

public class Press {
    private String location;
    private String name;
    private String assetsVolume;
}  

4、使用

IngressOrderMapper ingressOrderMapper = Mappers.getMapper(IngressOrderMapper.class);