How to Map to Generic Type? - mapstruct

Question

PageInfoDto
public class PageInfoDto<T> implements Serializable {
private int currentPageNum;
private int totalPageNum;
private int perPageNum;
private int totalItemNum;
private List<T> list;
}
Page
public class Page<T> implements Serializable {
private int current;
private int total;
private int size;
private int items;
private List<T> list;
}
say, i have a school list and a student list.
i want to map Page to PageInfoDto and map Page to PageInfoDto。
this is how my mapper looks like;
#Mapper( config = CentralConfig.class, uses = {StudentMapper.class, SchoolMapper.class}, componentModel = "spring")
public interface PageInfoMapper {
#Mappings({
#Mapping(target = "list", source = "pageInfo.records"),
#Mapping(target = "currentPageNum", source = "pageInfo.current"),
#Mapping(target = "totalPageNum", source = "pageInfo.pages"),
#Mapping(target = "perPageNum", source = "pageInfo.size"),
#Mapping(target = "totalItemNum", source = "pageInfo.total"),
})
PageInfoDto<SchoolDto> toPageInfoDto1(Page<School> pageInfo);
#Mappings({
#Mapping(target = "list", source = "pageInfo.records"),
#Mapping(target = "currentPageNum", source = "pageInfo.current"),
#Mapping(target = "totalPageNum", source = "pageInfo.pages"),
#Mapping(target = "perPageNum", source = "pageInfo.size"),
#Mapping(target = "totalItemNum", source = "pageInfo.total"),
})
PageInfoDto<StudentDto> toPageInfoDto2(Page<Student> pageInfo);
}
this obviously not a clever way to do . is there a better way to do this？

Answer 1

Mapstruct is a code generator. So it needs to know which types to construct in order to generate a method implementation. Having said that, you could do this smarter by using a base mapping method on which you define all the #Mapping annotations and ignore the generic type mapping. You still have the methods above but you just specify #InheritConfiguration
Alternatively you could consider playing around with an objectfactory using #TargetType to construct the proper generic type. I'm not sure whether that works with a generic mapping method signature. I'm not in the position to check it, but let me know if that works
E.g.
public interface BasePageMapper<S, DTO> {
#Mapping(target = "list", source = "records"),
#Mapping(target = "currentPageNum", source = "current"),
#Mapping(target = "totalPageNum", source = "pages"),
#Mapping(target = "perPageNum", source = "size"),
#Mapping(target = "totalItemNum", source = "total"),
PageInfoDto<DTO> toPageInfoDto(Page<S> pageInfo);
DTO toDto(S source);
}
#Mapper( config = CentralConfig.class, uses = StudentMapper.class, componentModel = "spring")
public interface StudentMapper extends BasePageMapper<Student, StudentDto> {
}
#Mapper( config = CentralConfig.class, uses = SchoolMapper.class, componentModel = "spring")
public interface SchoolMapper extends BasePageMapper<School, SchoolDto> {
}