Common Aproaches to reduce code-overhead when using MapStruct in Spring Boot

In c# the library https://docs.automapper.org/en/stable/Getting-started.html exists. It allows us to specify all Mappers/Mappings in one File - MapStruct forces me to create a new interface for every Mapper, which results in a lot of files i have to create and clutters the project.

Is there any way to write these mappers in a way that they are all in one file at least, or that they can be configured programatically? I looked at alternatives like ModelMapper or JMaper, but they are not well maintained or way slower.

EDIT: i added sample code to illustrate the problem and highlight my issues with the current answer

public abstract class ProductMapper {
  public abstract ProductDto convertToDto(Product Product);

  public abstract Product convertToEntity(ProductDto checkoutProductDto);

  public abstract List<ProductDto> convertToDtos(List<Product> entities);

  public abstract List<Product> convertToEntities(List<ProductDto> dtos);
// below not working because of type erasure, so cant do it in the same file
  public abstract List<ProductOrderDetails> convertToEntities(List<ProductOrderDetailsDto> entities);

My project has hundreds of DTOs, most of them just requiring these 4 methods and no AfterMapping. Making these by hand is a giant waste of time, are there any better approaches?

Edit: i got a better answer from the mapstruct devs: https://github.com/mapstruct/mapstruct/issues/3111

Solution

Creating an abstract class with the 4 base methods, but with generic types seems like it would solve the issue. You'd still need to create the interface manually but the 4 methods would be already defined.

Here's an example in kotlin of what I mean.

These classes and mappers ( I've used kotlin only for convenience, but the mappers are still generated in java ) :

package mapper

import org.mapstruct.Mapper

abstract class EntityMapper<A, B>() {

    abstract fun toDto(a: A): B
    abstract fun toEntity(b: B): A
}

data class Device(val id: String)
data class DeviceDto(val id: String)

@Mapper
abstract class DeviceMapper : EntityMapper<Device, DeviceDto>()

data class OtherDevice(val id: String)
data class OtherDeviceDto(val id: String)

@Mapper
abstract class OtherDeviceMapper : EntityMapper<OtherDevice, OtherDeviceDto>()

Make mapstruct generate these 2 following mappers:

@Component
public class DeviceMapperImpl extends DeviceMapper {

    @Override
    public DeviceDto toDto(Device a) {
        if ( a == null ) {
            return null;
        }

        String id = null;

        id = a.getId();

        DeviceDto deviceDto = new DeviceDto( id );

        return deviceDto;
    }

    @Override
    public Device toEntity(DeviceDto b) {
        if ( b == null ) {
            return null;
        }

        String id = null;

        id = b.getId();

        Device device = new Device( id );

        return device;
    }
}

And

@Component
public class OtherDeviceMapperImpl extends OtherDeviceMapper {

    @Override
    public OtherDeviceDto toDto(OtherDevice a) {
        if ( a == null ) {
            return null;
        }

        String id = null;

        id = a.getId();

        OtherDeviceDto otherDeviceDto = new OtherDeviceDto( id );

        return otherDeviceDto;
    }

    @Override
    public OtherDevice toEntity(OtherDeviceDto b) {
        if ( b == null ) {
            return null;
        }

        String id = null;

        id = b.getId();

        OtherDevice otherDevice = new OtherDevice( id );

        return otherDevice;
    }
}