MapStruct QualifiedByName with multiple parameters

Currently MapStruct does not support mapping methods with multiple source properties.

However, in your case you can use the @Context from 1.2.0. From what I understand the projId and the code are there just as helper of the mapping, and they are not used to map target properties from.

So you can do something like (It should work in theory):

@Mapper
public interface OneMapper {

    @Mapping(target="id", source="one.id")
    @Mapping(target="qualified", qualifiedByName="checkQualifiedNamed")
    OneDto createOne (One one, @Context Integer projId, @Context String code);

    @Named("checkQualifiedNamed")
    default Boolean checkQualified (One one, @Context Integer projId, @Context String code) {
        if(one.getProjectId() == projId && one.getCode().equalsIgnoreCase(code)) {
            return Boolean.TRUE;
        }
        return Boolean.FALSE;                   
    }
}

Another alternative would be to extract all those properties into a separate class and pass that along (this would allow for multiple parameters of the same type).

The class would look like:

public class Filter {

    private final Integer projId;
    private final Integer val;
    private final String code;

    public Filter (Integer projId, Integer val, String code) {
        this.projId = projId;
        this.val = val;
        this.code = code;
    }

    //getters
}

Your mapper will then look like:

@Mapper
public interface OneMapper {

    @Mapping(target="id", source="one.id")
    @Mapping(target="qualified", qualifiedByName="checkQualifiedNamed")
    OneDto createOne (One one, @Context Filter filter);

    @Named("checkQualifiedNamed")
    default Boolean checkQualified (One one, @Context Filter filter) {
        if(one.getProjectId() == filter.getProjId() && one.getVal() == filter.getVal() && one.getCode().equalsIgnoreCase(filter.getCode())) {
            return Boolean.TRUE;
        }
        return Boolean.FALSE;                   
    }
}

You can then call the mapper like: mapper.createOne(one, new Filter(projId, val, code));

If you need to calculate a single target field based on multiple source fields from the same source object, you can pass the full source object to the custom mapper function instead of individual fields:

Example Entity:

@Entity
@Data
public class User {
    private String firstName;
    private String lastName;
}

Example DTO:

public class UserDto {
    private String fullName;
}

... and the mapper... Instead of passing a single source (firstName):

@Mapper
public abstract class UserMapper {

    @Mapping(source = "firstName", target = "fullName", qualifiedByName = "nameTofullName")
    public abstract UserDto userEntityToUserDto(UserEntity userEntity);


    @Named("nameToFullName")
    public String nameToFullName(String firstName) {
        return String.format("%s HOW DO I GET THE LAST NAME HERE?", firstName);
    }

... pass the full entity object (userEntity) as the source:

@Mapper
public abstract class UserMapper {

    @Mapping(source = "userEntity", target = "fullName", qualifiedByName = "nameToFullName")
    public abstract UserDto userEntityToUserDto(UserEntity userEntity);


    @Named("nameToFullName")
    public String nameToOwner(UserEntity userEntity) {
        return String.format("%s %s", userEntity.getFirstName(), userEntity.getLastName());
    }

Since version 1.2 it is supported: http://mapstruct.org/documentation/stable/reference/html/#mappings-with-several-source-parameters

For example like this:

@Mapping(source = "person.description", target = "description")
@Mapping(source = "address.houseNo", target = "houseNumber")
DeliveryAddressDto personAndAddressToDeliveryAddressDto(Person person, Address address);

UPDATE

Since Mapstruct allows to map multiple source arguments into a single target, I would advise to extract the checkQualified method from the mapper and instead compute the outcome beforehand and invoke the mapper with the result of the checkQualified method. Mapstruct is a mapping library, and does not excel in performing arbitrary logic. It's not impossible, but personally, I don't see the value it adds in your particular case.

With the logic extracted your mapper could look like this:

@Mapper
public interface OneMapper {
    OneDto toOneDto(One one, Boolean qualified);
}

The mapper can be used like this:

One one = new One(1, 10, 100, "one");
boolean qualified = checkQualified(one, 10, 100, "one");
boolean notQualified = checkQualified(one, 10, 100, "two");
OneDto oneDto = mapper.toOneDto(one, isQualified);

For a full example, see: https://github.com/phazebroek/so-mapstruct/blob/master/src/main/java/nl/phazebroek/so/MapStructDemo.java