@Mapper(  collectionMappingStrategy = CollectionMappingStrategy.ADDER_PREFERRED )
public interface XyzMapper {

   XyzMapper INSTANCE = Mappers.getMapper( XyzMapper.class );

   @InheritConfiguration
   @Mapping( target = "targetElements", source = "sourceElements" )
   void map(Source source, @MappingTarget Target target);

   void map(SourceElement sourceElement, @MappingTarget TargetElement targetElement);
}

public class Source {

    private List<SourceElement> sourceElements;

    public List<SourceElement> getSourceElements() {
        return sourceElements;
    }

    public void setSourceElements(List<SourceElement> sourceElements) {
        this.sourceElements = sourceElements;
    }

}

public class Target {

    private List<TargetElement> targetElements = new ArrayList<>(  );

    public List<TargetElement> getTargetElements() {
        return targetElements;
    }

    public void setTargetElements(List<TargetElement> targetElements) {
        this.targetElements = targetElements;
    }

    public TargetElement addTargetElement( TargetElement elemnt) {
        getTargetElements().add( elemnt );
        return elemnt;
    }
}