Converting a list of items to a single object

Question

I need to convert a list of items to a single dto item. In case there are any elements in the list, we take the first one. I implemented the converter interface this way, but it doesn't work. The destination item is null after the conversion.

public class LocationConverter implements Converter<List<Location>,LocationDto> {

@Override
public LocationDto convert(MappingContext<List<Location>, LocationDto> mappingContext) {
    ModelMapper modelMapper = new ModelMapper();
    List<Location> locations = mappingContext.getSource();
    LocationDto locationDto = mappingContext.getDestination();
    if (locations.size() >= 1) {
        Location location = locations.get(0);
        modelMapper.map(location, locationDto);
        return locationDto;
    }
    return null;
   }
}

 ModelMapper modelMapper = new ModelMapper();
 modelMapper.addConverter(new LocationConverter());
 Event event = new Event();
 modelMapper.map(event, eventDto);

The entities on which I apply this converter look so:

public class Event extends BasicEntity  {

  private Integer typeId;

  private String typeName;

  private List<Location> locationList;

}


public class EventDto {

    private Integer typeId;

   private String typeName;

   private LocationDto location;
}

So I need the list of locations in Event to be converted into LocationDto in EventDto.

Answer 1

We can define a converter for each property mapping, that means we cam map locationList to location with custom converter.

With Java8

modelMapper.typeMap(Event.class, EventDto.class).addMappings(
        mapper -> mapper.using(new LocationConverter()).map(Event::getLocationList, EventDto::setLocation));

With Java 6/7

modelMapper.addMappings(new PropertyMap() {
    @Override
    protected void configure() {
        using(new LocationConverter()).map().setLocation(source.getLocationList());
    }
});