How to use modelMapper to convert nested classes

I think if you configure your ModelMapper as LOOSE or STANDARD it will do for you.

modelMapper = new ModelMapper();
modelMapper.getConfiguration().setMatchingStrategy(MatchingStrategies.LOOSE);

Otherwhise you could try next:

1. You may create a converter like:

   public class ListThingToThingDTOConverter implements Converter<List<Thing>, List<ThingDTO>> {
   
   
   @Override
   public List<ThingDTO> convert(MappingContext<List<Thing>, List<ThingDTO>> context) {
       List<Thing> source = context.getSource();
       List<ThingDTO> output = new ArrayList<>();
       ...
       //Convert programmatically List<Thing> to List<ThingDTO>
       ...
   
       return output;
     }}
   

2. Then customize a Mapping Thing to ThingDTO as next:

       public class SourceToSourceDTOMap extends PropertyMap<Thing, ThingDTO> {
             @Override
             protected void configure(){
                  using(new ListThingToThingDTOConverter()).map(source.getThings()).setThings(null);
             }
   

3. Finally you must add SourceToSourceDTOMap to your ModelMapper as below:

   modelMapper = new ModelMapper();
   modelMapper.addMappings(new SourceToSourceDTOMap());
   

You can map like the below code by creating generics . link for reference

http://modelmapper.org/user-manual/generics/

imports :

import java.lang.reflect.Type;
import org.modelmapper.ModelMapper;
import org.modelmapper.TypeToken;

In your service or controller class:

ModelMapper modelMapper = new ModelMapper();
Type listType = new TypeToken<SourceDTO>(){}.getType();
SourceDTO sourceDTO = modelMapper.map(source,listType);