Modelmapper: Map an element in a list to field in POJO

Question

public class SimpleDTO{
    private String firstElement;
    private String lastElement;
}

public class ComplexSource{
    private List<String> elementList;
}

I tried to map it usingmap().setFirstElement(source.getElementList().get(0)) but I get an error stating "1) Invalid source method java.util.List.get(). Ensure that method has zero parameters and does not return void."

How do I map an element in a list to a field in a Pojo using ModelMapper or any other alternative?

Pau · Answer 1 · 2016-11-12T09:16:45.703

In this case is you can't use a PropertyMap. If you want map it using ModelMapper you must use a Converter instead of PropertyMap as you have done.

First your Converter would be as next where the source is ComplexSource and SimpleDTO is the destination:

Converter<ComplexSource, SimpleDTO> converter = new AbstractConverter<ComplexSource, SimpleDTO>() {
    @Override
    protected SimpleDTO convert(ComplexSource source) {
        SimpleDTO destination = new SimpleDTO();
        List<String> sourceList = source.getElementList();

        if(null != sourceList && !sourceList.isEmpty()){
            int sizeList = sourceList.size();

            destination.setFirstElement(sourceList.get(0));
            destination.setLastElement(sourceList.get(sizeList - 1));
        }

        return destination;
    }
};

Then you just need to add the converter to your ModelMapper instance:

ModelMapper mapper = new ModelMapper();
mapper.addConverter(converter);

If you try the map, it works perfectly:

ComplexSource complexSource = new ComplexSource();
complexSource.setElementList(Arrays.asList("firstElement", "lastElement"));

SimpleDTO simpleDto = mapper.map(complexSource, SimpleDTO.class);
System.out.println(simpleDto);

Output

SimpleDTO [firstElement=firstElement, lastElement=lastElement]

Respect your comment, you need to check nulls if it is need in your source instance (in this case it is possible a null pointer if the list is null). But it inits for you the destination instance, even you can configure the destination instance how you want with a Provider (Providers documentation).

In cases of special use cases like this, you need to worry about null checks and exceptions handling because a Converter I would say is the way of modelmapper to map manually pojos.

The advantadges of use ModelMapper are explained in its web:

If you configure it correctly in some cases it is no need to do the map manually.
It centralizes the mapping.
It provides a mapping API for handling special use cases. (This is your case)
And so on (take a look its web)

Thanks! Tangential question, whats the advantage of using a ModelMapper vs using a simple mapper method to convert one object to another? I assumed that I wouldn't have to worry about the null checks and exception handling with a third party mapper, but seems like I am wrong on my assumption. — Matrix, Nov 11 '16 at 16:32

Modelmapper: Map an element in a list to field in POJO

1 Answers1