Java: Collections of collections of collections: how to make a custom transformer work

Question

Hi, I use the collections of general collections 4.01.

I have a dto object.

Class PricingDto {
   private Double tax;
   private Double price;
   private Double tip;

   // getters and setters
}

I have a list List<PricingDto> pricingDtos = this.pricingService.getAllPricings();

than I have a private static class.

import org.apache.commons.collections15.Transformer;
import org.apache.commons.collections15.list.TransformedList;

class TotalServiceImpl implements TotalService {
    public static final PricingDtoTransformer PRICING_DTO_TRANSFORMER =
        new PricingDtoTransformer();
    private static class PricingDtoTransformer
        implements Transformer<PricingDto, Double> {
        public PricingDtoTransformer() {}

        @Override
        public Double transform(final PricingDto pricingDto) {
            return pricingDto.getTax()
                     + pricingDto.getPrice()
                     + pricingDto.getTips();
        }
    }

    @Override
    public List<Double> getListDouble(final List<PricingDto> pricingDtos) {
        final List<Double> totalList = 
            TransformedList.decorate(pricingDtos, PRICING_DTO_TRANSFORMER);
            for (Double d : totalList) {
                // print them. 
            }
        }
    }
}

My problem is that I get a class exception, because each element in totalList is PricingDto, not Double.

2.) What I did wrong. What is the right way to implement a custom transformer for common collections collections.

Answer 1

. Google Guava. Lists.transform(List,Function) , , .

:

class TotalServiceImpl implements TotalService{

    private static final Function<PricingDto, Double> PRICING_DTO_TRANSFORMER =
        new PricingDtoTransformer();

    private static class PricingDtoTransformer implements
        Function<PricingDto, Double>{

        public PricingDtoTransformer(){
        }

        @Override
        public Double apply(final PricingDto pricingDto){
            return pricingDto.getTax() + pricingDto.getPrice()
                + pricingDto.getTips();
        }
    }

    public List<Double> getListDouble(final List<PricingDto> pricingDtos){
        final List<Double> totalList =
            Lists.transform(pricingDtos, PRICING_DTO_TRANSFORMER);
        for(final Double d : totalList){
            // print them.
        }
        return totalList;
    }

}

Commons-Collections , .

Answer 2

javadocs , :

- , , , .

:

CollectionUtils.transform(pricingDtos, PRICING_DTO_TRANSFORMER);

, .