Java:Commons-Collections泛型:如何使自定义变换器工作

Question

嗨,我正在使用commons集合泛型4.01.

我有一个dto对象.

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

   // getters and setters
}

我有一份清单 List<PricingDto> pricingDtos = this.pricingService.getAllPricings();

比我有一个私人静态类.

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. 
            }
        }
    }
}

我的问题是我得到类强制转换异常,因为totalList中的每个项目都是PricingDto而不是Double.

2.)我做错了什么.什么是为generics commons-collections实现自定义变换器的正确方法.

Answer 1

该Javadoc中明确指出:

如果列表中已有任何元素被装饰,则不会对它们进行转换.

请尝试以下方法:

CollectionUtils.transform(pricingDtos, PRICING_DTO_TRANSFORMER);

这将通过将Transformer应用于每个元素来转换集合.