Java:CommonCollections泛型：如何让自定义转换器工作

Question

大家好，我正在使用commons collections generics 4.01

我有一个dto对象

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

   // getters and setters
}

我有一个List<PricingDto> pricingDtos = this.pricingService.getAllPricings();的列表

我有一个私人的静态类

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. 
            }
        }
    }
}

我的问题是我得到了类cast异常，因为totalList中的每个项都是PricingDto，而不是Double

2.）我做错了什么。为泛型公共集合实现自定义转换器的正确方法是什么

Answer 1

对我来说，改变现有的藏品似乎是一个可怕的难题。我建议用Google Guava代替。它是^{}返回一个由原始列表和映射函数支持的视图，因此实际上您没有更改任何内容

下面是您的代码：

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可能也有类似的机制，但我一眼就找不到

Answer 2

报告明确指出：

If there are any elements already in the list being decorated, they are NOT transformed.

请尝试以下方法：

CollectionUtils.transform(pricingDtos, PRICING_DTO_TRANSFORMER);

这将通过将转换器应用于每个元素来转换集合