java 8上的spring迭代值

Question

我在Java8中有以下代码

List<CategoryTranslation> categoriesTranslation = categoriesRepository.findByLanguageId(languageId);
List<CategoryDTO> categoryList = categoriesTranslation
.stream()
.map(x -> categoriesAdapter.category2DTO(x))                
.collect(Collectors.toList());

这是正确的，但我需要像这样转换

   List<CategoryTranslation> categoriesTranslation = categoriesRepository.findByLanguageId(languageId);
    List<CategoryDTO> categoryList = new ArrayList<CategoryDTO>();
   for (CategoryTranslation categoryTranslation : categoriesTranslation) {
                    CategoryDTO categoryDTO = categoriesAdapter.category2DTO(categoryTranslation);
                    categoryDTO.setTotal(categoryRepository.countTotalArticlesByCategory(categoryDTO.getCategoryId(), languageId));
                    categoryList.add(categoryDTO);
                }

我知道我可以使用适配器，但我不喜欢在适配器中使用JPA

Answer 1

只需创建一个方法categorty2DTOWithTotal(CategoryTranslation ct, Long? languiageId)。 否则，您必须调用forEach，但它是一个终止方法，因此您无法将其分组到列表中。从理论上讲，如果设置total会产生合理的映射，您可以引入一种方法来实现这一点，但在这里似乎有点牵强

void aMethod(Long? languageId) {
    List<CategoryTranslation> categoriesTranslation = categoriesRepository
        .findByLanguageId(languageId);
    List<CategoryDTO> categoryList = categoriesTranslation
        .stream()
        .map(x -> category2DTOWithTotal(x, languageId))                
        .collect(Collectors.toList());
}

CategoryDTO category2DTOWithTotal(CategoryTranslation ct, Long? languageId) {
    CategoryDTO categoryDTO = categoriesAdapter.category2DTO(categoryTranslation);
    categoryDTO.setTotal(
        categoryRepository.countTotalArticlesByCategory(
            categoryDTO.getCategoryId(), languageId
        )
    );
    return categoryDTO;
}

或者，您可以稍后设置总计：

void aMethod(Long? languageId) {
    List<CategoryDTO> categoryList = categoriesTranslation
        .stream()    
        .map(categoriesAdapter::category2DTO)                
        .collect(Collectors.toList());

    categoryList.forEach(dto -> dto.setTotal(
        categoryRepository.countTotalArticlesByCategory(
            categoryDTO.getCategoryId(), languageId
        )
    );
}

为完整起见，可映射版本的setting total：

void aMethod(Long? languageId) {
    List<CategoryTranslation> categoriesTranslation = categoriesRepository
        .findByLanguageId(languageId);
    List<CategoryDTO> categoryList = categoriesTranslation
        .stream()
        .map(categoriesAdapter::category2DTO)
        .map(x -> setTotal(x, languageId))
        .collect(Collectors.toList());
}

CategoryDTO setTotal(CategoryDTO ctd, Long? languageId) {
    ctd.setTotal(
        categoryRepository.countTotalArticlesByCategory(ctd.getCategoryId(), languageId)
    );
    return ctd;
}