如何汇总对象列表的各个字段并以单个对象的形式返回结果

让我们介绍一下课程

NutritionAccumulator

class NutritionAccumulator{    private double fat = 0.;    private double carbs = 0.;    private double fiber = 0.;    private double protein = 0.;    public NutritionAccumulator() {    }    public NutritionAccumulator(double fat, double carbs, double fiber, double protein) {        this.fat = fat;        this.carbs = carbs;        this.fiber = fiber;        this.protein = protein;    }    public NutritionAccumulator add(NutritionAccumulator that){        return new NutritionAccumulator(this.fat + that.fat,        this.carbs + that.carbs,        this.fiber + that.fiber,        this.protein + that.protein        );    }}

现在我们可以编写简单的stream reduce：

Optional.ofNullable(response.body()).stream().reduce(  new NutritionAccumulator(),  (acc, fudNut) -> new NutritionAccumulator(          fudNut.getTotalFat(),          fudNut.getTotalCarbohydrate(),          fudNut.getDietaryFiber(),          fudNut.getProtein()  ).add(acc),  NutritionAccumulator::add     );

最后，您可以将结果从上方传递给生成器。