按三个字段分组，然后使用 Java8 Stream Collectors 和 EntrySet 求和 BigDecimal [重复]

Question

我有一个饮料数组列表

List<Beverage>beverages= Arrays.asList(
            new Beverage("Alcoholic","Can","Budweiser",new BigDecimal(5)),
            new Beverage("Alcoholic","Can","Budweiser",new BigDecimal(10)),
            new Beverage("Alcoholic","Bottle","Budweiser",new BigDecimal(15)),
            new Beverage("Alcoholic","Bottle","Budweiser",new BigDecimal(20)),
            new Beverage("Alcoholic","Can","Tecate",new BigDecimal(5)),
            new Beverage("Alcoholic","Bottle","Tecate",new BigDecimal(10)),
            new Beverage("Alcoholic","Bottle","Tecate",new BigDecimal(16)),
            new Beverage("Non-Alcoholic","Can","Coke",new BigDecimal(10)),
            new Beverage("Non-Alcoholic","Can","Coke",new BigDecimal(10)),
            new Beverage("Non-Alcoholic","Bottle","Coke",new BigDecimal(10)),
            new Beverage("Non-Alcoholic","Can","Pepsi",new BigDecimal(10)),
            new Beverage("Non-Alcoholic","Bottle","Pepsi",new BigDecimal(10)));

我的饮料 POJO 是

public class Beverage {
private String type;
private String containerType;   
private String itemName;
private BigDecimal quantity;
public Beverage(String type, String containerType, String itemName, BigDecimal quantity) {
    this.type = type;
    this.containerType = containerType;
    this.itemName = itemName;
    this.quantity = quantity;
}
public Beverage() {
}

}

我想按类型、containerType 和 itemName 对列表进行分组，并使用 Java8 Stream 收集器和 EntrySet 对 quatity 字段求和。

输出应在 ArrayList 中，如所附屏幕截图所示

Answer 1

你可以试试这个，

Map<String, Map<String, Map<String, Integer>>> result = beverages.stream()
                .collect(Collectors.groupingBy(Beverage::getType,
                        Collectors.groupingBy(Beverage::getContainerType,
                                Collectors.groupingBy(Beverage::getItemName,
                        Collectors.summingInt(b -> b.getQuantity().intValue())))));

输出

    {Non-Alcoholic={
                      Can={
                         Coke=20,
                         Pepsi=10
                      },
                      Bottle={
                            Coke=10,
                            Pepsi=10
                      }
                    },
     Alcoholic={
                     Can={
                        Tecate=5,
                        Budweiser=15
                     },
                     Bottle={
                        Tecate=26,
                        Budweiser=35
                     }
               }
   }