想要通过按属性对其他对象列表进行分组来创建新列表

Question

想要通过按属性对其他对象列表进行分组来创建一个列表代码是这样的：

public class MyDate {
    public static void main(String[] args) {

        List<Data> list = new ArrayList<>();
        list.add(new Data("NEW",todayDate,todayDatePlus1,"N"));
        list.add(new Data("AUTORIZED",todayDate,todayDatePlus1,"Y"));
        list.add(new Data("AUTORIZED",todayDatePlus1,todayDatePlus3,"Y"));
        list.add(new Data("AUTHENTICATE",todayDate,todayDatePlus1,"Y"));
        list.add(new Data("AUTHENTICATE",todayDatePlus1,todayDatePlus2,"Y"));
        list.add(new Data("COMPLETED",todayDate,todayDatePlus1,"N"));

    }
}

@Getter
@Setter
class Data{
    String phase;
    LocalDate startDate;
    LocalDate endDate;
    String required;
    
    Data(String phase,  LocalDate startDate, LocalDate endDate, String required) {
        this.phase = phase;
        this.startDate = startDate;
        this.endDate = endDate;
        this.required = required;
    }
}

输出：

In New List 

("NEW",todayDate,todayDatePlus1,"N")
**("AUTORIZED",todayDate,todayDatePlus3,"Y")**
**("AUTHENTICATE",todayDate,todayDatePlus2,"Y")**
("COMPLETED",todayDate,todayDatePlus1,"N")

在新列表中，重复的属性phase 合并为1，并且StartDate 和EndDate 也被更新。（StartDate 最早一个，EndDate 是最后一个）

Answer 1

您可以使用 Collectors.toMap 和 mergefunction，合并具有相同 phase

的 Data 对象的值

 Collection<Data> result = list.stream()
            .collect(Collectors.toMap(Data::getPhase, Function.identity(), ((existing, replacement) -> {

                // Merge values of replacement with existing
                existing.setEndDate(replacement.getEndDate());
                return existing;
            }))).values();

想要通过按属性对其他对象列表进行分组来创建新列表

Want to create a new list by grouping the other list of objects by attribute

java

grouping

list