Java组由一个包含2个LocalDateTime字段的对象列表组成，然后从中获得最大值和最小值

Question

我得到了一个类调用TimeInterval，它有两个字段；startDate"；以及"；endDate"；，我得到了这样一个数据列表：

在这里列出，还有更多，但我认为这些已经足够了

我想做的是，以前6个结果为例，它的开始日期为"；2015-01-19"：

此处列出示例

现在我想按startDate对它们进行分组；小时；startDate的值；12〃；，并且还取最大值"0"；小时；endDate的值；4〃；。

我该如何做到这一点？我试着用stream分组，但我遇到了一个死胡同，不知道如何解决这个问题。

TimeInterval类：

public class TimeInterval {
private LocalDateTime startDate;
private LocalDateTime endDate;
public LocalDateTime getStartDate() {
return startDate;
}
public void setStartDate(LocalDateTime startDate) {
this.startDate = startDate;
}
public LocalDateTime getEndDate() {
return endDate;
}
public void setEndDate(LocalDateTime endDate) {
this.endDate = endDate;
}

public TimeInterval(LocalDateTime startDate, LocalDateTime endDate) {
this.startDate = startDate;
this.endDate = endDate;
}
@Override
public String toString() {
return "TimeInterval [startDate=" + startDate + ", endDate=" + endDate +"]";
}
}

数据：

TimeInterval [startDate=2015-01-19T12:00, endDate=2015-01-19T23:59:59]
TimeInterval [startDate=2015-01-19T13:00, endDate=2015-01-19T17:00]
TimeInterval [startDate=2015-01-19T15:30, endDate=2015-01-19T18:30]
TimeInterval [startDate=2015-01-19T17:00, endDate=2015-01-19T18:30]
TimeInterval [startDate=2015-01-19T18:00, endDate=2015-01-19T19:00]
TimeInterval [startDate=2015-01-19T19:00, endDate=2015-01-20T04:00]
TimeInterval [startDate=2015-01-20T06:00, endDate=2015-01-20T21:00]
TimeInterval [startDate=2015-01-20T07:00, endDate=2015-01-20T17:00]
TimeInterval [startDate=2015-01-20T08:00, endDate=2015-01-20T17:00]
TimeInterval [startDate=2015-01-20T08:15, endDate=2015-01-20T17:15]
TimeInterval [startDate=2015-01-20T09:00, endDate=2015-01-20T19:00]
TimeInterval [startDate=2015-01-20T10:00, endDate=2015-01-20T19:00]
TimeInterval [startDate=2015-01-20T10:15, endDate=2015-01-20T19:15]
TimeInterval [startDate=2015-01-20T11:00, endDate=2015-01-20T20:00]
TimeInterval [startDate=2015-01-20T11:30, endDate=2015-01-20T18:00]
TimeInterval [startDate=2015-01-20T12:00, endDate=2015-01-20T23:59:59]
TimeInterval [startDate=2015-01-20T13:00, endDate=2015-01-20T16:00]
TimeInterval [startDate=2015-01-20T15:00, endDate=2015-01-20T22:00]
TimeInterval [startDate=2015-01-20T15:30, endDate=2015-01-20T18:30]
TimeInterval [startDate=2015-01-20T18:00, endDate=2015-01-20T19:00]
TimeInterval [startDate=2015-01-20T19:00, endDate=2015-01-21T04:00]
TimeInterval [startDate=2015-01-21T00:00, endDate=2015-01-21T23:59:59]
TimeInterval [startDate=2015-01-21T07:00, endDate=2015-01-21T17:00]
TimeInterval [startDate=2015-01-21T07:30, endDate=2015-01-21T17:00]
TimeInterval [startDate=2015-01-21T07:45, endDate=2015-01-21T12:45]
TimeInterval [startDate=2015-01-21T08:00, endDate=2015-01-21T17:00]
TimeInterval [startDate=2015-01-21T08:30, endDate=2015-01-21T17:30]
TimeInterval [startDate=2015-01-21T09:00, endDate=2015-01-21T19:00]
TimeInterval [startDate=2015-01-21T10:00, endDate=2015-01-21T19:00]
TimeInterval [startDate=2015-01-21T11:00, endDate=2015-01-21T20:00]
TimeInterval [startDate=2015-01-21T11:30, endDate=2015-01-21T18:00]
TimeInterval [startDate=2015-01-21T12:00, endDate=2015-01-21T23:59:59]
TimeInterval [startDate=2015-01-21T13:00, endDate=2015-01-21T22:00]
TimeInterval [startDate=2015-01-21T14:00, endDate=2015-01-21T20:30]
TimeInterval [startDate=2015-01-21T15:00, endDate=2015-01-21T21:00]
TimeInterval [startDate=2015-01-21T15:30, endDate=2015-01-21T18:30]
TimeInterval [startDate=2015-01-21T18:00, endDate=2015-01-21T19:00]
TimeInterval [startDate=2015-01-21T19:00, endDate=2015-01-21T19:50]
TimeInterval [startDate=2015-01-22T00:00, endDate=2015-01-22T23:59:59]
TimeInterval [startDate=2015-01-22T01:00, endDate=2015-01-22T04:30]
TimeInterval [startDate=2015-01-22T07:00, endDate=2015-01-22T17:00]
TimeInterval [startDate=2015-01-22T08:00, endDate=2015-01-22T17:00]
TimeInterval [startDate=2015-01-22T09:00, endDate=2015-01-22T19:00]
TimeInterval [startDate=2015-01-22T09:30, endDate=2015-01-22T18:30]
TimeInterval [startDate=2015-01-22T10:00, endDate=2015-01-22T19:00]
TimeInterval [startDate=2015-01-22T11:00, endDate=2015-01-22T20:00]
TimeInterval [startDate=2015-01-22T11:30, endDate=2015-01-22T19:30]
TimeInterval [startDate=2015-01-22T12:00, endDate=2015-01-22T23:59:59]
TimeInterval [startDate=2015-01-22T13:00, endDate=2015-01-22T18:00]
TimeInterval [startDate=2015-01-22T14:00, endDate=2015-01-22T22:00]
TimeInterval [startDate=2015-01-22T15:30, endDate=2015-01-22T18:30]
TimeInterval [startDate=2015-01-22T18:00, endDate=2015-01-22T19:00]
TimeInterval [startDate=2015-01-22T19:00, endDate=2015-01-23T04:00]
TimeInterval [startDate=2015-01-23T00:00, endDate=2015-01-23T23:59:59]
TimeInterval [startDate=2015-01-23T05:00, endDate=2015-01-23T17:00]
TimeInterval [startDate=2015-01-23T06:00, endDate=2015-01-23T15:00]
TimeInterval [startDate=2015-01-23T07:00, endDate=2015-01-23T17:00]
TimeInterval [startDate=2015-01-23T07:45, endDate=2015-01-23T12:45]
TimeInterval [startDate=2015-01-23T08:00, endDate=2015-01-23T17:00]
TimeInterval [startDate=2015-01-23T08:15, endDate=2015-01-23T17:15]
TimeInterval [startDate=2015-01-23T09:00, endDate=2015-01-23T22:00]
TimeInterval [startDate=2015-01-23T09:30, endDate=2015-01-23T17:30]
TimeInterval [startDate=2015-01-23T10:00, endDate=2015-01-23T19:00]
TimeInterval [startDate=2015-01-23T10:30, endDate=2015-01-23T17:00]
TimeInterval [startDate=2015-01-23T11:00, endDate=2015-01-23T20:00]
TimeInterval [startDate=2015-01-23T11:30, endDate=2015-01-23T18:00]
TimeInterval [startDate=2015-01-23T12:00, endDate=2015-01-23T23:59:59]

Answer 1

假设您想要一个地图作为最终结果，您可以执行

• 按本地日期分组->Map<LocalDate, List<TimeInterval>>
• 流式传输结果映射的条目
• collect以使用相同的键(LocalDate(进行映射，并映射到新的TimeInterval对象，该对象具有来自条目值的最小startDate和最大endDate

示例：

Map<LocalDate, TimeInterval> result = 
sampleList.stream()
.collect(Collectors.groupingBy(t -> t.getStartDate().toLocalDate()))
.entrySet()
.stream()
.collect(Collectors.toMap(Entry::getKey,
e -> new TimeInterval(getMinDate(e.getValue()), getMaxDate(e.getValue()))));

使用两种辅助方法getMaxDate和getMinDate:

private static LocalDateTime getMaxDate(final List<TimeInterval> list) {
return list.stream()
.collect(Collectors.reducing(LocalDateTime.MIN,
TimeInterval::getStartDate,
BinaryOperator.maxBy(LocalDateTime::compareTo)));
}
private static LocalDateTime getMinDate(final List<TimeInterval> list) {
return list.stream()
.collect(Collectors.reducing(LocalDateTime.MAX,
TimeInterval::getStartDate,
BinaryOperator.minBy(LocalDateTime::compareTo)));
}

Answer 2

您可以使用Java Stream API使用startDate对它们进行分组，然后使用startDate和endDate对每个组的结果数据结构进行一次排序，以获得startDate和endDate的最小和最大元素。