要在没有自定义收集器的情况下执行此操作(不再对结果进行流式传输),您可以这样做.它有点脏,因为它首先收集到Map< String,List< TimePeriodCalc>>然后流式传输该列表并获得平均加倍.

由于你需要两个平均值,它们被收集到一个Holder或一对,在这种情况下我使用的是AbstractMap.SimpleEntry

Map> map = Stream.of(new TimePeriodCalc(12d, 10d, "A"), new TimePeriodCalc(2d, 16d, "A"))

.collect(Collectors.groupingBy(TimePeriodCalc::getAtDate,

Collectors.collectingAndThen(Collectors.toList(), list -> {

double occupancy = list.stream().collect(

Collectors.averagingDouble(TimePeriodCalc::getOccupancy));

double efficiency = list.stream().collect(

Collectors.averagingDouble(TimePeriodCalc::getEfficiency));

return new AbstractMap.SimpleEntry<>(occupancy, efficiency);

})));

System.out.println(map);