我有以下对象:
class Event {
private LocalDateTime when;
private String what;
public Event(LocalDateTime when, String what) {
super();
this.when = when;
this.what = what;
}
public LocalDateTime getWhen() {
return when;
}
public void setWhen(LocalDateTime when) {
this.when = when;
}
public String getWhat() {
return what;
}
public void setWhat(String what) {
this.what = what;
}
我需要按照年/月(yyyy-mm)和事件类型进行汇总,然后进行计数。例如以下列表
List<Event> events = Arrays.asList(
new Event(LocalDateTime.parse("2017-03-03T09:01:16.111"), "EVENT1"),
new Event(LocalDateTime.parse("2017-03-03T09:02:11.222"), "EVENT1"),
new Event(LocalDateTime.parse("2017-04-03T09:04:11.333"), "EVENT1"),
new Event(LocalDateTime.parse("2017-04-03T09:04:11.333"), "EVENT2"),
new Event(LocalDateTime.parse("2017-04-03T09:06:16.444"), "EVENT2"),
new Event(LocalDateTime.parse("2017-05-03T09:01:26.555"), "EVENT3")
);
应该产生以下结果:
Year/Month Type Count
2017-03 EVENT1 2
2017-04 EVENT1 1
2017-04 EVENT2 2
2017-04 EVENT3 1
你知道是否可以使用Streams API实现这一功能吗?如果可以,应该如何实现呢?