如何在流（java）中添加dateTime值？ [英] How to add dateTime values in a stream(java)?

问题描述

今天我开始学习Java 8，所以我对Java 8很陌生。
我有一份活动清单。活动具有name，startTime，endTime。对于startTime和endTime，我正在使用joda时间的DateTime。

Today I started learning Java 8, so I'm quite new to Java 8 and it's stuff. I have a list of activities. An activity has name, startTime, endTime. For startTime and endTime i'm using DateTime from joda time.

我正在尝试确定映射$ b的表单Map（String，DateTime）的数据结构每个活动$ b在监控期内计算的总持续时间。

I'm trying to determine a data structure of the form Map (String, DateTime) that maps for each activity the total duration computed over the monitoring period.

以下是我的代码片段：

import java.util.ArrayList;
import java.util.Map;
import org.joda.time.DateTime;

class Activity {
public DateTime startTime;
public DateTime endTime;
public String activityLabel;

public Activity(DateTime startTime, DateTime endTime, String activityLabel) {
    super();
    this.startTime = startTime;
    this.endTime = endTime;
    this.activityLabel = activityLabel;
}
}

public class Main {

public static void main(String[] args) {
    ArrayList<Activity> list = new ArrayList<>();
//adding activities to list

    list.add(new Activity(new DateTime(2017, 5, 12, 13, 10, 0), new DateTime(2017, 5, 12, 13, 40, 0), "Showering"));
    list.add(new Activity(new DateTime(2017, 5, 12, 13, 41, 0), new DateTime(2017, 5, 12, 14, 20, 0), "Cooking"));
    list.add(new Activity(new DateTime(2017, 5, 12, 14, 20, 0), new DateTime(2017, 5, 12, 14, 50, 0), "Eating"));
    list.add(new Activity(new DateTime(2017, 5, 12, 14, 51, 0), new DateTime(2017, 5, 12, 15, 30, 0), "Sleeping"));
    list.add(new Activity(new DateTime(2017, 5, 12, 17, 22, 0), new DateTime(2017, 5, 12, 17, 30, 0), "Showering"));
    list.add(new Activity(new DateTime(2017, 5, 12, 17, 41, 0), new DateTime(2017, 5, 12, 17, 50, 0), "Cooking"));
    list.add(new Activity(new DateTime(2017, 5, 12, 17, 50, 0), new DateTime(2017, 5, 12, 18, 20, 0), "Eating"));
    list.add(new Activity(new DateTime(2017, 5, 12, 18, 21, 0), new DateTime(2017, 5, 12, 20, 30, 0), "TV"));
//creating a stream from list
    Map<String, DateTime> map;
//  map = list.stream().collect(Collectors.groupingBy(s -> s.activityLabel, Collectors.  ... 

}

}

我不知道如何获得这个结果:(。我尝试了不同的方法，我无法知道如何获得每个活动的总持续时间...谢谢你帮助我！

I don't know how to obtain this result :(. I tried different methods and i couldn't find out how obtain the total duration for each activity... Thank you for helping me!

推荐答案

首先开始使用Java 8 DateTime API。有一个内置的 Duration 类。然后你可以使用：

First start to use Java 8 DateTime API. There is a built-in Duration class. Then you can use:

Map<String, Duration> map = list.stream().collect(
    Collectors.groupingBy(a -> a.activityLabel, 
        Collectors.reducing(Duration.ZERO, 
            a -> Duration.between(a.startTime, a.endTime).abs(), Duration::plus
        )
    ));

---

编辑

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EDIT

由于您要使用 Joda ，您可以获得相同的结果（使用期而不是持续时间）：

Since you've to use Joda you can get the same results with (using Period instead of Duration):

Map<String, Period> map = list.stream().collect(
    Collectors.groupingBy(a -> a.activityLabel, 
        Collectors.reducing(Period.ZERO, 
            a -> new Period(a.startTime, a.endTime), Period::plus
        )
    ));

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