Joda time plusDays 得到错误的日期

Question

我正在使用此代码：

 DateTime(date)//Thu Aug 06 00:00:00 GMT+03:00 2020
                .plusDays(days) // 103
                .toDate()

结果是 Fri Dec 18 23:00:00 GMT+02:00 2020 而不是 Dec 19。对于某些日期它运行良好，对于其他结果 date-1，我猜问题出在一个月中的天数上，但是 plusDays() 不考虑它吗？

Answer 1

With some dates it work well, with other the result date-1, I guess the problem is with number of days in month, but does plusDays() not consider it?

确实考虑到了。您提到的两个 date-time 字符串的问题在于它们属于不同的 Zone-Offset （第一个是 UTC+3，第二个是 UTC+2）。下面给出了如何使用相同的 Zone-Offset.

import org.joda.time.DateTime;
import org.joda.time.DateTimeZone;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        DateTimeFormatter formatter = DateTimeFormat.forPattern("EEE MMM dd HH:mm:ss zZ yyyy");
        DateTime dateTime = DateTime.parse("Thu Aug 06 00:00:00 GMT+03:00 2020", formatter);
        System.out.println(dateTime);
        // With Zone-Offset of UTC+2
        System.out.println(dateTime.withZone(DateTimeZone.forOffsetHours(2)));

        // Add 103 days
        DateTime dateTimeAfter103Days = dateTime.plusDays(103);
        System.out.println(dateTimeAfter103Days);
        System.out.println(dateTime.withZone(DateTimeZone.forOffsetHours(2)));
    }
}

输出：

2020-08-05T21:00:00.000Z
2020-08-05T23:00:00.000+02:00
2020-11-16T21:00:00.000Z
2020-08-05T23:00:00.000+02:00

我推荐你使用modern java.time date-time API and the corresponding formatting API (package, java.time.format). Learn more about the modern date-time API from Trail: Date Time. If your Android API level is still not compliant with Java8, check and Java 8+ APIs available through desugaring。

下面的table显示一个overview of modern date-time classes：

与现代date-time API:

import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        // Define formatter for your date-time string
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss O u");

        // Parse the given date0-time string into OffsetDateTime object
        OffsetDateTime dateTime = OffsetDateTime.parse("Thu Aug 06 00:00:00 GMT+03:00 2020", formatter);
        System.out.println(dateTime);

        // Add 103 days to the OffsetDateTime object
        OffsetDateTime dateTimeAfter103Days = dateTime.plusDays(103);
        System.out.println(dateTimeAfter103Days);
    }
}

输出：

2020-08-06T00:00+03:00
2020-11-17T00:00+03:00

或者，

import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        // Define formatter for your date-time string
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss z yyyy");

        // If you do not need Zone Id or Zone Offset information, you can go for
        // LocalDateTime
        LocalDateTime dateTime = LocalDateTime.parse("Thu Aug 06 00:00:00 GMT+03:00 2020", formatter);
        System.out.println(dateTime);

        // You can convert LocalDateTime object into an OffsetDateTime by applying the
        // Zone-Offset e.g. the following line applies UTC+03:00 hours to LocalDateTime
        OffsetDateTime odt = dateTime.atOffset(ZoneOffset.ofHours(3));
        System.out.println(odt);

        // Add 103 days to the LocalDateTime object
        LocalDateTime dateTimeAfter103Days = dateTime.plusDays(103);
        System.out.println(dateTimeAfter103Days);

        odt = dateTimeAfter103Days.atOffset(ZoneOffset.ofHours(3));
        System.out.println(odt);
    }
}

输出：

2020-08-06T00:00
2020-08-06T00:00+03:00
2020-11-17T00:00
2020-11-17T00:00+03:00

Answer 2

您可以使用 java.time，较低的 Android API 支持它，因为现在有 API desugaring in Android。

有一个 zone-aware class (java.time.ZonedDateTime) 和一个 offset-aware (java.time.OffsetDateTime)，但是你的例子 String 只包含GMT / UTC 的偏移量。这就是为什么我会使用 OffsetDateTime 来解析确切的时间然后添加一天。

这是一个简单的示例，它定义了一个格式化程序，它解析给定的 String 并将其用于输出：

public static void main(String[] args) {
    // example String
    String date = "Fri Dec 18 23:00:00 GMT+02:00 2020";
    // create a formatter that is able to parse and output the String
    DateTimeFormatter dtf = DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss OOOO uuuu",
                                                        Locale.ENGLISH);
    // parse the String using the formatter defined above
    OffsetDateTime odt = OffsetDateTime.parse(date, dtf);
    System.out.println("OffsetDateTime parsed is\t" + odt.format(dtf));
    
    // add a day to the date part
    OffsetDateTime dayLater = odt.plusDays(1);
    System.out.println("Adding a day results in\t\t" + dayLater.format(dtf));
}

这输出

OffsetDateTime parsed is    Fri Dec 18 23:00:00 GMT+02:00 2020
Adding a day results in     Sat Dec 19 23:00:00 GMT+02:00 2020

如果您只对输出日期感兴趣（没有时间部分或偏移量），在那些 classes 中还有另一个方便的东西，那就是轻松提取日期或 time-part。您可以使用 OffsetDateTime 执行以下操作，例如：

// extract the part that only holds information about day of month, month of year and year
LocalDate dateOnly = odt.toLocalDate();
// print the default format (ISO standard)
System.out.println(dateOnly);
// or define and use a totally custom format
System.out.println(dateOnly.format(
                        DateTimeFormatter.ofPattern("EEEE, 'the' dd. 'of' MMMM uuuu",
                                                    Locale.ENGLISH)
                    )
);

那会输出

2020-12-18
Friday, the 18. of December 2020

如果您正在处理 DatePicker datePicker，您可以通过 getYear()、getMonth() 和 getDayOfMonth() 接收选定的值，然后创建一个

LocalDate localDate = LocalDate.of(datePicker.getYear(),
                                   datePicker.getMonth(), 
                                   datePicker.getDayOfMonth());

然后通过 localDate.plusDays(1);

添加一天

Joda time plusDays 得到错误的日期

Joda time plusDays getting wrong date

java

datetime

android

jodatime

android-jodatime