Question

我试图从ISO-8601日期格式字符串输入计算一年中的一周。最初我用java.time.ZonedDateTime尝试了这个，但它给输入日期 - 20-Jan-2049提供了错误的结果。然后我尝试使用Calendar API，它也给出了错误的响应，即31-Dec-2049。

我已附上示例测试代码

public class ZonedDateTimeTest {        
    public static void main(String[] args) throws InterruptedException {
        System.out.println("======================================");
        String instantStr1 = "2049-01-02T03:48:00Z";
        printYearAndWeekOfYear(instantStr1);
        System.out.println("======================================");
        String instantStr2 = "2049-12-31T03:48:00Z";
        printYearAndWeekOfYear(instantStr2);
        System.out.println("======================================");
    }

    public static void printYearAndWeekOfYear(String ISODate) {
        System.out.println("Date provided -> " + ISODate);

        ZonedDateTime utcTimestamp = parseToInstant(ISODate).atZone(ZoneOffset.UTC);
        int year = utcTimestamp.getYear();
        int weekOfYear = utcTimestamp.get(IsoFields.WEEK_OF_WEEK_BASED_YEAR);
        System.out.println("Using ZonedDateTime API:: Year " + year + " weekOfYear " + weekOfYear);


        Date d1 = Date.from(parseToInstant(ISODate));
        Calendar cl = Calendar.getInstance();
        cl.setTime(d1);
        int year1 = cl.get(Calendar.YEAR);
        int weekOfYear1 = cl.get(Calendar.WEEK_OF_YEAR);
        System.out.println("Using Calendar API:: Year " + year1 + " weekOfYear " + weekOfYear1);
    }

    public static Instant parseToInstant(String ISODate) {
        return DateTimeFormatter.ISO_OFFSET_DATE_TIME.parse(ISODate, Instant::from);
    }
}

上面代码的输出

======================================
Date provided  2049-01-02T03:48:00Z
Using ZonedDateTime API: Year 2049 weekOfYear 53
Using Calendar API: Year 2049 weekOfYear 1    
======================================    
Date provided 2049-12-31T03:48:00Z
Using ZonedDateTime API: Year 2049 weekOfYear 52
Using Calendar API: Year 2049 weekOfYear 1
======================================

Answer 1

您的代码有四个问题：

当您使用Calendar时，您正在使用系统默认时区，这可能会更改Instant落在哪个日期。如果您将日历设置为使用UTC，则会使其更加一致。
您正在使用Calendar.YEAR，这将为您提供日历年而不是周年。您需要使用Calendar.getWeekYear()代替。
您正在使用ZonedDateTime.getYear()，这又是日历年。你应该使用utcTimestamp.get(IsoFields.WEEK_BASED_YEAR)
您正在使用Calendar.getInstance()这可能会给您一个非公历日历，或者它可能会为您想要执行的计算设置不正确的第一天

修复这些问题（和命名约定）我们最终得到：

import java.util.*;
import java.time.*;
import java.time.format.*;
import java.time.chrono.*;
import java.time.temporal.*;

public class ZonedDateTimeTest {

    public static void main(String[] args) {
        printYearAndWeekOfYear("2049-01-02T03:48:00Z");
        String instantStr2 = "2049-12-31T03:48:00Z";
        printYearAndWeekOfYear("2049-12-31T03:48:00Z");
    }

    public static void printYearAndWeekOfYear(String isoDate) {
        System.out.println("Date provided -> " + isoDate);

        Instant instant = DateTimeFormatter.ISO_OFFSET_DATE_TIME.parse(isoDate, Instant::from);
        ZonedDateTime utcTimestamp = instant.atZone(ZoneOffset.UTC);
        int year = utcTimestamp.get(IsoFields.WEEK_BASED_YEAR);
        int weekOfYear = utcTimestamp.get(IsoFields.WEEK_OF_WEEK_BASED_YEAR);
        System.out.println("ZonedDateTime: Year " + year + " weekOfYear " + weekOfYear);

        // Force the Gregorian calendar with ISO rules and using UTC
        Calendar calendar = new GregorianCalendar();
        calendar.setFirstDayOfWeek(Calendar.MONDAY);
        calendar.setMinimalDaysInFirstWeek(4);
        calendar.setTimeZone(TimeZone.getTimeZone("UTC"));
        calendar.setTime(Date.from(instant));

        int calYear = calendar.getWeekYear();
        int calWeekOfYear = calendar.get(Calendar.WEEK_OF_YEAR);
        System.out.println("Calendar: Year " + calYear + " weekOfYear " + calWeekOfYear);
        System.out.println();
    }
}

输出：

Date provided -> 2049-01-02T03:48:00Z
ZonedDateTime: Year 2048 weekOfYear 53
Calendar: Year 2048 weekOfYear 53

Date provided -> 2049-12-31T03:48:00Z
ZonedDateTime: Year 2049 weekOfYear 52
Calendar: Year 2049 weekOfYear 52

这两个看起来都很好。

Answer 2

旧的Calendar - 确实能够实现Java-7以来的解决方案，因此我将其作为Jon Skeet的Java-8相关答案的补充：

String instantStr1 = "2049-01-02T03:48:00Z";
String instantStr2 = "2049-12-31T03:48:00Z";

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssXXX");
Date d1 = sdf.parse(instantStr1);
Date d2 = sdf.parse(instantStr2);

GregorianCalendar gcal = new GregorianCalendar();
gcal.setFirstDayOfWeek(Calendar.MONDAY);
gcal.setMinimalDaysInFirstWeek(4);

gcal.setTime(d1);
System.out.println(
    "Using Calendar API: Year " + gcal.getWeekYear() + " weekOfYear "
    + gcal.get(Calendar.WEEK_OF_YEAR)
); // Using Calendar API: Year 2048 weekOfYear 53

gcal.setTime(d2);
System.out.println(
    "Using Calendar API: Year " + gcal.getWeekYear() + " weekOfYear "
    + gcal.get(Calendar.WEEK_OF_YEAR)
); // Using Calendar API: Year 2049 weekOfYear 52

对于此API为标准的Android用户：自API级别24以来，方法getWeekYear()可用。

使用ZonedDateTime和Calendar API计算年度周问题

2 个答案: