在给出周数，工作日和年份的Java中获取日期

Question

Given Week of the year, the week day and the year, how can we get the Date in Java?

With Jodatime, I tried the following:

DateTime dt = new DateTime();
dt.withYear(year);
dt.withWeekOfWeekyear(weekOfYear);
dt.withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));

But it gets the current Date!

Answer 1

JodaTime returns a changed copy, so do:

DateTime dt = new DateTime()
    .withWeekyear(year)
    .withWeekOfWeekyear(weekOfYear)
    .withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));

And this should work as expected.

Answer 2

The accepted answer has bug. .withYear(year) should be withWeekyear(year) . @Neet please update it.

Answer 3

You need to reassign the date afterwards! the dt.with*() methods simply make a copy of the date.

try

DateTime dt = new DateTime();
dt = dt.withYear(year);
dt = dt.withWeekOfWeekyear(weekOfYear);
dt = dt.withDayOfWeek(weekDay);
DateTimeFormatter dateTimeFormatter = DateTimeFormat.forPattern("yyMMdd");
System.out.println(dateTimeFormatter.print(dt));

Answer 4

We can also use this native java code using Calendar class:

    SimpleDateFormat sdf = new SimpleDateFormat("MM dd yyyy");
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.WEEK_OF_YEAR, 23);
    cal.set(Calendar.DAY_OF_WEEK, 3);
    cal.set(Calendar.YEAR,2013);
    System.out.println(sdf.format(cal.getTime()));

Answer 5

Here is a simple example of how to do it without JodaTime:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Snippet {
    public static void main(String args[]) {
        String year = "2013";
        String week_of_year = "46";
        String day_of_week = "4";
        String yearweekday = year + week_of_year + day_of_week;
        SimpleDateFormat sdf = new SimpleDateFormat("yyyywwu");
        Date date = null;
        try {
            date = sdf.parse(yearweekday);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        System.out.println(date);
    }
}

Good luck!

Answer 6

tl;dr

YearWeek.of( 2017 , 1 )
        .atDay( DayOfWeek.TUESDAY ) 
        .format( DateTimeFormatter.ofPattern( "uuMMdd" ) ) 

“Week” ambiguous

The word 'week' is ambiguous. Do you mean week number 1 contains January 1? Or week number 1 contains the first of a particular day of year such as Sunday or Monday?

Or do you mean a standard ISO 8601 week ? To quote from YearWeek doc :

ISO-8601 defines the week as always starting with Monday. The first week is the week which contains the first Thursday of the calendar year. As such, the week-based-year used in this class does not align with the calendar year.

java.time

The modern approach uses the java.time classes.

• The troublesome old date-time classes such as java.util.Date , java.util.Calendar , and java.text.SimpleTextFormat are now legacy , supplanted by the java.time classes.
• The Joda-Time project is now in maintenance mode , with the team advising migration to the java.time classes.

ThreeTen-Extra

The ThreeTen-Extra project extends java.time with additional functionality. This includes a handy YearWeek class, just what we need for this Question.

Specify your week-based year number and your week number.

YearWeek yw = YearWeek.of( 2017 , 1 ) ; 

The LocalDate class represents a date-only value without time-of-day and without time zone.

You can ask the YearWeek object to determine the date of a day contained within its week. Specify a DayOfWeek enum object. Note that a DayOfWeek is an object rather than a mere integer or string, providing for type-safety and valid values.

LocalDate ld = yw.atDay( DayOfWeek.TUESDAY ) ; 

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .