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I want to rename my file name according to yyyy_[DayOfTheYear]. The day of the year should be in 3 digits always. For example, 01-01-2021 -> 2021_001 ; 31-01-2021 -> 2021_031 ; 31-12-2021 -> 2021_365 Is there any predefined method to get the 3 digits in Java?

Shivam Thakur
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  • There are two separate problems here - retrieving the day of year, and padding 0s to the left. Which one are you asking about? – Sweeper Feb 03 '21 at 12:20
  • @Sweeper padding 0s to the left is obviously like the last option. Getting the day is not difficult but my question was for getting the day in 3 digits by default without any padding. – Shivam Thakur Feb 03 '21 at 12:28

1 Answers1

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Check LocalDate::getDayOfYear().

The instance of LocalDate may be formatted using String.format or using DateTimeFormatter::ISO_ORDINAL_DATE. The latter allows to get year and day of year, however, these values are delimited with '-', which can be replaced if necessary.

Example:

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;

public class MyClass {
    public static void main(String args[]) {
      LocalDate today = LocalDate.now();
      
      DateTimeFormatter yearDayOfYear = DateTimeFormatter.ISO_ORDINAL_DATE;

      System.out.printf("%s -> %4d_%03d%n", today, today.getYear(), today.getDayOfYear());
      System.out.printf("%s -> %s%n", today, today.format(yearDayOfYear).replace('-', '_'));
    }
}

Output:

2021-02-03 -> 2021_034
2021-02-03 -> 2021_034
Nowhere Man
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