Convert Calendar date to LocalDate

Question

I decided to upgrade from 5.5 to Optaplanner 7.5 Nurseroster but have run into a number of silly issues. Below is one. The routine I previously used is below. Now however the new version requires LocalDate. I have an MySql database back-end and the users select the roster schedule planner via a calendar. Any suggestions will be appreciated.

int shiftDateSize = maxDayIndex + 1;
        List<ShiftDate> shiftDateList = new ArrayList<ShiftDate>(shiftDateSize);
        //shiftDateMap = new HashMap<String, ShiftDate>(shiftDateSize);
        long id = 0L;
        int dayIndex = 0;
        calendar.setTime(startDate);
        for (int i = 0; i < shiftDateSize; i++) {
            ShiftDate shiftDate = new ShiftDate();
            shiftDate.setId(id);
            shiftDate.setDayIndex(dayIndex);
            **String dateString = dateFormat.format(calendar.getTime());**
            shiftDate.setDateString(dateString);
            **shiftDate.setDayOfWeek(DayOfWeek.valueOfCalendar(calendar.get(Calendar.DAY_OF_WEEK)));**
            shiftDate.setShiftList(new ArrayList<Shift>());
            shiftDateList.add(shiftDate);
            shiftDateMap.put(dateString, shiftDate);
            id++;
            dayIndex++;
            calendar.add(Calendar.DAY_OF_YEAR, 1);
        }
        nurseRoster.setShiftDateList(shiftDateList);
    }

Possible duplicate of [Convert java.util.Date to java.time.LocalDate](https://stackoverflow.com/questions/21242110/convert-java-util-date-to-java-time-localdate) — daniu, Feb 26 '18 at 07:41

score 11 · Answer 1 · answered Jan 18 '19 at 09:58

I have tried the following code to get the LocalDate from Calendar

Calendar calendar = Calendar.getInstance();
TimeZone tz = calendar.getTimeZone();
ZoneId zid = tz == null ? ZoneId.systemDefault() : tz.toZoneId();
LocalDate localDate = LocalDateTime.ofInstant(calendar.toInstant(), zid).LocalDate();

or simply in one line:

LocalDate localDate = LocalDateTime.ofInstant(calendar.toInstant(), calendar.getTimeZone().toZoneId()).toLocalDate();

I have followed these steps from this link Convert Calendar to LocalDateTime

Volker Bach · Answer 2 · 2020-08-27T15:18:57.750

4

In Java 8 you can just do

LocalDateTime.ofInstant(cal.toInstant(), ZoneId.systemDefault())

edited Aug 27 '20 at 15:18

answered Aug 26 '20 at 10:43

Volker Bach

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score 3 · Answer 3 · edited Aug 06 '20 at 07:08

3

The following code probably works too.

Calendar cal = Calendar.getInstance();
Date input = cal.getTime();
LocalDate da = input.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();

This first gets the date in Date type and then converts it to LocalDate format as far as I know.

edited Aug 06 '20 at 07:08

Sven Hakvoort

3,033
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answered May 05 '19 at 14:28

dilanSachi

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11

Maksym Pecheniuk · Answer 4 · 2021-01-15T22:03:21.283

3

Java 9

import java.util.Calendar;
import java.time.LocalDate;
import java.time.ZoneId;

LocalDate.ofInstant(calendar.toInstant(), ZoneId.systemDefault());

edited Jan 15 '21 at 22:03

answered Oct 22 '20 at 13:16

Maksym Pecheniuk

1,695
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The `LocalDate.ofInstant()` method is only available since **Java 9**. – g00glen00b Jan 15 '21 at 10:23

score 0 · Answer 5 · answered Aug 27 '20 at 09:25

If you're reading the LocalDate(Time) from your SQL database and is the only API connection point (so Calendar isn't exposed anywhere), then don't use Calendar at all.

Use a Hibernate/JPA or JDBC version that supports LocalDate(Time) and read that directly from the database. They've been supporting it for years, but your hibernate/JPA or JDBC version connecting to MySQL might be older.

It is error prone to read a date from the database as a Calendar and then convert the Calendar into a LocalDate(Time). java.util.Calendar is inherently broken, that's why LocalDate(Time) was created. IIRC, errors included dependence on OS settings (timezone, DST rules, etc), making it's behavior machine dependent.

If Calendar is exposed in your API, then this answer won't work, of course.

Convert Calendar date to LocalDate

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