CODEWITHSUNDEEP
javadatelocaltime
Stanko
Stanko

Reputation: 4465

LocalTime from Date

I'm trying to convert a Date instance to a LocalTime instance.

// Create the Date
Date date = format.parse("2011-02-18 05:00:00.0");    

// Convert to Calendar
Calendar cal = Calendar.getInstance();
cal.setTime(date);

// Convert Calendar to LocalTime
Instant instant = Instant.ofEpochMilli(cal.getTimeInMillis());
LocalTime convert = LocalDateTime.ofInstant(instant, ZoneId.systemDefault()).toLocalTime();

I don't get a compiler error but the LocalTime instance values are wrong.

I think it does not work because Date stores time in fasttime instead of cdate.

I'm using JDK version 1.8.

Upvotes: 20

Views: 46779

Answers (4)

johanwannheden
johanwannheden

Reputation: 952

This is also quite simple:

LocalTime time = LocalDateTime.ofInstant(new Date().toInstant(),
    ZoneId.systemDefault()).toLocalTime();

Upvotes: 24

Basil Bourque
Basil Bourque

Reputation: 338171

The accepted Answer by Jon Skeet is correct. This Answer expands on those ideas.

Avoid legacy date-time classes

Some of the other Answers, and the Question, mix the old legacy date-time classes with the new. That is unnecessary and bad practice. The whole point of the java.time classes is to replace the troublesome and confusing old classes.

  • You do not need java.util.Date.
  • You do not need java.util.Calendar.

LocalDateTime

Your input string lacks any information about offset-from-UTC or time zone. So we parse it as a LocalDateTime object.

To parse, we replace the SPACE in the middle with a T to comply with the ISO 8601 standard for date-time formats.

String input = "2011-02-18 05:00:00.0".replace( " " , "T" );
LocalDateTime ldt = LocalDateTime.parse( input );

LocalTime

To focus on the time-of-day without the date, ask for a LocalTime.

LocalTime lt = ldt.toLocalTime();

ZonedDateTime

Note that none of this are actual moments, not a point on the timeline. Without the context of an offset-from-UTC or a time zone, we do not know if you meant 5 AM in Auckland NZ or 5 AM in Kolkata IN or 5 AM in Paris France or 5 AM in Montréal Québec. Each of those would be very different moments in time.

If by context you do know for certain the intended time zone, apply it. Apply a ZoneId to get a ZonedDateTime.

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = ldt.atZone( z );

From there, ask for the LocalTime if desired.

LocalTime lt = zdt.toLocalTime();

Instant

If you want to see that same moment in UTC, extract an Instant. The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

Generally best to focus on UTC in much of your business logic, logging, data storage, and data exchange. Learn to think of UTC as “The One True Time”.

Instant instant = zdt.toInstant();  // Same moment, shifted to UTC.

Upvotes: 3

user4624062
user4624062

Reputation:

Try this

    String datestring = "2011-02-18 05:00:00.0";
    SimpleDateFormat dt = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");//take a look at MM
    Date date = dt.parse(datestring );
    Instant instant = Instant.ofEpochMilli(date.getTime());
    LocalTime res = LocalDateTime.ofInstant(instant, ZoneId.systemDefault()).toLocalTime();

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1499770

Your input is effectively a LocalDateTime. It would be much simpler to simply parse that to a LocalDateTime and then get the LocalTime from that. No time zones to worry about, no somewhat-legacy classes (avoid Date and Calendar where possible...)

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

public class Test {

    public static void main(String[] args) {
        DateTimeFormatter formatter =
            DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.S", Locale.US);

        String text = "2011-02-18 05:00:00.0";
        LocalDateTime localDateTime = LocalDateTime.parse(text, formatter);
        LocalTime localTime = localDateTime.toLocalTime();
        System.out.println(localTime);
    }
}

Upvotes: 12

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