I am looking to understand why this code is giving me different results.

I want to format 2022-10-12T00:00:00.000Z into yyyy-MM-dd format.

• Result when I run it online in Java IDE: 2022-10-12
• But on my own computer the result is: 2022-10-11

String date = "2022-10-12T00:00:00.000Z";
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
TemporalAccessor ta = DateTimeFormatter.ISO_INSTANT.parse(date);
Instant i = Instant.from(ta);
Date d = Date.from(i);
dateFormat.format(d);

CodePudding user response：

If the online IDE is running in a different time zone than you, it might be 10-12 in one time zone and still 10-11 in another. You have specified Z as the time zone of the input, but you have not specified the time zone used in formatting the date.

CodePudding user response：

A couple of important points:

1. The java.util date-time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern date-time API.
2. SimpleDateFormat does not have a way to specify a time-zone in the pattern. The way to specify a time-zone with SimpleDateFormat is by calling SimpleDateFormat#setTimeZone(java.util.TimeZone). Without setting time-zone explicitly, SimpleDateFormat uses the system time-zone. You could get the desired result had you done the following

    dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
    dateFormat.format(d);

Demo with java.time API:

import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;

public class Main {
    public static void main(String[] args) {
        String strDate = "2022-10-12T00:00:00.000Z";

        // Parse the given text into an OffsetDateTime and format it
        String desiredString = OffsetDateTime.parse(strDate)
                .format(DateTimeFormatter.ISO_LOCAL_DATE);

        System.out.println(desiredString);
    }
}

Output:

2022-10-12

Learn more about the modern Date-Time API from Trail: Date Time.

CodePudding user response：

It may be that Date/SimpleDateFormat don’t support time zone. You can try using the java.time package:

LocalDate.now()
DateTimeFormatter.ofPattern("yyyy-MM-dd").format(LocalDate.now())