I have a situation where I need to convert one Java date time format into another but have been having just a bear of a time doing so. Been searching for solutions a long time and have tried many things that have just not worked but I'm at my wits end :(.

I have to convert from yyyy-MM-dd'T'HH:mm:ss to MM/dd/yyyy HH:mm:ss

This is the last thing I've tried, but alas it has no effect at all at transforming the pattern:

private Instant convertInstantFormat(Instant incomingDate) {
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern(AUTH_DATE_PATTERN)
        .withZone(ZoneId.systemDefault());
    return Instant.parse(formatter.format(incomingDate));
}

Where

AUTH_DATE_PATTERN = "MM/dd/yyyy HH:mm:ss";

incomingDate = 2021-10-22T06:39:13Z and outgoing date = 2021-10-22T06:39:13Z

I'm sure this is probably just the most naive attempt. I've tried standardizing the date format and then reformatting, but no go.

I'm just sort of out of steam. As always, any and all help from this incredible community is tremendously appreciated!

UPDATE

I just wanted to point out that the input and output to this method are of type "Instant." Apologies for not making this clear initially.

CodePudding user response：

I have to convert from yyyy-MM-dd'T'HH:mm:ss to MM/dd/yyyy HH:mm:ss

Your incoming date time format is ISO_LOCAL_DATE_TIME.

String datetime = "2021-12-16T16:22:34";
LocalDateTime source = LocalDateTime.parse(datetime,DateTimeFormatter.ISO_LOCAL_DATE_TIME);

// desired output format
String AUTH_DATE_PATTERN = "MM/dd/yyyy HH:mm:ss";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(AUTH_DATE_PATTERN);
String output = source.format(formatter);
System.out.println(output);

prints

12/16/2021 16:22:34

If your incoming date is 2021-10-22T06:39:13Z that is a zoned date time and can be parsed-from/formatted-to using DateTimeFormatter.ISO_ZONED_DATE_TIME.

CodePudding user response：

Append timezone 'z' info at the end of the format pattern otherwise parsing throws an exception.

Here's a working example.

Unit Test (Passing)

import org.junit.jupiter.api.Test;
import static org.assertj.core.api.Assertions.assertThat;

class DateFormatConverterTest {

    @Test
    void convertDate() {
        final String incomingDate = "2021-10-22T06:39:13Z";
        final String expectedOutgoingDate = "2021/10/22T06:39:13Z";

        String actualOutgoingDate = new DateFormatConverter().convertDate(incomingDate);
        assertThat(actualOutgoingDate).isEqualTo(expectedOutgoingDate);
    }

}

Implementation

import java.time.format.DateTimeFormatter;

public class DateFormatConverter {

    private static final DateTimeFormatter INCOMING_DATE_TIME_FORMAT = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssz");
    private static final DateTimeFormatter OUTGOING_DATE_TIME_FORMAT = DateTimeFormatter.ofPattern("yyyy/MM/dd'T'HH:mm:ssz");

    String convertDate(String incoming) {
        return OUTGOING_DATE_TIME_FORMAT.format(INCOMING_DATE_TIME_FORMAT.parse(incoming));
    }

}

CodePudding user response：

tl;dr

Instant                           // Represents a point on the time line. 
.parse( "2021-10-22T06:39:13Z" )  // Returns an `Instant` object. By default, parses text in standard ISO 8601 for at where `Z` means offset of zero.
.atOffset( ZoneOffset.UTC )       // Returns an `OffsetDateTime` object. 
.format(
    DateTimeFormatter.ofPattern( "MM/dd/uuuu HH:mm:ss" )
)                                 // Returns a `String` object.

See this code run live at IdeOne.com.

10/22/2021 06:39:13

Details

You said:

incomingDate = 2021-10-22T06:39:13Z

Your formatting pattern fails to match your input string.

Your input string happens to comply with the ISO 8691 format used by default in Instant.parse. So no need to specify a formatting pattern.

Instant instant = Instant.parse( "2021-10-22T06:39:13Z" ) ;

The Z on the end means an offset of zero hours-minutes-seconds from the prime meridian of UTC.

You asked to generate text representing that moment in the format of MM/dd/yyyy HH:mm:ss. I recommend including an indicator of the offset or time zone. But it you insist on omitting that, read on.

Convert from the basic class Instant to the more flexible OffsetDateTime class.

OffsetDateTime odt = instant.atOffset( ZoneOffset.UTC ) ;

Specify your formatting pattern.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "MM/dd/uuuu HH:mm:ss" ) ;

Generate your desired text.

String output = odt.format( f ) ;

To learn more, search Stack Overflow. These topics have already been addressed many times.