Illegal date format Java

Question

I’m trying to send a parameter to an API that requires a date-time like >=2014-01-02T08:12:32Z (from the documentation).

To have this format, for what I know, I have to use something like this:

new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX").format(when)

But I’m getting an error from the API saying that the date is not valid.

The generated date is the following:

2021-05-21T20:08:14+02

For what I can see, the only format difference is the trailing Z that I thought was the timezone... what am I missing? What should I do to get that trailing "Z"?

Answer 1

tl;dr

java.time.Instant         // Represent a moment as seen with an offset-from-UTC of zero hours-minutes-seconds.
.now()                    // Capture the current moment.
.truncatedTo(             // Lop off any fractional second.
    ChronoUnit.SECONDS    // An enum specifying the granularity of truncation.
)                         // Returns another `Instant` object rather than altering the original, per immutable-objects pattern.
.toString()               // Generate text representing the content of this object, using standard ISO 8601 format.

2021-05-25T01:05:03Z

Details

Avoid legacy date-time classes

You are using terrible date-time classes that were supplanted years ago by the modern java.time classes.

java.time

To capture the current moment as seen in UTC, use Instant.now.

So:

Instant.now().toString()

… is all you need.

See this code run live at IdeOne.com.

2021-05-25T01:05:03.208937Z

The Z on the end means an offset-from-UTC of zero hours-minutes-seconds. Pronounced “Zulu”. Equivalent to +00:00.

Truncation

If you just want the whole seconds only, and drop the fractional second, truncate.

  Instant.now().truncatedTo( ChronoUnit.SECONDS ).toString() 

See the code run live at IdeOne.com.

2021-05-25T01:05:03Z

Answer 2

Z is the time zone, but perhaps the recipient only supports Z. It is not unheard of.

To get the time adjusted, simply specify the desired time zone in the formatter.

// Simulate question's time zone
TimeZone.setDefault(TimeZone.getTimeZone("GMT+02"));

// Set `when` and show it for proof
Date when = Date.from(OffsetDateTime.parse("2021-05-21T20:08:14+02").toInstant());
System.out.println(when);
// Output: Fri May 21 20:08:14 GMT+02:00 2021

// See that question code generates same output
System.out.println(new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX").format(when));
// Output: 2021-05-21T20:08:14+02

// Add desired time zone to formatter
SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX");
fmt.setTimeZone(TimeZone.getTimeZone("UTC"));
System.out.println(fmt.format(when));
// Output: 2021-05-21T18:08:14Z   (note how hour was changed from 20 to 18)

---

I would however recommend you start using the Time API added in Java 8.

// Set `when` and show it for proof
OffsetDateTime when = OffsetDateTime.parse("2021-05-21T20:08:14+02");
System.out.println(when);
// Output: 2021-05-21T20:08:14+02:00

// See same output as question
System.out.println(when.format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssX")));
// Output: 2021-05-21T20:08:14+02

// Option 1: Add desired time zone to formatter
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ssX")
        .withZone(ZoneOffset.UTC);
System.out.println(fmt.format(when));
// Output: 2021-05-21T18:08:14Z

// Option 2: Change time zone of value
OffsetDateTime whenUTC = when.atZoneSameInstant(ZoneOffset.UTC).toOffsetDateTime();
System.out.println(whenUTC);
// Output: 2021-05-21T18:08:14Z

Answer 3

You can see an example here https://howtodoinjava.com/java/date-time/java-date-formatting/

import java.text.SimpleDateFormat;
import java.util.Date;
 
public class JavaDateValidations 
{
    public static final String TIMESTAMP_PATTERN 
                            = "yyyy-MM-ddTHH:mm:ss"; 
 
    public static void main(String[] args) 
    {
        SimpleDateFormat sdf = new SimpleDateFormat(TIMESTAMP_PATTERN);
         
        Date date = new Date();
         
        String formattedDate = sdf.format(date);
        System.out.println(formattedDate);      //2020-05-09T00:32:28
    }
}