How to change Date and Time format in Java

i know this is a simple question but what date and time format should i use to show this output.

2019-02-06T3:26:40+08:00

I’m using java.time.
I use LocalDateTime but it only outputs 2020-10-06T16:40:04 and didn’t have the +08:00.

I only use this:

LocalDateTime myObj = LocalDateTime.now();
System.out.println(myObj);

I don’t know how to format like the example above.

tl;dr

// take the current time at a specific offset from UTC
OffsetDateTime offsetDateTime = OffsetDateTime.now(ZoneOffset.ofHours(8));
// define an output pattern
String pattern = "uuu-MM-dd'T'H:mm:ssxxx";
// and print some result using a formatter with the pattern defined
System.out.println("Formatted with pattern "
                   + pattern 
                   + ": " 
                   + offsetDateTime.format(DateTimeFormatter.ofPattern(pattern)));

will output something similar to this line (time may/will differ, at least):

Formatted with pattern uuu-MM-dd'T'H:mm:ssxxx: 2020-10-06T17:02:49+08:00

Problem with your code:

1. Your code example was given in a comment, not in the question
   (this is not a functional problem related to Java but still a problem here, you can edit that)

2. You are currently using a LocalDateTime, which does not hold any information about an offset or a time zone

3. You are not defining a desired output pattern but (implicitly) invoking the toString() method of the LocalDateTime by just printing the instance in the following code (the one from your comment):

LocalDateTime myObj = LocalDateTime.now();
System.out.println(myObj);

outputs a String like 2020-10-06T16:40:04 without the desired +08:00.

<del>

You can create an OffsetDateTime using an instance of LocalDateTime and a desired ZoneOffset, like

LocalDateTime localNow = LocalDateTime.now();
OffsetDateTime offsetDateTime = OffsetDateTime.of(localNow, ZoneOffset.ofHours(8));
System.out.println(offsetDateTime.format(DateTimeFormatter.ISO_OFFSET_DATE_TIME));

which also uses a predefined output pattern, which slightly differs from your desired one (fractions-of-second is displayed between seconds and the offset).

</del>

But please note that this approach may return an incorrect point in time under certain circumstances (see the comment by @OleV.V. below this answer).

If you are sure every system that code is running on has and will always have a time zone setting with an offset of +08:00, you can use OffsetDateTime.now() without adding a ZoneOffset explicitly or use the system default exlicitly by OffsetDateTime nowExplicitSystemOffset = OffsetDateTime.now(ZoneId.systemDefault());.

I recommend having a look at Trail: Date Time (The Java Tutorials).

OffsetDateTime

Use OffsetDateTime instead of LocalDateTime:

	OffsetDateTime myObj = OffsetDateTime.now(ZoneId.systemDefault());
	System.out.println(myObj);

I ran this just now in Asia/Hong_Kong time zone. The output was:

> 2020-10-07T03:25:03.254761+08:00

The format you asked for is ISO 8601. The classes of java,time generally print ISO 8601 format from their toString methods. A LocalDateTime object doesn’t include any offset or time zone. An OffsetDateTime, as the name says, does include a UTC offset such as +08:00 and therefore also prints it from toString().

It is not strictly necessary to pass ZoneId.systemDefault() as argument to now(). You will get the same result if you leave it out. Since the current time is time zone dependent, I always prefer to make it explicit which time zone I am using, so I and the reader both know that I have made a conscious choice.

Links

• Oracle tutorial: Date Time explaining how to use java.time.
• Wikipedia article: ISO 8601

public class CurrentDateTimeExample2 {
    public static void main(String[] args) {
        System.out.println(java.time.Clock.systemUTC().instant()); 
    }
}

Example output:

> 2020-10-07T20:50:11.758582Z