为包含00:00:00的字符串添加小时数

Question

I am going to send the dateTime variable to an API which requires a String with the time and date in it. But I noticed that there is a time difference, because when I send that variable, it ends up with two hours added on it. So I need to add 2 hours to the time variable.

I tried splitting the time variable, parsed the first element to an int and added 2, and then formatted to a String and so forth, but this seems extremely unnecessarily long. Is there any easier way? I've tried to figure out how to work with time objects and setting the date and time, but I only know how to set to the current time, which I do not want to do. The code below contains the values needed.

String date = "2019-05-09";
String time = "10:00:00";
String dateTime = (date + "T" + time + "Z");

Answer 1

Is there any easier way?

Yes, use the modern java.time classes.

Apparently you are trying to communicate a moment of 10 AM on that date in UTC. The Z in your example code means UTC, pronounced “Zulu”.

To do so, use OffsetDateTime with an offset specified by the ZoneOffset.UTC constant.

LocalDate ld = LocalDate.parse( "2019-05-09" ) ;
LocalTime lt = LocalTime.parse( "10:00:00" ) ;
OffsetDateTime odt = OffsetDateTime.of( ld , lt , ZoneOffset.UTC ) ;

Apparently you want to send this value as a string in standard ISO 8601 format. Those formats are used by default in the java.time classes when parsing/generating strings.

String output = odt.toString() ;

You do not explain exactly how or where this 2 hour discrepancy appears. I would guess that you are seeing a result after an adjustment has been made from UTC to some time zone. If so, you have no problem .

If two people are telephoning, in time zones two hours apart, if they look up simultaneously to read the current time from the clock on their respective wall, one person will see 10 AM while the other sees 12 noon. Same moment, same point on the timeline, different wall-clock time.

You can verify this by applying a ZoneId for the suspected time zone, to see the wall-clock time value in the resulting ZonedDateTime object.

ZoneId z = ZoneId.of( "Europe/Paris" ) ;
ZonedDateTime zdt = odt.atZoneSameInstant( z ) ;  // Same moment, same point on the timeline, different wall-click time. 

Answer 2

This method might give you helpful hints. Output is: 2019-05-09 16:05

public static void main(String[] args) {

LocalDateTime localDateTime = LocalDateTime.now().plusHours(2);
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
System.out.println(localDateTime.format(formatter));
}