Java - date, format, time zones and Spring Boot defaults

Question

I have simple Java object with a date field:

@JsonFormat(pattern="yyyy-MM-dd HH:mm:ss")
private Date date;

When I investigate the date with debugger I see:

Wed Jun 14 00:00:00 BST 2017

But once I return it with Spring boot controller I get:

"date": "2017-06-13 23:00:00"

1. What's causing the difference?
2. Why Java treats the date as BST ?
3. Does Java Date class contain time-zone information or just plain timestamp in long format?
4. Is Spring boot using UTC format by default while serialising DTOs to JSON?

Answer 1

java.util.Date has no timezone information (only the long timestamp), but it uses the system's default timezone in the toString() method - you can find more info about this here (as already suggested in the comments).

Just check the value of TimeZone.getDefault() . It'll probably be Europe/London - as London in now in summer time, the short name (used by Date.toString() ) of this timezone is BST .

As your output suggests, Spring is probably using UTC (as 2017-06-13 23:00:00 in UTC is 2017-06-14 00:00:00 in BST ).