Java将字符串yyyy-MM-dd HH：mm：ss转换为加拿大/东部时区的时间戳

Question

I have to get DateTime with using TimeZone and then get Timestamp from that DateTime

My Code is give below :

DateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date dt = new Date();
String currentTime = formatter.format(dt);
System.out.println("currentTime>>>>" + currentTime);

DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
format.setTimeZone(TimeZone.getTimeZone("Canada/Eastern"));
Date parsedDate = format.parse(currentTime);
System.out.println("parsedDate>>>>" + parsedDate);
Timestamp timestamp = new Timestamp(parsedDate.getTime());
System.out.println("timestamp>>>>>>" + timestamp);

Problem is that I am not getting right datetime of Canada/Eastern TimeZone in timestamp.

I am getting the below time

currentTime>>>>2016-11-09 15:17:09
parsedDate>>>>Thu Nov 10 01:47:09 IST 2016
timestamp>>>>>>2016-11-10 01:47:09.0

Indian time is correct : 2016-11-09 15:17:09
When I parse it to Canada/Eastern it shows : Thu Nov 10 01:47:09 IST 2016

But eastern canada time is 04:50:21 EST Wednesday, 9 November 2016

I am using Java with Eclipse Mars 1.

Answer 1

Timestamp is unique and same every where in all timezones, which is value of new Date() in millis. What you are looking for here is formatted time of given timestamp (dt in above example.).

Date dt = new Date();
DateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

System.out.println("IST time: " + format.format(dt));

format.setTimeZone(TimeZone.getTimeZone("Canada/Eastern"));

String parsedDate = format.format(dt);

System.out.println("Canada Time: " + parsedDate);

Output: IST time: 2016-11-09 16:33:22 Canada Time: 2016-11-09 06:03:22

Answer 2

tl;dr

Instant.now()
       .atZone( ZoneId.of( "America/Toronto" ) )

No parsing! Do not parse to adjust time zone.

Avoid the troublesome old classes: java.text.SimpleDateFormat , java.util.Date , java.util.TimeZone .

java.time

You are using troublesome old date-time classes, now legacy, supplanted by the java.time classes.

Instant

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

Instant instant = Instant.now();

2016-11-10T04:52:02.586Z

Time zone

You can adjust this Instant into a time zone by applying a ZoneId to get a ZonedDateTime .

Do not parse as a way to adjust time zone! perhaps you are conflating a date-time object with a string that might represent its value. A date-time object can generate a string, and can parse a string, but the string is always distinct and separate from the date-time object.

Specify a proper time zone name in the format of continent/region , such as America/Montreal , Africa/Casablanca , or Pacific/Auckland . Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

Furthermore, your Canada/Eastern zone is actually just an alias for the real zone of America/Toronto .

ZoneId z = ZoneId.of( "America/Toronto" );
ZonedDateTime zdt = instant.atZone( z );

2016-11-09T23:52:02.586-05:00[America/Toronto]

You could adjust into India time as well.

ZoneId zKolkata = ZoneId.of( "Asia/Kolkata" );
ZonedDateTime zdtKolkata = instant.atZone( zKolkata );

2016-11-10T10:22:02.586+05:30[Asia/Kolkata]

Dump to console.

System.out.println( "instant: " + instant );
System.out.println( "zdt: " + zdt );
System.out.println( "zdtKolkata: " + zdtKolkata );

instant: 2016-11-10T04:52:02.586Z

zdt: 2016-11-09T23:52:02.586-05:00[America/Toronto]

zdtKolkata: 2016-11-10T10:22:02.586+05:30[Asia/Kolkata]

See live code in IdeOne.com .

Database

By Timestamp I assume you meant java.sql.Timestamp . That class is now outmoded by the java.time classes, if you have a JDBC driver that complies with JDBC 4.2 or later. Just pass the Instant object to PreparedStatement::setObject . Fetch via ResultSet::getObject .

myPreparedStatement.setObject( … , instant );

If your JDBC driver does not comply, fall back to converting to java.sql.Timestamp . But minimize use of that class, only for talking to the database. Immediately convert back into java.time. Do not attempt business logic with Timestamp .

java.sql.Timestamp ts = java.sql.Timestamp.from( instant );

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to java.time.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

Where to obtain the java.time classes?

• Java SE 8 and SE 9 and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
  • See How to use… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .

Answer 3

You can set the TimeZone based on GMT. We know that Canada time is GMT-5 , so you can get the current Canada time like this:

    TimeZone tz = TimeZone.getTimeZone("GMT-5");
    Calendar c = Calendar.getInstance(tz);
    SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.CANADA);

    dateFormat.setTimeZone(tz);

    System.out.println(dateFormat.format(c.getTime()));

Output: 2016-11-09 06:08:47

You need to explicitly use DateFormat.setTimeZone() to print the Date in the desired timezone. If you don't do this, the c.getTime() result will be your zone current time.

Answer 4

A Timestamp doesn't have a time zone in Java, it only represents a moment in time based on a number of milliseconds elapsed since a reference point, the epoch.

So it seems to me that you want your Timestamp to point to the current instant, which would be written very simply:

//with Java 8
Timestamp ts = Timestamp.from(Instant.now());

//or prior to Java 8:
Timestamp ts = new Timestamp(new Date().getTime());