Java 将日期时间转换为给定格式

Question

I need some help to convert the given local date time value (or util date) to one of the below formats with (ASIA/COLOMBO) time zone. Here are the formats (from one-signal API).

"Thu Sep 24 2015 14:00:00 GMT-0700 (PDT)"

"September 24th 2015, 2:00:00 pm UTC-07:00"

"2015-09-24 14:00:00 GMT-0700"

"Sept 24 2015 14:00:00 GMT-0700"

"Thu Sep 24 2015 14:00:00 GMT-0700 (Pacific Daylight Time)"

Thanks.

Answer 1

ZonedDateTime

Instantiate a date, time, and zone into a ZonedDateTime object.

LocalDate ld = LocalDate.of( 2015 , Month.SEPTEMBER , 24 ) ;
LocalTime lt = LocalTime.of( 14 , 0 ) ;
ZoneId z = ZoneId.of( "Asia/Colombo" ) ;
ZonedDateTime zdt = ZonedDateTime.of( ld , lt , z ) ;

If given a java.util.Date object, convert to a Instant .

Instant instant = myJavaUtilDate.toInstant() ;

Apply a zone to move from UTC.

ZoneId z = ZoneId.of( "Asia/Colombo" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;

To produce text in your desired formats, use DateTimeFormatter class. This has been addressed many many times already on Stack Overflow. So search for that class name to learn more.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "uuuu-MM-dd HH:mm:ss OOOO" ) ;
String output = zdt.format( f ) ;

2015-09-24 14:00:00 GMT+05:30

ISO 8601

Those formats you showed are all terrible choices. When exchanging date-time values as text, use standard ISO 8601 formats. The standard formats are designed to be easy to parse by machine, and easy to read by humans across cultures.

The java.time classes use ISO 8601 formats by default when parsing/generating strings.

Answer 2

The java.time classes were introduced in 1.8 and allows for more flexible and concise code.

Instant now = Instant.now();
ZonedDateTime dateTime = now.atZone(ZoneId.of("Asia/Colombo"));
DateTimeFormatter format = DateTimeFormatter.ofPattern("E M d u HH:mm:ss OOOO (z)");

// Using a format to convert at Temporal to a string
String formattedDate = format.format(dateTime);

// Using a format to convert a string to a Instant
Instant parsedDate = Instant.from(format.parse(formattedDate));

You can specify your date's format using DateTimeFormatter.ofPattern or one of the many constants defined in DateTimeFormatter. The pattern I created matches your first example.

The old method

These classes are yet to be deprecated and I find to be more straight forward for simple cases than the modern method.

java.text.SimpleDateFormat; It can handle going to and from a String and java.util.Date Object.

SimpleDateFormat format = new SimpleDateFormat("EEE MMM dd yyyy HH:mm:ss Z (z)");
format.setTimeZone(TimeZone.getTimeZone("Asia/Colombo"));
// Note that the current date and time will be used when instantiating a new Date object.
String formattedDate = format.format(new Date());

try {
    Date parsedDate = format.parse(formattedDate);
} catch (ParseException exception) {
    // Handle malformed date
}

You will just have to create the pattern for any format you'd like to use.

EEE MMM dd yyyy HH:mm:ss Z (z) = Thu Sep 24 2015 14:00:00 GMT-0700 (PDT)