如何将字符串 (HH:mm) 设置为当前日期的 UTC 时间并将其转换为本地时间

Question

我需要将 (HH:mm) 格式的字符串转换为本地时区，该字符串应该是 UTC 时间。如何将当前日期添加到字符串并将其转换为当地时间。我尝试过使用日历String utcTimeString = "06:00";SimpleDateFormat sdf = new SimpleDateFormat("HH:mm", Locale.getDefault());sdf.setTimeZone(TimeZone.getTimeZone("UTC"));Calendar now = Calendar.getInstance(Locale.getDefault());now.setTime(sdf.parse(utcTimeString));

Answer 1

强烈建议您使用现代 API 来获取日期、时间、时区、偏移量、日历等：

java.time

这样做，非常容易

1. 解析你收到的时间

2. 获取当前日期和

3. 将它们组合成具有特定时区的日期时间表示

看这个小例子：

public static void main(String[] args) {

    // create a time object from the String

    LocalTime localTime = LocalTime.parse("06:00", DateTimeFormatter.ofPattern("HH:mm"));

    // print it once in an ISO format

    System.out.println(localTime.format(DateTimeFormatter.ISO_TIME));

    // receive the date of today

    LocalDate today = LocalDate.now();

    // then use the date and the time object to create a zone-aware datetime object

    ZonedDateTime zdt = LocalDateTime.of(today, localTime).atZone(ZoneId.of("UTC"));

    // print it

    System.out.println(zdt.format(DateTimeFormatter.ISO_ZONED_DATE_TIME));

}

输出是

06:00:00

2019-11-04T06:00:00Z[UTC]

您可以根据需要使用不同的DateTimeFormatters 进行格式化。

Answer 2

尝试如下所示。

public String getDateTimeInUTC(String yourTime){ 

    Calendar cal = Calendar.getInstance();

    SimpleDateFormat currentDate= new SimpleDateFormat("MMM dd, yyyy ");

    String currentDateTime = currentDate.format(cal.getTime())+yourTime; // here concate your time with current date.

    System.out.println("Current date with given time: "+currentDateTime);

    SimpleDateFormat df = new SimpleDateFormat("MMM dd, yyyy HH:mm", Locale.ENGLISH);

    df.setTimeZone(TimeZone.getTimeZone("UTC"));

    Date date = null;

    try {

       date = df.parse(currentDateTime);

    } catch (ParseException e) {

       e.printStackTrace();

    }

    df.setTimeZone(TimeZone.getDefault());

    String formattedDate = df.format(date);

    return formattedDate;

}

getDateTimeInUTC像下面这样调用

String strTime = "12:10"; // your string time in HH:mm format

String finalDateTime = getDateTimeInUTC(strTime);

System.out.println("Final date-time in UTC: "+finalDateTime);

输出：

Current date with  given time: Nov 04, 2019 12:10

Final date-time in UTC: Nov 04, 2019 18:10

Answer 3

您可以查看一下：

Calendar calendar = Calendar.getInstance();

calendar.setTime(new Date());

//change the format according to your need

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");

//Here you say to java the initial timezone. This is the secret

sdf.setTimeZone(TimeZone.getTimeZone("UTC"));

//Will print in UTC

System.out.println(sdf.format(calendar.getTime()));    

//Here you set to your timezone

sdf.setTimeZone(TimeZone.getDefault());

//Will print on your default Timezone

System.out.println(sdf.format(calendar.getTime()));