java - 在时区之间转换纪元毫秒

Question

我得到一个纪元格式的数字。 Epoch 应该是 UTC，但我得到的是 PST 时区。所以我必须修复这个值。我该怎么做？

我一开始尝试的:

  // This number represents Tuesday, July 30, 2019 1:53:19 AM UTC, 
  // but it's supposed to represent PST.
  // The actual PST value for this date is going to be 1564476799000 
  // which is the same as Tuesday, July 30, 2019 8:53:19 AM UTC.
  // So I need to "pretend" that this value is actually PST 
  // and adjust it accordingly (including DST and friends).
  Long testDateLong = 1564451599000L;

  // These correctly assume that the instant is in UTC and adjust it to PST
  // which is not the real intention
  LocalDateTime pstL = LocalDateTime.ofInstant(Instant.ofEpochMilli(testDateLong), 
     ZoneId.of("America/Los_Angeles"));
  ZonedDateTime pstZ = ZonedDateTime.ofInstant(Instant.ofEpochMilli(testDateLong), 
     ZoneId.of("America/Los_Angeles"));

  System.out.println(pstL);
  System.out.println(pstZ);

  /*
   * Output:
   *
   * 2019-07-29T18:53:19
   * 2019-07-29T18:53:19-07:00[America/Los_Angeles]
   * 
   * Expected to see: 
   * 
   * 2019-07-30T01:53:19
   * 2019-07-30T01:53:19-07:00[America/Los_Angeles]
   * 
   */

可行的解决方案是将纪元值格式化为 UTC 格式的字符串，然后使用 PST 时区对其进行解析，如下所示:

  Long testDateLong = 1564451599000L;

  DateTimeFormatter formatterUTC = DateTimeFormatter
    .ofLocalizedDateTime(FormatStyle.SHORT)
    .withZone(ZoneId.of("Etc/UTC"));

  DateTimeFormatter formatterPST = DateTimeFormatter  
    .ofLocalizedDateTime(FormatStyle.SHORT)
    .withZone(ZoneId.of("America/Los_Angeles"));

  String utcString = formatterUTC.format(Instant.ofEpochMilli(testDateLong));

  Instant instant = Instant.from(formatterPST.parse(utcString));

  System.out.println(utcString);
  System.out.println(instant);
  System.out.println(instant.toEpochMilli());

  /*
   * Output:
   *
   * 7/30/19 1:53 AM
   * 2019-07-30T08:53:00Z
   * 1564476780000
   */

但是，对我来说这似乎是一个糟糕的解决方案(只是一种预感)。我想知道是否有比生成字符串并解析它更好的方法？

Answer 1

您可以使用UTC时区进行解析，然后更改时区

long testDateLong = 1564451599000L;
Instant ist = Instant.ofEpochMilli(testDateLong);

ZoneId zUTC = ZoneId.of("UTC");
ZoneId zLA = ZoneId.of("America/Los_Angeles");

ZonedDateTime zdt1 = LocalDateTime.ofInstant(ist, zUTC).atZone(zLA);
ZonedDateTime zdt2 = ZonedDateTime.ofInstant(ist, zUTC).withZoneSameLocal(zLA);

System.out.println(zdt1); // 2019-07-30T01:53:19-07:00[America/Los_Angeles]
System.out.println(zdt2); // 2019-07-30T01:53:19-07:00[America/Los_Angeles]