java - 如何从 TemporalAccessor 获取 ZoneId、LocalDateTime 和 Instant

Question

我正在使用下面的代码来解析日期字符串:

    String time = "2 Jun 2019 03:51:17 PM ACST";
    String pattern = "d MMM yyyy hh:mm:ss a z"; // z detects the time zone (ACST here)
    DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);

 // ZonedDateTime localDateTime = LocalDateTime.from(formatter.parse(time)).atZone(ZoneId.of("Australia/Adelaide"));
 // localDateTime.toInstant().toEpochMilli();

当我通过调试检查时，formatter.parse(time) 已经有了纪元时间和时区:

// formatter.parse(time) :
{InstantSeconds=1559456477},ISO,Australia/Adelaide resolved to 2019-06-02T15:51:17

我的问题是如何从 formatter.parse(time) 中提取时区(这里是 Australia/Adelaide)，它是 Parsed 类型，以便在中动态使用时区atZone() 在这一行？ :

ZonedDateTime localDateTime = LocalDateTime.from(formatter.parse(time)).
                                     atZone(ZoneId.of("Australia/Adelaide"));

甚至 Furthur，如何从 formatter.parse(time) 响应中提取 InstantSeconds=1559456477 以避免采取以下更多步骤来获取纪元时间戳？ :

ZonedDateTime localDateTime = LocalDateTime.from(formatter.parse(time)).
                                     atZone(ZoneId.of("Australia/Adelaide"));

localDateTime.toInstant().toEpochMilli();

Answer 1

DateTimeFormatter.parse 方法返回 TemporalAccessor其中包含日期、时间和一些其他信息，您可以通过查询获取该信息

default <R> R query(TemporalQuery<R> query)

Framework-level interface defining read-only access to a temporal object, such as a date, time, offset or some combination of these.

This is the base interface type for date, time and offset objects. It is implemented by those classes that can provide information as fields or queries.

TemporalQuery是功能接口(interface)

The most common implementations are method references, such as LocalDate::from and ZoneId::from. Additional common queries are provided as static methods in TemporalQueries.

String time = "2 Jun 2019 03:51:17 PM ACST";
String pattern = "d MMM yyyy hh:mm:ss a z";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);

TemporalAccessor parsedTime = formatter.parse(time);

ZoneId zone = parsedTime.query(ZoneId::from);

LocalDateTime localDateTime = parsedTime.query(LocalDateTime::from);

Instant instant = parsedTime.query(Instant::from);

System.out.println(zone);
System.out.println(localDateTime);
System.out.println(instant);