Java 8 DateTimeFormatters常量在哪里定义? [英] Where are the Java 8 DateTimeFormatters constants defined?
问题描述
我正在查看 DateTimeFormatter
类,我想知道常量在哪里M
,EEE定义了
和YY
等。更具体地说,在 ChronoField
和 TextStyle
,它应该返回 DateTimeFormatter
字符串片段,例如(ChronoField.MONTH_OF_YEAR,TextStyle.SHORT)
应映射到字符串MMM
I am looking at the DateTimeFormatter
class and I was wondering where are the constants like "M"
, "EEE"
and "YY"
etc are defined. More specifically there should be code like this somewhere given a ChronoField
and TextStyle
, it should return the DateTimeFormatter
string snippet e.g. (ChronoField.MONTH_OF_YEAR, TextStyle.SHORT)
should map to the string "MMM"
推荐答案
经过一些挖掘,我发现这些是在私有静态最终地图
,名为 FIELD_MAP
,它是 DateTimeFormatBuilder 类:
After some source digging, I found out that these are pre-defined in a private static final Map
, called FIELD_MAP
, which is a member of the DateTimeFormatBuilder class:
/** Map of letters to fields. */
private static final Map<Character, TemporalField> FIELD_MAP = new HashMap<>();
static {
// SDF = SimpleDateFormat
FIELD_MAP.put('G', ChronoField.ERA); // SDF, LDML (different to both for 1/2 chars)
FIELD_MAP.put('y', ChronoField.YEAR_OF_ERA); // SDF, LDML
FIELD_MAP.put('u', ChronoField.YEAR); // LDML (different in SDF)
FIELD_MAP.put('Q', IsoFields.QUARTER_OF_YEAR); // LDML (removed quarter from 310)
FIELD_MAP.put('q', IsoFields.QUARTER_OF_YEAR); // LDML (stand-alone)
FIELD_MAP.put('M', ChronoField.MONTH_OF_YEAR); // SDF, LDML
FIELD_MAP.put('L', ChronoField.MONTH_OF_YEAR); // SDF, LDML (stand-alone)
FIELD_MAP.put('D', ChronoField.DAY_OF_YEAR); // SDF, LDML
FIELD_MAP.put('d', ChronoField.DAY_OF_MONTH); // SDF, LDML
FIELD_MAP.put('F', ChronoField.ALIGNED_DAY_OF_WEEK_IN_MONTH); // SDF, LDML
FIELD_MAP.put('E', ChronoField.DAY_OF_WEEK); // SDF, LDML (different to both for 1/2 chars)
FIELD_MAP.put('c', ChronoField.DAY_OF_WEEK); // LDML (stand-alone)
FIELD_MAP.put('e', ChronoField.DAY_OF_WEEK); // LDML (needs localized week number)
FIELD_MAP.put('a', ChronoField.AMPM_OF_DAY); // SDF, LDML
FIELD_MAP.put('H', ChronoField.HOUR_OF_DAY); // SDF, LDML
FIELD_MAP.put('k', ChronoField.CLOCK_HOUR_OF_DAY); // SDF, LDML
FIELD_MAP.put('K', ChronoField.HOUR_OF_AMPM); // SDF, LDML
FIELD_MAP.put('h', ChronoField.CLOCK_HOUR_OF_AMPM); // SDF, LDML
FIELD_MAP.put('m', ChronoField.MINUTE_OF_HOUR); // SDF, LDML
FIELD_MAP.put('s', ChronoField.SECOND_OF_MINUTE); // SDF, LDML
FIELD_MAP.put('S', ChronoField.NANO_OF_SECOND); // LDML (SDF uses milli-of-second number)
FIELD_MAP.put('A', ChronoField.MILLI_OF_DAY); // LDML
FIELD_MAP.put('n', ChronoField.NANO_OF_SECOND); // 310 (proposed for LDML)
FIELD_MAP.put('N', ChronoField.NANO_OF_DAY); // 310 (proposed for LDML)
}
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