使用Java 8 DateTime API解析日期和AM / PM
我正在尝试使用Java 8 DateTime API解析日期时间字符串。
要解析的字符串包含日期,月份,年份和AM / PM标记,例如17/02/2015 PM
。我使用以下模式:dd/MM/yyyy
aa并且我希望将解析的LocalDateTime时间部分设置为AM / PM标记12:00:00
或00:00:00
取决于AM / PM标记。
使用以前的java.text.SimpleDateFormat
API,解析可以使用此模式按预期进行。
但是当我使用Java 8 DateTime API并运行以下代码时:
LocalDateTime.parse("17/02/2015 PM", DateTimeFormatter.ofPattern("dd/MM/yyyy aa"));
我得到以下异常:
Exception in thread "main" java.lang.IllegalArgumentException: Too many pattern letters: aat java.time.format.DateTimeFormatterBuilder.parseField(DateTimeFormatterBuilder.java:1765)
at java.time.format.DateTimeFormatterBuilder.parsePattern(DateTimeFormatterBuilder.java:1604)
at java.time.format.DateTimeFormatterBuilder.appendPattern(DateTimeFormatterBuilder.java:1572)
at java.time.format.DateTimeFormatter.ofPattern(DateTimeFormatter.java:534)
如果我将模式切换为,dd/MM/yyyy a
则出现以下异常:
Exception in thread "main" java.time.format.DateTimeParseException: Text '17/02/2015 PM' could not be parsed: Unable to obtain LocalDateTime from TemporalAccessor: {AmPmOfDay=1},ISO resolved to 2015-02-17 of type java.time.format.Parsed at java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:1918)
at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1853)
at java.time.LocalDateTime.parse(LocalDateTime.java:492)
Caused by: java.time.DateTimeException: Unable to obtain LocalDateTime from TemporalAccessor: {AmPmOfDay=1},ISO resolved to 2015-02-17 of type java.time.format.Parsed
at java.time.LocalDateTime.from(LocalDateTime.java:461)
at java.time.LocalDateTime$$Lambda$7/474675244.queryFrom(Unknown Source)
at java.time.format.Parsed.query(Parsed.java:226)
at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1849)
... 2 more
Caused by: java.time.DateTimeException: Unable to obtain LocalTime from TemporalAccessor: {AmPmOfDay=1},ISO resolved to 2015-02-17 of type java.time.format.Parsed
at java.time.LocalTime.from(LocalTime.java:409)
at java.time.LocalDateTime.from(LocalDateTime.java:457)
... 5 more
同样奇怪的是,当我执行反向操作format时,它运行良好:
System.out.println(LocalDateTime.of(2015, 02, 17, 0, 0, 0).format(DateTimeFormatter.ofPattern("dd/MM/yyyy a"))); System.out.println(LocalDateTime.of(2015, 02, 17, 12, 0, 0).format(DateTimeFormatter.ofPattern("dd/MM/yyyy a")));
分别打印17/02/2015 AM
和17/02/2015 PM
。
的javadoc java.time.DateTimeFormatter
说(§Resolving,步骤#6):
- 如果每天至少有一个小时可用,则会形成LocalTime。这涉及提供分钟,秒和秒的默认值。
我了解的是,必须每天使用小时字段来解析LocalDateTime …仅使用AM / PM字段来解析时间部分是没有办法吗?
回答:
您可以通过DateTimeFormatterBuilder.parseDefaulting
以下方式为不可用字段设置默认值:
DateTimeFormatter formatter = new DateTimeFormatterBuilder() .appendPattern("dd/MM/yyyy a")
.parseDefaulting(ChronoField.HOUR_OF_AMPM, 0) // this is required
.parseDefaulting(ChronoField.MINUTE_OF_HOUR, 0) // optional, but you can set other value
.parseDefaulting(ChronoField.SECOND_OF_MINUTE, 0) // optional as well
.toFormatter();
System.out.println(LocalDateTime.parse("17/02/2015 PM", formatter)); // 2015-02-17T12:00
System.out.println(LocalDateTime.parse("17/02/2015 AM", formatter)); // 2015-02-17T00:00
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