使用 java 8 DateTime API 解析日期和 AM/PM

java java-8 java-time

2022-09-04 21:06:35

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。我使用以下模式：我希望解析的 LocalDateTime 时间部分设置为 AM/PM 标记或取决于 AM/PM 标记。17/02/2015 PMdd/MM/yyyy aa12:00:0000:00:00

使用以前的 API，使用此模式解析按预期工作。java.text.SimpleDateFormat

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"));

我得到了以下异常：

Exception in thread "main" java.lang.IllegalArgumentException: Too many pattern letters: a
at 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)

如果我将模式切换到，那么我得到了folowing异常：dd/MM/yyyy a

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，当我做反向操作，格式化时，它工作正常：

 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")));

分别打印和 .17/02/2015 AM17/02/2015 PM

用于说的 javadoc （§Resolving， step #6）：java.time.DateTimeFormatter

如果一天中至少有一小时可用，则形成 LocalTime。这涉及提供分钟、秒和秒的小数部分的默认值。

我所理解的是，字段小时一天是解析LocalDateTime所必需的...难道没有办法仅使用AM / PM字段来解析时间部分吗？

答案 1

您可以通过 DateTimeFormatterBuilder.parseDefaulting 设置不可用字段的默认值：

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

答案 2