java - Java:如何获得匹配模式的下一次
问题描述
是否有一种简单/直接的方法可以使用 DateTimeFormatter 模式来获取与该模式匹配的下一个 LocalDateTime 时间?
我想用它来轻松获取下一次事件应该发生的时间(可以是每天、每周、每月等)。例如,如果事件发生在“星期一 12:00 AM”,我想获得下星期一 12:00 AM 的 LocalDateTime。
/**Get next LocalDateTime that matches this input
*
* @param input a String for time matching the pattern: [dayOfWeek ][dayOfMonth ][month ][year ]<timeOfDay> <AM/PM>
* @return LocalDateTime representing the next time that matches the input*/
public LocalDateTime getNextTime(String input) {
LocalDateTime currentTime = LocalDateTime.now();
DateTimeFormatter format = DateTimeFormatter.ofPattern("[eeee ][d ][MMMM ][u ]h:m a");
TemporalAccessor accessor = format.parse(input);
// TODO somehow get the next time (that's after currentTime) that matches this pattern
// LocalDateTime time = ???
return time;
}
我不能这样做LocalDateTime.from(accessor)
,因为输入中可能没有指定年份、月份或月份中的某天。
为了澄清,这里有一些我想要的例子:
// if current date is Friday, January 1st, 2021 at 12:00 PM
// this should return a LocalDateTime for Monday, January 4th, 2021 12:00 AM
getNextTime("Monday 12:00 AM");
// should return Saturday, January 2nd, 2021 12:00 AM
getNextTime("12:00 AM");
// should return Tuesday, January 5th, 2021 12:00 AM
getNextTime("5 January 12:00 AM");
// should return Friday, January 8th, 2021 12:00 PM (must be AFTER current time)
getNextTime("Friday 12:00 PM");
解决方案
不,没有一种简单或直接的方法可以满足您的要求。它涉及相当多的编码。您基本上有 16 个案例,因为每年、每月、每月的某一天和每周的某一天都可能出现,也可能不出现。而且您或多或少将不得不分别处理每个案例。
也可能不会有下一次了。如果年份是 2019 年,则没有。如果字符串是Friday 12 January 2021 2:00 AM
,则不是因为 1 月 12 日是星期二,而不是星期五。
private static DateTimeFormatter format = DateTimeFormatter
.ofPattern("[eeee ][uuuu ][d ][MMMM ][uuuu ]h:m a", Locale.ENGLISH);
// input = [dayOfWeek] [dayOfMonth] [month] [year] <timeOfDay> <AM/PM>
public static LocalDateTime next(String text) {
TemporalAccessor accessor;
try {
accessor = format.parse(text);
} catch (DateTimeParseException dtpe) {
return null;
}
LocalDateTime now = LocalDateTime.now(ZoneId.systemDefault());
LocalTime parsedTime = LocalTime.from(accessor);
LocalDate earliest = now.toLocalDate();
if (parsedTime.isBefore(now.toLocalTime())) {
earliest = earliest.plusDays(1);
}
return resolveYearMonthDomDow(earliest, accessor).atTime(parsedTime);
}
private static LocalDate resolveYearMonthDomDow(LocalDate earliest, TemporalAccessor accessor) {
if (accessor.isSupported(ChronoField.YEAR)) {
Year parsedYear = Year.from(accessor);
if (parsedYear.isBefore(Year.from(earliest))) {
return null;
}
return resolveMonthDomDow(parsedYear, earliest, accessor);
} else {
Year candidateYear = Year.from(earliest);
while (true) {
LocalDate resolved = resolveMonthDomDow(candidateYear, earliest, accessor);
if (resolved != null) {
return resolved;
}
candidateYear = candidateYear.plusYears(1);
}
}
}
private static LocalDate resolveMonthDomDow(Year year, LocalDate earliest, TemporalAccessor accessor) {
if (accessor.isSupported(ChronoField.MONTH_OF_YEAR)) {
YearMonth knownYm = year.atMonth(accessor.get(ChronoField.MONTH_OF_YEAR));
if (knownYm.isBefore(YearMonth.from(earliest))) {
return null;
}
return resolveDomDow(knownYm, earliest, accessor);
} else {
YearMonth candidateYearMonth = YearMonth.from(earliest);
if (candidateYearMonth.getYear() < year.getValue()) {
candidateYearMonth = year.atMonth(Month.JANUARY);
}
while (candidateYearMonth.getYear() == year.getValue()) {
LocalDate resolved = resolveDomDow(candidateYearMonth, earliest, accessor);
if (resolved != null) {
return resolved;
}
candidateYearMonth = candidateYearMonth.plusMonths(1);
}
return null;
}
}
private static LocalDate resolveDomDow(YearMonth ym, LocalDate earliest, TemporalAccessor accessor) {
if (accessor.isSupported(ChronoField.DAY_OF_MONTH)) {
int dayOfMonth = accessor.get(ChronoField.DAY_OF_MONTH);
if (dayOfMonth > ym.lengthOfMonth()) {
return null;
}
LocalDate resolved = ym.atDay(dayOfMonth);
if (resolved.isBefore(earliest)) {
return null;
} else {
return resolveDow(resolved, accessor);
}
} else {
LocalDate candidateDate = earliest;
if (YearMonth.from(earliest).isBefore(ym)) {
candidateDate = ym.atDay(1);
}
while (YearMonth.from(candidateDate).equals(ym)) {
LocalDate resolved = resolveDow(candidateDate, accessor);
if (resolved != null) {
return resolved;
}
candidateDate = candidateDate.plusDays(1);
}
return null;
}
}
private static LocalDate resolveDow(LocalDate date, TemporalAccessor accessor) {
if (accessor.isSupported(ChronoField.DAY_OF_WEEK)) {
if (date.getDayOfWeek().getValue() == accessor.get(ChronoField.DAY_OF_WEEK)) {
return date;
} else {
return null;
}
} else {
return date;
}
}
让我们试一试:
String input = "Monday 12:00 AM";
// get the next time that matches this pattern
LocalDateTime time = next(input);
System.out.println(time);
刚才跑的时候输出(2021年1月11日星期一晚上):
2021-01-18T00:00
所以下周一。看起来不错。
举一个不同的例子,表明闰年得到尊重:
String input = "Wednesday 29 February 12:00 AM";
2040-02-29T00:00
我的代码中很可能存在错误,但基本思想是有效的。
一天中的时间没有问题。挑战在于日期。我正在使用一天中的时间来确定今天的日期是否是最早的候选人。如果现在的时间已经超过了字符串中的时间,那么最早的可能日期就是明天。对于您的示例字符串,Monday 12:00 AM
实际上总是如此:它总是在午夜 12 点之后。
Monday 25 12:00 AM
由于 25 可能是一年(几千年前)或一个月中的一天,因此您一直模棱两可。我通过坚持四位数的年份解决了这个问题。因此,如果一个数字在一周中某一天的开头或之后有四位数字,则为一年,否则为一个月中的某一天。我使用的格式化程序看起来很有趣,一年来了两次。我需要这个来强制解析在尝试每月的某天之前尝试一年,否则有时需要一个四位数的数字作为月份的某天。这反过来意味着格式化程序接受的格式太多了。我认为这在实践中不会成为问题。
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