获取Java中日期范围内的所有星期五
我最近遇到了一个任务，我必须在一个日期范围内获得所有星期五。 我写了一小段代码，惊讶地看到一些奇怪的行为。
以下是我的代码：
public class Friday { public static void main(String[]args){ String start = "01/01/2009"; String end = "12/09/2013"; String[] startTokens = start.split("/"); String[] endTokens = end.split("/"); Calendar startCal = new GregorianCalendar(Integer.parseInt(startTokens[2]),Integer.parseInt(startTokens[1])-1,Integer.parseInt(startTokens[0])); Calendar endCal = new GregorianCalendar(Integer.parseInt(endTokens[2]),Integer.parseInt(endTokens[1])-1, Integer.parseInt(endTokens[0])); int startYear = Integer.parseInt(startTokens[2]); int endYear = Integer.parseInt(endTokens[2]); int startWeek = startCal.get(Calendar.WEEK_OF_YEAR); int endWeek = endCal.get(Calendar.WEEK_OF_YEAR); Calendar cal = new GregorianCalendar(); cal.set(Calendar.DAY_OF_WEEK, Calendar.FRIDAY); // cal.setMinimalDaysInFirstWeek(7); ArrayList main = new ArrayList(); while(startYear <= endYear ){ cal.set(Calendar.YEAR, startYear); System.out.println(cal.getMinimalDaysInFirstWeek()); if(startYear == endYear){ main.addAll(getFridays(startWeek, endWeek, cal)); } else{ main.addAll(getFridays(startWeek, 52, cal)); startWeek = 1; } startYear =startYear +1; } for(String s: main){ System.err.println(s); } } public static ArrayList getFridays(int startWeek, int endWeek, Calendar cal){ ArrayList fridays = new ArrayList(); while(startWeek <= endWeek){ cal.set(Calendar.WEEK_OF_YEAR, startWeek); fridays.add(cal.getTime().toString()); startWeek = startWeek+1; } return fridays; } } 现在当我运行代码时，我发现2011年的星期五不见了。 经过一些调试和在线浏览后，我发现Calendar.WEEK_OF_YEAR是特定于语言环境的，我必须使用setMinimalDaysInFirstWeek(7)来修复它。
所以取消注释上面代码中的相关行。
根据我的理解，现在每年的第一周应从一周的整周开始。
例如2010年1月1日是星期五。 但它不应该出现在结果中，因为我将它配置为对待那一周从1月3日开始。 但是现在我仍然把1月1日视为星期五
我非常困惑。 有人可以解释为什么会这样吗？
这些Stackoverflow文章对我有所帮助：
为什么2010年12月31日作为一年中的一周返回1？
了解java.util.Calendar WEEK_OF_YEAR
这是一个更简单的方法，使用精彩的http://www.joda.org/joda-time/库：
String start = "01/01/2009"; String end = "12/09/2013"; DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy"); DateTime startDate = pattern.parseDateTime(start); DateTime endDate = pattern.parseDateTime(end); List fridays = new ArrayList<>(); while (startDate.isBefore(endDate)){ if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){ fridays.add(startDate); } startDate = startDate.plusDays(1); }
在这结束时，你将在星期五arrays周五。 简单？
或者如果你想加快速度，一旦你周五结束，你可以从使用天数转换为使用周数：
String start = "01/01/2009"; String end = "12/09/2013"; DateTimeFormatter pattern = DateTimeFormat.forPattern("dd/MM/yyyy"); DateTime startDate = pattern.parseDateTime(start); DateTime endDate = pattern.parseDateTime(end); List fridays = new ArrayList<>(); boolean reachedAFriday = false; while (startDate.isBefore(endDate)){ if ( startDate.getDayOfWeek() == DateTimeConstants.FRIDAY ){ fridays.add(startDate); reachedAFriday = true; } if ( reachedAFriday ){ startDate = startDate.plusWeeks(1); } else { startDate = startDate.plusDays(1); } }
首先，我不会打扰周。 将日历设置为范围的开头，并确定它是哪个DOW，然后递增到下一个星期五，然后简单地循环添加7天，直到您在范围的末尾。
实际上，既然你只是前进，应该是这样的：
int daysToAdd = FridayDOW - currentDOW; if (daysToAdd < 0) daysToAdd += 7; Date startDate = currentDate.add(Calendar.DAYS, daysToAdd);
是的，就像那样。
好吧，实际上，对于踢，这里是Java 8：
@Test public void canFindAllFridaysInRange(){ start = LocalDate.of(2013, 5, 10); end = LocalDate.of(2013, 8,30); DayOfWeek dowOfStart = start.getDayOfWeek(); int difference = DayOfWeek.FRIDAY.getValue() - dowOfStart.getValue(); if (difference < 0) difference += 7; List fridaysInRange = new ArrayList (); LocalDate currentFriday = start.plusDays(difference); do { fridaysInRange.add(currentFriday); currentFriday = currentFriday.plusDays(7); } while (currentFriday.isBefore(end)); System.out.println("Fridays in range: " + fridaysInRange); }
一定要喜欢新的日期课！ 当然lambda会进一步浓缩。
TL;博士
someLocalDate.with( // Date-only value without time-of-day and without time zone, represented by `LocalDate` class. TemporalAdjusters.nextOrSame ( DayOfWeek.FRIDAY ) ) // Moving from one `LocalDate` object to another, to find the next Friday unless the starting date is already a Friday. ) // Return a `LocalDate` object.
java.time
其他答案已过时。 旧的java.util.Date/.Calendar类已在Java 8及更高版本的新java.time框架中取代。 Joda-Time库非常出色，继续保持，甚至启发了java.time。 但Joda-Time团队建议尽快转到java.time。
LocalDate
java.time类包括LocalDate ，它是一个仅限日期的值，没有时间或时区。 请参阅教程 。
首先解析输入字符串以获取LocalDate对象。
String inputStart = "01/01/2009"; String inputStop = "12/09/2013"; // 258 Fridays. // String inputStop = "01/01/2009"; // 0 Friday. // String inputStop = "01/02/2009"; // 1 Friday. DateTimeFormatter formatter = DateTimeFormatter.ofPattern ( "MM/dd/yyyy" ); LocalDate start = LocalDate.parse ( inputStart , formatter ); LocalDate stop = LocalDate.parse ( inputStop , formatter );
在您自己的代码中，在输入错误的情况下尝试捕获exception。 并validationstop确实与start相同或晚。
TemporalAdjusters
java.time框架包含TemporalAdjuster接口，作为转换日期时间值的一种方式。 例如， 获取任何特定日期的下一个或同一个星期五 。 在您的开始日期， with(TemporalAdjuster adjuster)调用with(TemporalAdjuster adjuster)从TemporalAdjusters类中传递with(TemporalAdjuster adjuster)的预定义实现（注意复数s ）。 请参阅教程 。
List fridays = new ArrayList<> (); // Collect each Friday found. LocalDate nextOrSameFriday = start.with ( TemporalAdjusters.nextOrSame ( DayOfWeek.FRIDAY ) ); // Loop while we have a friday in hand (non-null) AND that friday is not after our stop date (isBefore or isEqual the stop date). while ( ( null != nextOrSameFriday ) & ( ! nextOrSameFriday.isAfter ( stop ) ) ) { fridays.add ( nextOrSameFriday ); // Remember this friday. nextOrSameFriday = nextOrSameFriday.plusWeeks ( 1 ); // Move to the next Friday, setting up for next iteration of this loop. }
转储到控制台。
System.out.println ( "From: " + start + " to: " + stop + " are " + fridays.size () + " Fridays: " + fridays );
自：2009-01-01至：2013-12-09为258周五：[2009-01-02,2009-01-09,2009-01-16,2009-01-23,2009-01-30,2009 -02-06,2009-02-13,2009-02-20,2009-02-27,2009-03-06,2009-03-13,2009-03-20,2009-03-27,2009-04 -03,2009-04-10,2009-04-17,2009-04-24,2009-05-01,2009-05-08,2009-05-15,2009-05-22,2009-05-29 ，2009-06-05,2009-06-12,2009-06-19,2009-06-26,2009-07-03,2009-07-10,2009-07-17,2009-07-24,2009 -07-31,2009-08-07,2009-08-14,2009-08-21,2009-08-28,2009-09-04,2009-09-11,2009-09-18,2009-09 -25,2009-10-02,2009-10-09,2009-10-16,2009-10-23,2009-10-30,2009-11-06,2009-11-13,2009-11-20 ，2009-11-27,2009-12-04,2009-12-11,2009-12-18,2009-12-25,2010-01-01,2010-01-08,2010-01-15,2010 -01-22,2010-01-29,2010-02-05,2010-02-02,2010-02-19,2010-02-26,2010-03-03,2010-03-03,2010-03-03 -19,2010-03-26,2010-04-02,2010-04-09,2010-04-16,2010-04-23,2010-04-04,2010-05-07,2010-05-14 ，2010-05-21,2010-05-28,2010-06-06,2010-06-06,2010-06-18,2010-06-06,2010-07-02,20 10-07-09,2010-07-16,2010-07-23,2010-07-30,2010-08-08,2010-08-08,2010-08-08,2010-08-08,2010- 09-03,2010-09-10,2010-09-17,2010-09-24,2010-10-01,2010-10-10,2010-10-10,2010-10-10,2010-10-10- 29,2010-11-05,2010-11-12,2010-11-19,2010-11-26,2010-12-03,2010-12-12,2010-12-12,2010-12-24， 2010-12-31,2011-01-07,2011-01-14,2011-01-21,2011-01-28,2011-02-04,2011-02-11,2011-02-18,2011- 02-25,2011-03-04,2011-03-11,2011-03-18,2011-03-25,2011-04-01,2011-04-08,2011-04-15,2011-04- 22,2011-04-29,2011-05-06,2011-05-13,2011-05-20,2011-05-27,2011-06-03,2011-06-10,2011-06-17， 2011-06-24,2011-07-01,2011-07-08,2011-07-15,2011-07-22,2011-07-29,2011-08-05,2011-08-12,2011- 08-19,2011-08-26,2011-09-02,2011-09-09,2011-09-16,2011-09-23,2011-09-30,2011-10-07,2011-10- 14,2011-10-21,2011-10-28,2011-11-04,2011-11-11,2011-11-18,2011-11-25,2011-12-02,2011-12-09， 2011-12-16,2011-12-23,2011-12-30,2012-01-06,2012-01-13,2012-01-20,2012-01-27,2012-02-03,2012- 0 2-10,2012-02-17,2012-02-24,2012-03-02,2012-03-09,2012-03-16,2012-03-23,2012-03-30,2012-04- 06,2012-04-13,2012-04-20,2012-04-27,2012-05-04,2012-05-11,2012-05-18,2012-05-25,2012-06-01， 2012-06-08,2012-06-15,2012-06-22,2012-06-29,2012-07-06,2012-07-13,2012-07-20,2012-07-27,2012- 08-03,2012-08-10,2012-08-17,2012-08-24,2012-08-31,2012-09-07,2012-09-14,2012-09-21,2012-09- 28,2012-10-05,2012-10-12,2012-10-19,2012-10-26,2012-11-02,2012-11-09,2012-11-16,2012-11-23, 2012-11-30,2012-12-07,2012-12-14,2012-12-21,2012-12-28,2013-01-04,2013-01-11,2013-01-18,2013- 01-25,2013-02-01,2013-02-08,2013-02-15,2013-02-22,2013-03-01,2013-03-08,2013-03-15,2013-03- 22,2013-03-29,2013-04-05,2013-04-12,2013-04-19,2013-04-26,2013-05-03,2013-05-10,2013-05-17， 2013-05-24,2013-05-31,2013-06-07,2013-06-06,2013-06-21,2013-06-28,2013-07-05,2013-07-12,2013- 07-19,2013-07-26,2013-08-02,2013-08-08,2013-08-16,2013-08-23,2013-08-30,2013-09-06,2013-09- 13 ，2013-09-20,2013-09-27,2013-10-04,2013-10-11,2013-10-18,2013-10-25,2013-11-01,2013-11-08,2013 -11-15,2013-11-22,2013-11-29,2013-12-06]
关于java.time
java.time框架内置于Java 8及更高版本中。 这些类取代了麻烦的旧遗留日期时间类，如java.util.Date ， Calendar和SimpleDateFormat 。
现在处于维护模式的Joda-Time项目建议迁移到java.time类。
要了解更多信息，请参阅Oracle教程 。 并搜索Stack Overflow以获取许多示例和解释。 规范是JSR 310 。
使用符合JDBC 4.2或更高版本的JDBC驱动程序 ，您可以直接与数据库交换java.time对象。 不需要字符串也不需要java.sql。*类。
从哪里获取java.time类？
- Java SE 8 ， Java SE 9及更高版本
- 内置。
- 带有捆绑实现的标准Java API的一部分。
- Java 9增加了一些小function和修复。
- Java SE 6和Java SE 7
- 许多java.timefunction都被反向移植到ThreeTen-Backport中的 Java 6和7。
- Android的
- 更高版本的Android捆绑java.time类的实现。
- 对于早期的Android， ThreeTenABP项目采用ThreeTen-Backport （如上所述）。 请参见如何使用ThreeTenABP ….
ThreeTen-Extra项目使用其他类扩展了java.time。 该项目是未来可能添加到java.time的试验场。 您可以在这里找到一些有用的课程，如Interval ， YearWeek ， YearQuarter等。
此代码将打印星期五的所有日期。
public class Friday { public static void main(String[] args) throws ParseException { String start = "01/01/2013"; String end = "12/01/2013"; SimpleDateFormat dateFormat=new SimpleDateFormat("dd/MM/yyyy"); Calendar scal=Calendar.getInstance(); scal.setTime(dateFormat.parse(start)); Calendar ecal=Calendar.getInstance(); ecal.setTime(dateFormat.parse(end)); ArrayList fridayDates=new ArrayList<>(); while(!scal.equals(ecal)){ scal.add(Calendar.DATE, 1); if(scal.get(Calendar.DAY_OF_WEEK)==Calendar.FRIDAY){ fridayDates.add(scal.getTime()); } } System.out.println(fridayDates); } }
这里有一个基于Java-8的新流特性并使用我的库Time4J （v4.18或更高版本）的解决方案：
String start = "01/01/2009"; String end = "12/09/2013"; ChronoFormatter f = ChronoFormatter.ofDatePattern("dd/MM/yyyy", PatternType.CLDR, Locale.ROOT); PlainDate startDate = f.parse(start).with(PlainDate.DAY_OF_WEEK.setToNextOrSame(Weekday.FRIDAY)); PlainDate endDate = f.parse(end); Stream fridays = DateInterval.stream(Duration.of(1, CalendarUnit.WEEKS), startDate, endDate); fridays.forEachOrdered(System.out::println); // output 2009-01-02 2009-01-09 ... 2013-08-30 2013-09-06 // other example: list of fridays in ISO-8601-format List result = DateInterval.between(startDate, endDate) .stream(Duration.of(1, CalendarUnit.WEEKS)) .map((date) -> date.toString()) // or maybe use dd/MM/yyyy => f.format(date) .collect(Collectors.toList());
顺便说一下，Java-9将提供类似的解决方案（但具有独占的结束日期边界），另请参阅此增强问题 。
与Lamma日期 ：
List fridays = Dates.from(2015, 12, 1).to(2016, 1, 1).byWeek().on(DayOfWeek.FRIDAY).build(); for (Date friday: fridays) { System.out.println(friday); }
public static List getWeekNumberList(Date currentMonthDate) { List dates = new ArrayList<>(10); Calendar startCalendar = Calendar.getInstance(); startCalendar.setTime(currentMonthDate); startCalendar.set(Calendar.DAY_OF_MONTH, startCalendar.getActualMinimum(Calendar.DAY_OF_MONTH)); Calendar endCalendar = Calendar.getInstance(); endCalendar.setTime(currentMonthDate); endCalendar.set(Calendar.DAY_OF_MONTH, endCalendar.getActualMaximum(Calendar.DAY_OF_MONTH)); Date enddate = endCalendar.getTime(); while (startCalendar.getTime().before(enddate)) { if (startCalendar.get(Calendar.DAY_OF_WEEK) == Calendar.MONDAY) { Date result = startCalendar.getTime(); dates.add(result); startCalendar.add(Calendar.WEEK_OF_MONTH, 1); } else { startCalendar.add(Calendar.DAY_OF_MONTH, 1); } } return dates; }