我有以毫秒 [1]表示的几个事件的日期，我想知道哪些事件在当前周和当月内，但我无法弄清楚如何获取运行周的第一天（日/月/年）并将其转换为毫秒，该月的第一天也是如此。
[1]Since January 1, 1970, 00:00:00 GMT
答案 0 :(得分：141)
本周以毫秒为单位：
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day !
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
// get start of this week in milliseconds
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
System.out.println("Start of this week: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
// start of the next week
cal.add(Calendar.WEEK_OF_YEAR, 1);
System.out.println("Start of the next week: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
本月以毫秒为单位：
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0); // ! clear would not reset the hour of day !
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
// get start of the month
cal.set(Calendar.DAY_OF_MONTH, 1);
System.out.println("Start of the month: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
// get start of the next month
cal.add(Calendar.MONTH, 1);
System.out.println("Start of the next month: " + cal.getTime());
System.out.println("... in milliseconds: " + cal.getTimeInMillis());
答案 1 :(得分：23)
可以在java.util.Calendar的帮助下确定一周的第一天，如下所示：
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.setTimeInMillis(timestamp);
while (calendar.get(Calendar.DAY_OF_WEEK) > calendar.getFirstDayOfWeek()) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of week.
}
long firstDayOfWeekTimestamp = calendar.getTimeInMillis();
每月的第一天可以确定如下：
Calendar calendar = Calendar.getInstance();
calendar.clear();
calendar.setTimeInMillis(timestamp);
while (calendar.get(Calendar.DATE) > 1) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of month.
}
long firstDayOfMonthTimestamp = calendar.getTimeInMillis();
非常详细，是的。
Java 7将带有一个大大改进的日期和时间API（JSR-310）。如果你还没有切换，那么你可以使用JodaTime来减少这一点：
DateTime dateTime = new DateTime(timestamp);
long firstDayOfWeekTimestamp = dateTime.withDayOfWeek(1).getMillis();
和
DateTime dateTime = new DateTime(timestamp);
long firstDayOfMonthTimestamp = dateTime.withDayOfMonth(1).getMillis();
答案 2 :(得分：13)
Java 8及更高版本中的java.time框架取代了旧的java.util.Date/.Calendar类。旧的课程被证明是麻烦，混乱和有缺陷的。避免它们。
java.time框架的灵感来自高度成功的Joda-Time库，由JSR 310定义，由ThreeTen-Extra项目扩展，并在Tutorial中进行了解释。
Instant Instant类代表UTC中时间轴上的一个时刻。
java.time框架的分辨率为纳秒，或小数秒的9位数。毫秒只是小数秒的3位数。因为millisecond resolution很常见，所以java.time包含一个方便的工厂方法。
long millisecondsSinceEpoch = 1446959825213L;
Instant instant = Instant.ofEpochMilli ( millisecondsSinceEpoch );
millisecondsSinceEpoch：1446959825213即时：2015-11-08T05：17：05.213Z
ZonedDateTime 要考虑当前周和当月，我们需要应用特定时区。
ZoneId zoneId = ZoneId.of ( "America/Montreal" );
ZonedDateTime zdt = ZonedDateTime.ofInstant ( instant , zoneId );
在zoneId：America / Montreal：2015-11-08T00：17：05.213-05：00 [America / Montreal]
在日期工作中，我们通常使用半开放方法来定义时间跨度。开头是包含，而结尾是独占。我们得到跟随周（或月）的第一个时刻，而不是尝试确定一周（或月）结束的最后一秒。所以一个星期从星期一的第一个时刻开始运行到但不包括 星期一的第一个时刻。
我们是一周的第一天，也是最后一天。 java.time框架包含一个工具，with方法和ChronoField枚举。
默认情况下，java.time使用ISO 8601标准。因此星期一是一周的第一天（1），星期日是最后一天（7）。
ZonedDateTime firstOfWeek = zdt.with ( ChronoField.DAY_OF_WEEK , 1 ); // ISO 8601, Monday is first day of week.
ZonedDateTime firstOfNextWeek = firstOfWeek.plusWeeks ( 1 );
该周运行时间：2015-11-02T00：17：05.213-05：00 [美国/蒙特利尔]至2015-11-09T00：17：05.213-05：00 [美国/蒙特利尔]
糟糕！查看这些值的时间。我们想要一天的第一时刻。由于夏令时（DST）或其他异常，一天中的第一个时刻并不总是00:00:00.000。所以我们应该让java.time代表我们进行调整。要做到这一点，我们必须通过LocalDate课程。
ZonedDateTime firstOfWeek = zdt.with ( ChronoField.DAY_OF_WEEK , 1 ); // ISO 8601, Monday is first day of week.
firstOfWeek = firstOfWeek.toLocalDate ().atStartOfDay ( zoneId );
ZonedDateTime firstOfNextWeek = firstOfWeek.plusWeeks ( 1 );
那一周的时间从：2015-11-02T00：00-05：00 [美国/蒙特利尔]到2015-11-09T00：00-05：00 [美国/蒙特利尔]
同月也一样。
ZonedDateTime firstOfMonth = zdt.with ( ChronoField.DAY_OF_MONTH , 1 );
firstOfMonth = firstOfMonth.toLocalDate ().atStartOfDay ( zoneId );
ZonedDateTime firstOfNextMonth = firstOfMonth.plusMonths ( 1 );
该月的运行时间为：2015-11-01T00：00-04：00 [美国/蒙特利尔]至2015-12-01T00：00-05：00 [美国/蒙特利尔]
YearMonth 查看一对时刻是否在同一个月的另一种方法是检查相同的YearMonth值。
例如，假设thisZdt和thatZdt都是ZonedDateTime个对象：
boolean inSameMonth = YearMonth.from( thisZdt ).equals( YearMonth.from( thatZdt ) ) ;
我强烈建议不要以毫秒为单位进行日期工作。这确实是日期时间类往往在内部工作的方式，但我们有一些原因。处理来自时代的计数是笨拙的，因为人们无法理解这些值，因此调试和记录很困难且容易出错。而且，正如我们已经看到的，可能会有不同的决议;旧的Java类和Joda-Time库使用毫秒，而像Postgres这样的数据库使用微秒，现在java.time使用纳秒。
您会将文字作为位处理，还是让String，StringBuffer和StringBuilder等类处理此类详细信息？
但是，如果你坚持，从ZonedDateTime得到一个Instant，并从那里得到一个毫秒计数从纪元。但请记住此次调用可能意味着数据丢失。您ZonedDateTime / Instant中可能包含的任何微秒或纳秒都将被截断（丢失）。
long millis = firstOfWeek.toInstant().toEpochMilli(); // Possible data loss.
答案 3 :(得分：11)
注意！
while (calendar.get(Calendar.DAY_OF_WEEK) > calendar.getFirstDayOfWeek()) {
calendar.add(Calendar.DATE, -1); // Substract 1 day until first day of week.
}
是个好主意，但有一些问题： 例如，我来自乌克兰，我国的calendar.getFirstDayOfWeek（）是2（星期一）。 今天是1（星期日）。在这种情况下，calendar.add未被调用。
所以，正确的方法是改变＆＃34;＆gt;＆＃34;到＆＃34;！=＆＃34;：
while (calendar.get(Calendar.DAY_OF_WEEK) != calendar.getFirstDayOfWeek()) {...
答案 4 :(得分：2)
要获得该月的第一天，只需获取Date并将当前日期设置为该月的第1天。如果需要，可以清除小时，分钟，秒和毫秒。
private static Date firstDayOfMonth(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.DATE, 1);
return calendar.getTime();
}
一周的第一天是相同的，但使用Calendar.DAY_OF_WEEK代替
private static Date firstDayOfWeek(Date date) {
Calendar calendar = Calendar.getInstance();
calendar.setTime(date);
calendar.set(Calendar.DAY_OF_WEEK, 1);
return calendar.getTime();
}
答案 5 :(得分：2)
我为此创建了一些方法：
public static String catchLastDayOfCurrentWeek(String pattern) {
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
return calendarToString(cal, pattern);
}
public static String catchLastDayOfCurrentWeek(String pattern) {
Calendar cal = Calendar.getInstance();
cal.set(Calendar.HOUR_OF_DAY, 0);
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
cal.add(Calendar.WEEK_OF_YEAR, 1);
cal.add(Calendar.MILLISECOND, -1);
return calendarToString(cal, pattern);
}
public static String catchTheFirstDayOfThemonth(Integer month, pattern padrao) {
Calendar cal = GregorianCalendar.getInstance();
cal.setTime(new Date());
cal.set(Calendar.MONTH, month);
cal.set(Calendar.DAY_OF_MONTH, 1);
return calendarToString(cal, pattern);
}
public static String catchTheLastDayOfThemonth(Integer month, String pattern) {
Calendar cal = GregorianCalendar.getInstance();
cal.setTime(new Date());
cal.set(cal.get(Calendar.YEAR), month, cal.getActualMaximum(Calendar.DAY_OF_MONTH));
return calendarToString(cal, pattern);
}
public static String calendarToString(Calendar calendar, String pattern) {
if (calendar == null) {
return "";
}
SimpleDateFormat format = new SimpleDateFormat(pattern, LocaleUtils.DEFAULT_LOCALE);
return format.format(calendar.getTime());
}
您可以看到更多here。
答案 6 :(得分：2)
您可以使用java.time软件包（自Java8起）开始获取一天/周/月的开始/结束时间。
下面的util类示例：
import org.junit.Test;
import java.time.DayOfWeek;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;
import java.time.format.DateTimeFormatter;
import java.time.temporal.TemporalAdjusters;
import java.util.Date;
public class DateUtil {
private static final ZoneId DEFAULT_ZONE_ID = ZoneId.of("UTC");
public static LocalDateTime startOfDay() {
return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MIN);
}
public static LocalDateTime endOfDay() {
return LocalDateTime.now(DEFAULT_ZONE_ID).with(LocalTime.MAX);
}
public static boolean belongsToCurrentDay(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfDay()) && localDateTime.isBefore(endOfDay());
}
//note that week starts with Monday
public static LocalDateTime startOfWeek() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MIN)
.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY));
}
//note that week ends with Sunday
public static LocalDateTime endOfWeek() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MAX)
.with(TemporalAdjusters.nextOrSame(DayOfWeek.SUNDAY));
}
public static boolean belongsToCurrentWeek(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfWeek()) && localDateTime.isBefore(endOfWeek());
}
public static LocalDateTime startOfMonth() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MIN)
.with(TemporalAdjusters.firstDayOfMonth());
}
public static LocalDateTime endOfMonth() {
return LocalDateTime.now(DEFAULT_ZONE_ID)
.with(LocalTime.MAX)
.with(TemporalAdjusters.lastDayOfMonth());
}
public static boolean belongsToCurrentMonth(final LocalDateTime localDateTime) {
return localDateTime.isAfter(startOfMonth()) && localDateTime.isBefore(endOfMonth());
}
public static long toMills(final LocalDateTime localDateTime) {
return localDateTime.atZone(DEFAULT_ZONE_ID).toInstant().toEpochMilli();
}
public static Date toDate(final LocalDateTime localDateTime) {
return Date.from(localDateTime.atZone(DEFAULT_ZONE_ID).toInstant());
}
public static String toString(final LocalDateTime localDateTime) {
return localDateTime.format(DateTimeFormatter.ISO_DATE_TIME);
}
@Test
public void test() {
//day
final LocalDateTime now = LocalDateTime.now();
System.out.println("Now: " + toString(now) + ", in mills: " + toMills(now));
System.out.println("Start of day: " + toString(startOfDay()));
System.out.println("End of day: " + toString(endOfDay()));
System.out.println("Does '" + toString(now) + "' belong to the current day? > " + belongsToCurrentDay(now));
final LocalDateTime yesterday = now.minusDays(1);
System.out.println("Does '" + toString(yesterday) + "' belong to the current day? > " + belongsToCurrentDay(yesterday));
final LocalDateTime tomorrow = now.plusDays(1);
System.out.println("Does '" + toString(tomorrow) + "' belong to the current day? > " + belongsToCurrentDay(tomorrow));
//week
System.out.println("Start of week: " + toString(startOfWeek()));
System.out.println("End of week: " + toString(endOfWeek()));
System.out.println("Does '" + toString(now) + "' belong to the current week? > " + belongsToCurrentWeek(now));
final LocalDateTime previousWeek = now.minusWeeks(1);
System.out.println("Does '" + toString(previousWeek) + "' belong to the current week? > " + belongsToCurrentWeek(previousWeek));
final LocalDateTime nextWeek = now.plusWeeks(1);
System.out.println("Does '" + toString(nextWeek) + "' belong to the current week? > " + belongsToCurrentWeek(nextWeek));
//month
System.out.println("Start of month: " + toString(startOfMonth()));
System.out.println("End of month: " + toString(endOfMonth()));
System.out.println("Does '" + toString(now) + "' belong to the current month? > " + belongsToCurrentMonth(now));
final LocalDateTime previousMonth = now.minusMonths(1);
System.out.println("Does '" + toString(previousMonth) + "' belong to the current month? > " + belongsToCurrentMonth(previousMonth));
final LocalDateTime nextMonth = now.plusMonths(1);
System.out.println("Does '" + toString(nextMonth) + "' belong to the current month? > " + belongsToCurrentMonth(nextMonth));
}
}
测试输出：
Now: 2020-02-16T22:12:49.957, in mills: 1581891169957
Start of day: 2020-02-16T00:00:00
End of day: 2020-02-16T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current day? > true
Does '2020-02-15T22:12:49.957' belong to the current day? > false
Does '2020-02-17T22:12:49.957' belong to the current day? > false
Start of week: 2020-02-10T00:00:00
End of week: 2020-02-16T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current week? > true
Does '2020-02-09T22:12:49.957' belong to the current week? > false
Does '2020-02-23T22:12:49.957' belong to the current week? > false
Start of month: 2020-02-01T00:00:00
End of month: 2020-02-29T23:59:59.999999999
Does '2020-02-16T22:12:49.957' belong to the current month? > true
Does '2020-01-16T22:12:49.957' belong to the current month? > false
Does '2020-03-16T22:12:49.957' belong to the current month? > false
答案 7 :(得分：1)
在这种情况下：
// get today and clear time of day
Calendar cal = Calendar.getInstance();
cal.clear(Calendar.HOUR_OF_DAY); <---- is the current hour not 0 hour
cal.clear(Calendar.MINUTE);
cal.clear(Calendar.SECOND);
cal.clear(Calendar.MILLISECOND);
因此Calendar.HOUR_OF_DAY返回当前运行小时数8,9,12,15,18。 我认为通过以下方式更好地改变这一行：
c.set(Calendar.HOUR_OF_DAY,0);
答案 8 :(得分：1)
获取下个月的第一个日期： -
SimpleDateFormat df = new SimpleDateFormat("MM-dd-yyyy");
String selectedDate="MM-dd-yyyy like 07-02-2018";
Date dt = df.parse(selectedDate);`enter code here`
calendar = Calendar.getInstance();
calendar.setTime(dt);
calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH) + 1);
String firstDate = df.format(calendar.getTime());
System.out.println("firstDateof next month ==>" + firstDate);
答案 9 :(得分：0)
您应该能够将您的号码转换为Java日历，例如：
Calendar.getInstance().setTimeInMillis(myDate);
从那里开始，比较不应该太难。
答案 10 :(得分：0)
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.Scanner;
/**
This Program will display day for, 1st and last days in a given month and year
@author Manoj Kumar Dunna
Mail Id : manojdunna@gmail.com
*/
public class DayOfWeek {
public static void main(String[] args) {
String strDate = null;
int year = 0, month = 0;
Scanner sc = new Scanner(System.in);
System.out.print("Enter YYYY/MM: ");
strDate = sc.next();
Calendar cal = new GregorianCalendar();
String [] date = strDate.split("/");
year = Integer.parseInt(date[0]);
month = Integer.parseInt(date[1]);
cal.set(year, month-1, 1);
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));
cal.add(Calendar.MONTH, 1);
cal.add(Calendar.DAY_OF_YEAR, -1);
System.out.println(new SimpleDateFormat("EEEE").format(cal.getTime()));
}
}
答案 11 :(得分：0)
Simple Solution:
package com.util.calendarutil;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
public class CalUtil {
public static void main(String args[]){
DateFormat df = new SimpleDateFormat("dd/mm/yyyy");
Date dt = null;
try {
dt = df.parse("23/01/2016");
} catch (ParseException e) {
System.out.println("Error");
}
Calendar cal = Calendar.getInstance();
cal.setTime(dt);
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
Date startDate = cal.getTime();
cal.add(Calendar.DATE, 6);
Date endDate = cal.getTime();
System.out.println("Start Date:"+startDate+"End Date:"+endDate);
}
}
答案 12 :(得分：0)
在 Java
中LocalDateTime firstOfWeek = LocalDateTime.now().with(ChronoField.DAY_OF_WEEK, 1).toLocalDate().atStartOfDay(); // 2020-06-08 00:00 MONDAY
LocalDateTime firstOfMonth = LocalDateTime.now().with(ChronoField.DAY_OF_MONTH , 1).toLocalDate().atStartOfDay(); // 2020-06-01 00:00
// Convert to milliseconds:
firstOfWeek.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
在科特林
val firstOfWeek = LocalDateTime.now().with(ChronoField.DAY_OF_WEEK, 1).toLocalDate().atStartOfDay() // 2020-06-08 00:00 MONDAY
val firstOfMonth = LocalDateTime.now().with(ChronoField.DAY_OF_MONTH , 1).toLocalDate().atStartOfDay() // 2020-06-01 00:00
// Convert to milliseconds:
firstOfWeek.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli()
答案 13 :(得分：-1)
我使用此技巧来获取当前月份的第一天 注意订单是 1周日 星期一2 周三3 ....等等
transform: translateX(-50%);答案 14 :(得分：-4)
public static void main(String[] args) {
System.out.println(getMonthlyEpochList(1498867199L,12,"Monthly"));
}
public static Map<String,String> getMonthlyEpochList(Long currentEpoch, int noOfTerms, String timeMode) {
Map<String,String> map = new LinkedHashMap<String,String>();
int month = 0;
while(noOfTerms != 0) {
Calendar calendar = Calendar.getInstance();
calendar.add(Calendar.MONTH, month);
calendar.set(Calendar.DATE, calendar.getActualMinimum(Calendar.DAY_OF_MONTH));
Date monthFirstDay = calendar.getTime();
calendar.set(Calendar.DATE, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
Date monthLastDay = calendar.getTime();
map.put(getMMYY(monthFirstDay.getTime()), monthFirstDay + ":" +monthLastDay);
month--;
noOfTerms--;
}
return map;
}