Java下个月的最后日期

Question

How to get the last date of next month in Java?

Background: I have project, user only interested in the orders should be completed by the end of next month. So I need to get the last date of next month and compare to the order end date, if the order end date smaller than the last date of next month, that means this order should be selected out.

My solution is like this, but not sure is it the best one:

public static boolean shouldCompleteByNextMonth(final Date endDate) {
    final LocalDate now = LocalDate.now(); // Get current local date. 
    final LocalDate nextMonth = now.plusMonths(1); // Get next month.
    final int daysInNextMonth = nextMonth.lengthOfMonth(); // Get the length of next month
    final LocalDate lastLocalDateOfNextMonth = nextMonth.plusDays(daysInNextMonth - now.getDayOfMonth());  // Get the last Date of next month

    // default time zone
    final ZoneId defaultZoneId = ZoneId.systemDefault();

    // convert last locale date to a Date
    final Date lastDateOfNextMonth = Date.from(lastLocalDateOfNextMonth.atStartOfDay(defaultZoneId).toInstant());

    // Compare with the given endDate, if last date of next month is after it, return true, else, return false.
    return lastDateOfNextMonth.after(endDate);
}

Answer 1

The TemporalAdjusters class contains some static TemporalAdjuster s, amongst them lastDayOfMonth() , so you can do

LocalDate.now()
         .plusMonth(1)
         .with(TemporalAdjusters.lastDayOfMonth());

Answer 2

It seems easier to calculate the first day of the month after that and then substracting one day...

LocalDate targetDate = LocalDate.now()
                                .withDayOfMonth(1)
                                .plusMonths(2)
                                .minusDays(1);

Answer 3

tl;dr

YearMonth
.now( 
    ZoneId.of( "Africa/Tunis" )
)
.plusMonths( 1 ) 
.atEndOfMonth()

Returns a LocalDate .

.toString() : 2019-12-31

But… better to use Half-Open approach rather than last day of month.

YearMonth

The YearMonth class represents a month as a whole.

ZoneId z = ZoneId.of( "America/Montreal" ) ;
YearMonth nextMonth = YearMonth.now( z ).plusMonths( 1 ) ;

Notice the use of time zone, ZoneId . For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight on November 30th in Tokyo Japan is a new month, while in Toledo Ohio US it is still “last month”. So if at runtime the current moment is on the first or last day of the month, the time zone is required for accuracy in determining the current month.

Ask for a LocalDate for the last day of month.

LocalDate lastDayOfMonth = nextMonth.atEndOfMonth() ; 

Half-Open

The approach commonly taken in defying a span of time is the Half-Open approach. The beginning is inclusive while the ending is exclusive .

This means a day begins with the first moment of the day (usually 00:00, but not always), and runs up to, but does not include, the first moment of the next day.

In your case, a month begi s on the first and runs up to, but does include, the first of the next month.

The Half-Open approach allows for spans of time that nearly abut one another without gaps.

Your search criteria logic should be find orders where the order is equal to or greater than the first of the month AND less than the first of the following month. In Java that would be >= && < .

A simpler form of that logic is find orders where the order date is not before the first of month AND *is before** the first of following month.

ZoneId z = ZoneId.of( "America/Montreal" ) ;
YearMonth nextMonth = YearMonth.now( z ).plusMonths( 1 ) ;
LocalDate start = nextMonth.atDay( 1 ) ;
LocalDate stop = nextMonth.plusMonths( 1 ).atDay( 1 ) ;

LocalDateRange

Add the ThreeTen-Extra library to your project to benefit from LocalDateRange . This class represents a span of time as a pair of LocalDate objects. It offers handy methods for comparisons such as abuts and contains .

LocalDateRange nextMonthRange = 
    LocalDateRange.of(
        nextMonth.atDay( 1 ) ,
        nextMonth.plusMonths( 1 ).atDay( 1 )
    ) 
;

Database

You mention a database in your Question.

Here is a rough-draft of example JDBC code for querying for orders through the next month. That is, orders whose due-date is before the first day of the month after next month.

Notice how we add two months to the current month, to get the month after next.

The key part of the SQL is: WHERE due_date_ < ? for a Half-Open query of dates running up to, but not including, the passed date (the first of month after next month).

ZoneId z = ZoneId.of( "Pacific/Auckland" ) ;
LocalDate firstOfMonthAfterNextMonth = YearMonth.now( z ).plusMonths( 2 ).atDay( 1 ) ;

String sql = "SELECT order_number_ FROM order_ WHERE due_date_ < ? ; " ;
try(
    Connection conn = myDataSource.getConnection() ;
    PreparedStatement ps = conn.prepareStatement( sql ) ;
)
{
    ps.setObject( 1 ; firstOfMonthAfterNextMonth ) ;
    try(
        ResultSet rs = ps.executeQuery() ;
    )
    {
        while ( rs.next() ) {
            …
        }
    }
} catch ( SQLException e ) {
    e.printStackTrace();
    … 
} catch ( SQLTimeoutException  e ) {
    e.printStackTrace();
    …
}