The java.time Package

JDK 1.8 added LocalDateTime and ZonedDateTime to the java.time package. These types make date and time handling safer and more convenient than legacy APIs.

Reference: Why Java Date and Calendar Are a Bad Fit

Getting Dates

LocalDate holds year, month, and day. LocalTime holds hour, minute, and second. LocalDateTime combines both.

// today, 2018-12-11
LocalDate nowDate = LocalDate.now();

// 2018-12-11
LocalDate ofDate = LocalDate.of(2018, 12, 11);

// now, 2018-12-11T13:12:11
LocalDateTime nowDateTime = LocalDateTime.now();

// 2018-12-11T15:23:32
LocalDateTime ofDateTime = LocalDateTime.of(2018, 12, 11, 15, 23, 32);

Getting Specific Dates/Times

Get today at midnight, then format

// midnight today
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS");

// 2018-12-12 00:00:00.000
String date = LocalDate.now().atStartOfDay().format(formatter);

Get tomorrow

// 2018-12-11T15:23:32
LocalDateTime ofDateTime = LocalDateTime.of(2018, 12, 11, 15, 23, 32);

// 2018-12-12T15:23:32
LocalDateTime tomorrow = ofDateTime.plusDays(1);

Get the last moment of tomorrow

// 2018-12-12 23:59:59
// actually 23:59:59.999999999
LocalDateTime.now().plusDays(1).with(LocalTime.MAX);

Get noon

// noon today
LocalDateTime.now().with(LocalTime.NOON);

Converting Dates

Convert date values to strings or from legacy types.

Date to LocalDateTime

// java.util.Date to java.time.LocalDateTime
LocalDateTime.ofInstant(new Date().toInstant(), ZoneId.systemDefault());

LocalDate to LocalDateTime

// java.time.LocalDate to java.time.LocalDateTime
// today at 15:23:30
LocalDate.now().atTime(15, 23, 30);

// today at midnight
LocalDate.now().atStartOfDay();

LocalDateTime to String

// java.time.LocalDateTime to java.lang.String
// 2018-12-11 13:53:21.121
LocalDateTime.now()
    .format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS"));

LocalDate to String

// java.time.LocalDate to java.lang.String
// 2018-12-11
LocalDate.now().format(DateTimeFormatter.ISO_DATE);

String to LocalDateTime

// java.lang.String to java.time.LocalDateTime
// 2018-12-11T13:43:21.222
LocalDateTime.parse("2018-12-11 13:43:21.221",
    DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS"));       

String to LocalDate

// java.lang.String to java.time.LocalDate 
// 2018-12-11
LocalDate.parse("2018-12-11");

Working with Weekdays

You can compute the next weekday or the Nth weekday of a month with compact code.

Next Sunday

// based on Dec 11, next Sunday is Dec 16
LocalDateTime.now().with(TemporalAdjusters.next(DayOfWeek.SUNDAY))

Fourth Sunday of December 2018

// based on Dec 2018, the fourth Sunday is the 23rd
LocalDate.of(2018, 12, 11).with(TemporalAdjusters.dayOfWeekInMonth(4, DayOfWeek.SUNDAY));

First Sunday of December 2018

// based on Dec 2018, the first Sunday is the 2nd
LocalDate.of(2018, 12, 11).with(TemporalAdjusters.firstInMonth(DayOfWeek.SUNDAY));

Locale-Specific Names

You can render month and weekday names in different locales.

// Korean output
Month.FEBRUARY.getDisplayName(TextStyle.FULL, Locale.KOREAN);
Month.FEBRUARY.getDisplayName(TextStyle.NARROW, Locale.KOREAN);
Month.FEBRUARY.getDisplayName(TextStyle.SHORT, Locale.KOREAN);

DayOfWeek.SUNDAY.getDisplayName(TextStyle.FULL, Locale.KOREAN);
DayOfWeek.SUNDAY.getDisplayName(TextStyle.SHORT, Locale.KOREAN);
DayOfWeek.SUNDAY.getDisplayName(TextStyle.NARROW, Locale.KOREAN);

// English output
Month.FEBRUARY.getDisplayName(TextStyle.FULL, Locale.ENGLISH);
Month.FEBRUARY.getDisplayName(TextStyle.SHORT, Locale.ENGLISH);
Month.FEBRUARY.getDisplayName(TextStyle.NARROW, Locale.ENGLISH);

DayOfWeek.SUNDAY.getDisplayName(TextStyle.FULL, Locale.ENGLISH);
DayOfWeek.SUNDAY.getDisplayName(TextStyle.SHORT, Locale.ENGLISH);
DayOfWeek.SUNDAY.getDisplayName(TextStyle.NARROW, Locale.ENGLISH);