Common Java 8 Date and Time APIs: Getting Today’s Date and More

Java 8 introduced the java.time package, which provides a comprehensive set of classes for handling dates and times. The article walks through practical usages of these core classes.

Getting the current date and extracting its parts:

// Get today's date
System.out.println("今天的日期是:" + LocalDate.now());
// Extract year, month, day
System.out.println("获取年月日信息是:" + LocalDate.now().getYear() + "年" + LocalDate.now().getMonthValue() + "月" + LocalDate.now().getDayOfMonth() + "日");

Creating a specific date and comparing dates for equality:

// Create a specific date (2022-10-18)
LocalDate specificLocalDate = LocalDate.of(2022, 10, 18);
System.out.println("创建特定日期是:" + specificLocalDate);
// Equality checks
System.out.println(LocalDate.now().equals(LocalDate.of(2022, 10, 18))); // false
System.out.println(LocalDate.now().equals(LocalDate.now())); // true

Checking periodic dates such as birthdays or annual inspections using MonthDay:

// Is today October 17?
System.out.println(MonthDay.of(LocalDate.now().getMonth(), LocalDate.now().getDayOfMonth()).equals(MonthDay.of(10, 17))); // true
// Is today October 18?
System.out.println(MonthDay.of(LocalDate.now().getMonth(), LocalDate.now().getDayOfMonth()).equals(MonthDay.of(10, 18))); // false

Obtaining the current time and adding offsets:

// Current time
System.out.println("当前时间为:" + LocalTime.now());
// Add 5 hours, 5 minutes, 5 seconds
System.out.println("当前时间为:" + LocalTime.now() + "当前时间往后5个小时为" + LocalTime.now().plusHours(5));
System.out.println("当前时间为:" + LocalTime.now() + "当前时间往后5分钟为" + LocalTime.now().plusMinutes(5));
System.out.println("当前时间为:" + LocalTime.now() + "当前时间往后5秒钟为" + LocalTime.now().plusSeconds(5));

Calculating future dates with ChronoUnit:

// One week later
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一周后为:" + LocalDate.now().plus(1, ChronoUnit.WEEKS));
// One day later
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一天后为:" + LocalDate.now().plus(1, ChronoUnit.DAYS));
// One month later
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一月后为:" + LocalDate.now().plus(1, ChronoUnit.MONTHS));
// One year later
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一年后为:" + LocalDate.now().plus(1, ChronoUnit.YEARS));

Calculating past dates using minus with the same units:

// One week ago
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一周前为:" + LocalDate.now().minus(1, ChronoUnit.WEEKS));
// One day ago
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一天前为:" + LocalDate.now().minus(1, ChronoUnit.DAYS));
// One month ago
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一月前为:" + LocalDate.now().minus(1, ChronoUnit.MONTHS));
// One year ago
System.out.println("当前日期为:" + LocalDate.now() + "当前日期一年前为:" + LocalDate.now().minus(1, ChronoUnit.YEARS));

Retrieving timestamps in milliseconds:

// UTC timestamp
System.out.println("systemUTC当前时间戳为:" + Clock.systemUTC().millis());
// Default zone timestamp
System.out.println("systemDefaultZone当前时间戳为:" + Clock.systemDefaultZone().millis());
// Instant timestamp
System.out.println("当前时间戳为:" + Instant.now().toEpochMilli());

Comparing dates with isBefore and isAfter:

System.out.println("当前日期:" + LocalDate.now() + "是否早于2022-10-18:" + LocalDate.now().isBefore(LocalDate.of(2022, 10, 18)));
System.out.println("当前日期:" + LocalDate.now() + "是否晚于2022-10-18:" + LocalDate.now().isAfter(LocalDate.of(2022, 10, 18)));

Leap‑year check :

System.out.println("今年是否为闰年:" + LocalDate.now().isLeapYear());

Calculating differences :

// Separate year/month/day difference using Period
Period between = Period.between(LocalDate.now(), LocalDate.of(2033, 12, 30));
System.out.println("当前距离2033-12-30相差" + between.getYears() + "年" + between.getMonths() + "月" + between.getDays() + "日");
// Total difference in various units using until
System.out.println("当前距离2033-12-30总共相差天数:" + LocalDate.now().until(LocalDate.of(2033, 12, 30), ChronoUnit.DAYS));
System.out.println("当前距离2033-12-30总共相差周数:" + LocalDate.now().until(LocalDate.of(2033, 12, 30), ChronoUnit.WEEKS));
System.out.println("当前距离2033-12-30总共相差月数:" + LocalDate.now().until(LocalDate.of(2033, 12, 30), ChronoUnit.MONTHS));
System.out.println("当前距离2033-12-30总共相差年数:" + LocalDate.now().until(LocalDate.of(2033, 12, 30), ChronoUnit.YEARS));

Formatting and parsing between strings and date/time objects:

// Parse a basic ISO date string
System.out.println("格式化20221017后的日期为:" + LocalDate.parse("20221017", DateTimeFormatter.BASIC_ISO_DATE));
// Convert LocalDateTime to a formatted string
System.out.println("日期转换为字符串为:" + LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss")));
// Parse a formatted string back to a date
System.out.println("字符串转换为日期:" + LocalDate.parse("2022/12/17 19:22:42", DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss")));

Each code fragment prints the result as a comment in the original source, illustrating the exact output one would see when running the examples.