The java.time package of Java 8 provides thread-safe and clear design date and time processing methods. Get the current date and time to use LocalDateTime.now() or ZonedDateTime.now(ZoneId.of("Asia/Shanghai")); 1. Use DateTimeFormatter for formatting, such as ISO_DATE or custom format; 2. The parsing needs to ensure that the string matches the format strictly; 3. Addition and subtraction operations are implemented through plusXxx()/minusXxx(); 4. Use isBefore()/isAfter() for comparison; 5. Use withZoneSameInstant for time zone conversion and support listing of all time zones ZoneId.getAvailableZoneIds().

Java 8 introduces a brand new date and time API ( java.time package), which solves the problems of thread insecure and design chaos in the old version of Date and Calendar classes. This new API is more intuitive, easy to use, and more in line with modern development needs. If you are using Java 8 or later, it is recommended to use classes in java.time to handle dates and times first.

How to get the current date and time?

The most commonly used method is to use LocalDateTime.now() to obtain the time of the current system. It contains information about year, month, day, hour, minute, and seconds, but does not have a time zone.

 LocalDateTime now = LocalDateTime.now();
System.out.println(now); // The output is similar to 2025-04-05T14:30:45.123

If you need to include time zone information, you can use ZonedDateTime.now() :

 ZonedDateTime nowWithZone = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));

Tips: In distributed or internationalized scenarios, it is recommended to always bring time zone information to avoid data deviation due to the server's local time zone settings.

How to format and parse dates?

Use DateTimeFormatter to facilitate formatting of output dates, or parse strings into date objects.

For example, format LocalDate as yyyy-MM-dd :

 LocalDate date = LocalDate.now();
String formatted = date.format(DateTimeFormatter.ISO_DATE);
// Or custom format DateTimeFormatter customFormatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
String custom = date.format(customFormatter); // The output is similar to 2025/04/05

Conversely, if you want to parse from a string to a date:

 String input = "2025-04-05";
LocalDate parsed = LocalDate.parse(input, DateTimeFormatter.ISO_DATE);

Note: The format template must strictly match the input string, otherwise an exception will be thrown. For example, if "2025/04/05" is parsed with ISO_DATE , it will fail.

How to add, subtract and compare dates?

Classes such as LocalDate , LocalDateTime , etc. all provide plusXxx() and minusXxx() methods for addition and subtraction operations.

For example, add three days to the current date:

 LocalDate today = LocalDate.now();
LocalDate threeDaysLater = today.plusDays(3);

You can also add hours, minutes, months, etc.:

• plusHours(1)
• plusMonths(2)
• minusWeeks(1)

The date comparison is also very simple, you can use isBefore() and isAfter() directly:

 LocalDate d1 = LocalDate.of(2025, 4, 5);
LocalDate d2 = LocalDate.of(2025, 4, 6);

boolean isBefore = d1.isBefore(d2); // true

What to do if you encounter a time zone?

When dealing with time conversion across time zones, you can use ZonedDateTime and ZoneId .

For example, converting Beijing time to New York time:

 ZonedDateTime beijingTime = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));
ZonedDateTime newYorkTime = beijingTime.withZoneSameInstant(ZoneId.of("America/New_York"));

This method will automatically consider factors such as daylight saving time, which is more reliable than manually calculating the offset.

If you want to list all available time zone names, you can do this:

 Set<String> zones = ZoneId.getAvailableZoneIds(); // Get all supported time zone names

Basically these common operations. Mastering these points should be enough for processing time in daily development. Although you may be a little uncomfortable at the beginning, after using it a few times, you will find that the design of java.time is really clear and reasonable.

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