Master Java Date & Time: From JDK7 Date to JDK8 LocalDate/LocalDateTime

When working with entity classes, timestamps such as creation time are often stored in databases using datetime or date types, but some legacy code still stores them as varchar. In JDK7, developers commonly used the older Date, Calendar, and SimpleDateFormat classes.

The java.util.Date class has long been criticized for its confusing design: it mixes date, time, and milliseconds, uses midnight to separate dates, counts months from zero, and provides unintuitive methods for extracting year, month, and day. Moreover, both Date and SimpleDateFormat are not type‑safe.

Java 8 introduced a new date‑time API that replaces these older classes.

JDK7 vs JDK8 Date Comparison

JDK7 creating a date: Date date0 = new Date(); JDK8 creating a date: LocalDate today = LocalDate.now(); Output examples:

JDK7 output: Wed Apr 13 13:19:06 CST 2022 JDK8 output: 2022-04-13 Because the JDK7 output is less readable, developers often need to format it with SimpleDateFormat. The JDK8 LocalDate prints directly in an ISO format, eliminating that extra step.

Formatting with SimpleDateFormat (JDK7):

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
String str = sdf.format(date0);

Formatting with DateTimeFormatter (JDK8):

LocalDate now = LocalDate.now();
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy/MM/dd");
String jdk8Time = now.format(formatter);
System.out.println("JDK8 formatted time==" + jdk8Time);

Both produce the same readable date, but the JDK8 code is shorter and the formatter is thread‑safe, unlike SimpleDateFormat, which must be created locally for each use.

Common JDK8 Date/Time Operations

String to LocalDate

LocalDate localDate = LocalDate.now();
DateTimeFormatter fmt = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String dateStr = localDate.format(fmt);
System.out.println("LocalDate to String: " + dateStr);

Result: LocalDate to String: 2022/04/14 Date to LocalDateTime

Date date = new Date();
System.out.println("LocalDateTime(): " + date.toInstant()
    .atZone(ZoneId.systemDefault())
    .toLocalDateTime());

Result: LocalDateTime(): 2022-04-14T10:07:52.868 Timestamp to LocalDateTime

long timestamp = System.currentTimeMillis();
Instant instant = Instant.ofEpochMilli(timestamp);
System.out.println("Timestamp to LocalDateTime: " +
    LocalDateTime.ofInstant(instant, ZoneId.systemDefault()));

Result:

Timestamp to LocalDateTime: 2022-04-14T10:09:14.780

Key LocalDate API Methods

getYear()

– returns the year as an

int

getMonth()

– returns the month as a Month enum getMonthValue() – returns the month number (1‑12) getDayOfWeek() – returns the day of week as

DayOfWeek

getDayOfMonth()

– returns the day of month as an

int

getDayOfYear()

– returns the day of year as an

int

withYear(int year)

– returns a copy with the specified year withMonth(int month) – returns a copy with the specified month withDayOfMonth(int day) – returns a copy with the specified day of month isLeapYear() – checks if the year is a leap year lengthOfMonth() – number of days in the month lengthOfYear() – 365 or 366 days plusYears(long years), plusMonths(long months), plusWeeks(long weeks), plusDays(long days) – add time minusYears(long years), minusMonths(long months), minusWeeks(long weeks), minusDays(long days) – subtract time compareTo(ChronoLocalDate other) – compare two dates isBefore(ChronoLocalDate other) – true if this date is before the other isAfter(ChronoLocalDate other) – true if this date is after the other isEqual(ChronoLocalDate other) – true if dates are equal

These APIs cover most daily development needs for handling dates in Java.