1. 代码示例
package time;
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.Calendar;
import java.util.Date;
/***
* 总结: java.util.Date和 SimpleDateFormat 都是非线程安全的
* 1. LocalDate
* 2. LocalTime
* 3. LocalDateTime
* 4. DateTimeFormatter
* 5. ChronoUnit
*/
public class Java8Date {
public static void main(String[] args) {
/** #0. Calendar
* 区别于calendar的month: canlendar中:[]
* 1. LocalDate的年月日直接是日期中的值;
* 2. date.getMonthValue() 和 c.get(Calendar.MONTH) 有区别: c:0表示1月
*/
Calendar c = Calendar.getInstance(); // 测试日期:2019-04-02
System.out.println(c.get(Calendar.YEAR)); // 2019
System.out.println(c.get(Calendar.MONTH)); // 3(0=1月)
System.out.println(c.get(Calendar.DAY_OF_MONTH)); //2
// #1. LocalDate 2019-04-02 : 今日日期: LocalDate.now()
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
LocalDate date = LocalDate.now();
System.out.println(date); // 2019-04-02
// #2. year month day: 年月日获取
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
int year = date.getYear(); // 2019
int month = date.getMonthValue();// 4
int day = date.getDayOfMonth(); // 2
System.out.println(year + "-" + month + "-" + day); // 2019-4-2
// #3. 构造日期: 给定年月日
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
LocalDate dt1 = LocalDate.of(2019, 3, 8);
LocalDate dt2 = LocalDate.of(2019, 3, 8);
// #4. 日期比较: equals
// true: 内部是比较的 year-year month-month day-day
System.out.println(dt2.equals(dt1));
// #5. 周期性日期, 比如: 判断用户的生日
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
// 生日:0308
MonthDay uBirth = MonthDay.of(3, 8);
MonthDay dtMD = MonthDay.from(dt1);
// dt1 是不是 用户u的生日:true
System.out.println("dt1==用户u的生日:" + dtMD.equals(uBirth));
// #6. 获取当前时间 [HH:mm:ss.SSS]
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
LocalTime time = LocalTime.now();
System.out.println(time);
// #7. 增减时间 plus/minus
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
// dt1=2019-03-08
LocalDate dt1Plus2d = dt1.plusDays(2);
LocalDate dt1Plus2y = dt1.plusYears(2);
LocalDate dt1Plus2m = dt1.plusMonths(2);
System.out.println(dt1Plus2d); // 2019-03-10
System.out.println(dt1Plus2y); // 2021-03-08
System.out.println(dt1Plus2m); // 2019-05-08
// dt1=2019-03-08
LocalDate plus1w = dt1.plus(1, ChronoUnit.WEEKS);
LocalDate plus1d = dt1.plus(1, ChronoUnit.DAYS);
LocalDate plus18y = dt1.plus(18, ChronoUnit.YEARS);
LocalDate minus1y = dt1.minus(1, ChronoUnit.YEARS);
System.out.println(plus1w); // 2019-03-15
System.out.println(plus1d); // 2019-03-09
System.out.println(plus18y); // 2037-03-08
System.out.println(minus1y); // 2018-03-08
// #8. 日期dt1 早于/晚于 minus1y
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
// dt1=2019-03-08 minus1y=2018-03-08
System.out.println(dt1.isAfter(minus1y)); // true
System.out.println(dt1.isBefore(minus1y)); // false
// #9. 计算日期差
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
// dt1=2019-03-08 dt20190402
LocalDate dt20190402 = LocalDate.of(2019, 4, 2);
Period btPeriod = Period.between(dt1, dt20190402);
Period btPeriod2 = Period.between(dt1, dt20190402);
System.out.println(btPeriod); // P25D
System.out.println(btPeriod.getMonths()); // 0
System.out.println(btPeriod.getDays()); // 25
// 25 可见是标量, 不是矢量, 只计算差数
System.out.println(btPeriod2.getDays());
// #10. 时间戳Instant->java.util.Date[getTime()==toEpochMilli()]
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
Instant now = Instant.now(); // 2019-04-02T08:48:46.755Z
Date dtNow = Date.from(now); // Tue Apr 02 16:48:46 CST 2019
long millisInstant = now.toEpochMilli();
long millisDate = dtNow.getTime();
System.out.println(millisInstant); // 1554195038598
System.out.println(millisDate); // 1554195038598
// #11# ** 日期格式化
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
DateTimeFormatter pattern1 = DateTimeFormatter.ofPattern("yyyyMMdd-HH:mm:ss,SSS");
DateTimeFormatter pattern2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
/**
* 命题:--> 将 "20190215-22:10:30,333" 日期
* 格式化为 "yyyyMMdd-HH mm:ss.SSS" 字符串
* @.1. 字符串转对象LocalDateTime
* @.2. LocalDateTime对象转字符串
*/
String strDt = "20190215-22:10:30,333"; // @.1.
LocalDateTime dateTime = LocalDateTime.parse(strDt, pattern1);
String fmtDtString = dateTime.format(pattern2); // @.2.
System.out.println(dateTime); // 2019-02-15T22:10:30.333
System.out.println(fmtDtString); // 2019-02-15 22:10:30
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
}
}2. LocalDate: [yyyy-MM-dd]
LocalDate date = LocalDate.now();
LocalDate dt1 = LocalDate.of(2019, 3, 8);
LocalDate dt2 = LocalDate.of(2019, 3, 8);
3. LocalTime: [HH:mm:ss.SSS]
// #6. 获取当前时间 [HH:mm:ss.SSS]
System.out.println(“=-==-==-==-==-==-==-==-==-==-==”);
LocalTime time = LocalTime.now();
System.out.println(time);
4. MonthDay: [MMdd]=0308
// 生日:0308
MonthDay uBirth = MonthDay.of(3, 8);
MonthDay dtMD = MonthDay.from(dt1);
5. Period 日期差
Period btPeriod = Period.between(dt1, dt20190402);
Period btPeriod2 = Period.between(dt1, dt20190402);
6. 时间戳
// #10. 时间戳Instant->java.util.Date[getTime()==toEpochMilli()]
System.out.println(“=-==-==-==-==-==-==-==-==-==-==”);
Instant now = Instant.now(); // 2019-04-02T08:48:46.755Z
Date dtNow = Date.from(now); // Tue Apr 02 16:48:46 CST 2019
long millisInstant = now.toEpochMilli();
long millisDate = dtNow.getTime();
System.out.println(millisInstant); // 1554195038598
System.out.println(millisDate); // 1554195038598
7. 日期格式化
// #11# ** 日期格式化
System.out.println("=-==-==-==-==-==-==-==-==-==-==");
DateTimeFormatter pattern1 = DateTimeFormatter.ofPattern("yyyyMMdd-HH:mm:ss,SSS");
DateTimeFormatter pattern2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
/**
* 命题:--> 将 "20190215-22:10:30,333" 日期
* 格式化为 "yyyyMMdd-HH mm:ss.SSS" 字符串
* @.1. 字符串转对象LocalDateTime
* @.2. LocalDateTime对象转字符串
*/
String strDt = "20190215-22:10:30,333"; // @.1.
LocalDateTime dateTime = LocalDateTime.parse(strDt, pattern1);
String fmtDtString = dateTime.format(pattern2); // @.2.
System.out.println(dateTime); // 2019-02-15T22:10:30.333
System.out.println(fmtDtString); // 2019-02-15 22:10:30
System.out.println("=-==-==-==-==-==-==-==-==-==-==");转载请注明来源，欢迎对文章中的引用来源进行考证，欢迎指出任何有错误或不够清晰的表达。可以在下面评论区评论，也可以邮件至 hi@niewj.com
