LocalDateTime 代替 Date

背景

http://devgou.com/article/Java-Date/

• Date如果不格式化，打印出的日期可读性差
  Tue Sep 10 09:34:04 CST 2019
• 使用SimpleDateFormat对时间进行格式化，但SimpleDateFormat是线程不安全的
• Date对时间处理比较麻烦，比如想获取某年、某月、某星期。（getYear、getMonth已弃用）

使用java8新的api，LocalDateTime

LocalDate，只有年月日

获取当前时间

LocalDate localDate = LocalDate.now();
System.out.println(localDate); //2020-03-23

构造指定的年月日

LocalDate localDate = LocalDate.of(2020, 3, 23);
System.out.println(localDate); //2020-03-23

获取年月日

LocalDate localDate = LocalDate.of(2020, 3, 23);
        int year = localDate.getYear();
        Month month = localDate.getMonth();
        int day = localDate.getDayOfMonth();
        DayOfWeek dayOfWeek = localDate.getDayOfWeek();

        System.out.println(year); //2020
        System.out.println(month.getValue()); //3
        System.out.println(day); //23
        System.out.println(dayOfWeek.getValue()); //1

LocalTime，只有时分秒

当前日期

LocalTime localTime1 = LocalTime.now();
System.out.println(localTime); //20:30:52.620

创建指定的日期

LocalTime localTime = LocalTime.of(20, 30, 52);
System.out.println(localTime); //20:30:52.620

获取时分秒

LocalTime localTime = LocalTime.of(20, 30, 52,200);
System.out.println(localTime.getHour()); // 20
System.out.println(localTime.getMinute()); // 30
System.out.println(localTime.getSecond()); //52
System.out.println(localTime.getNano()); // 200

LocalDateTime，相当于前两个结合

构造函数

LocalDateTime localDateTime = LocalDateTime.now(); 
LocalDateTime localDateTime1 = LocalDateTime.of(localDate, localTime); 
LocalDateTime localDateTime3 = localDate.atTime(localTime);
 LocalDateTime localDateTime4 = localTime.atDate(localDate);

获取localDate

LocalDate localDate = localDateTime.toLocalDate();

获取LocalTime

LocalTime localTime = localDateTime.toLocalTime();

LocalDateTime增加日期

LocalDateTime localDateTime = LocalDateTime.now();
LocalDateTime localDateTime = LocalDateTime.now();
localDateTime.minusDays(1); //减少一天
localDateTime.plusDays(1); // 增加一天

localDateTime = localDateTime.withYear(2020); //修改为2020

格式化时间

LocalDate localDate = LocalDate.of(2020, 3, 23);
String s1 = localDate.format(DateTimeFormatter.BASIC_ISO_DATE);
String s2 = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE);
DateTimeFormatter dateTimeFormatter =   DateTimeFormatter.ofPattern("dd/MM/yyyy");
String s3 = localDate.format(dateTimeFormatter);

System.out.println(s1); //20200323
System.out.println(s2); //2020-03-23
System.out.println(s3); //23/03/2020

解析时间

LocalDate localDate1 = LocalDate.parse("20200323", DateTimeFormatter.BASIC_ISO_DATE);
LocalDate localDate2 = LocalDate.parse("2020-03-23", DateTimeFormatter.ISO_LOCAL_DATE);