【Java】【常用类】LocalDateTime 当前日期时间类 相关

LocalDate主要的三个API类：

java.time.LocalDate;
java.time.LocalDateTime;
java.time.LocalTime;

LocatDate对象获取：

@Test
void contextLoads() {
    // 获取方式
    LocalDate localDate = LocalDate.now();
    System.out.println(localDate);
    LocalDate localDate1 = LocalDate.of(2020, 5, 23);
    System.out.println(localDate1);
    // 2020-09-28
    // 2020-05-23
    int year = localDate.getYear(); // 取年
    int monthValue = localDate.getMonthValue(); // 取月
    Month month = localDate.getMonth(); // 取月的枚举对象
    int monthValue1 = month.getValue(); // 具体值可以通过该枚举对象获取
    // 除此之外Month还有一些获取其他信息的方法
    int maxDaysLength = month.maxLength(); // 该月的最大天数
    int minDaysLength = month.minLength(); // 该月的最小天数
    int dayOfMonth = localDate.getDayOfMonth(); // 按当月取天数
    int dayOfYear = localDate.getDayOfYear(); // 按本年取天数
    DayOfWeek dayOfWeek = localDate.getDayOfWeek(); // 按本周取天数？
    // 和月枚举对象一样，这里也是一个周枚举对象
    int value = dayOfWeek.getValue();
    System.out.println(dayOfWeek); // 打印为 MONDAY ....
}
private static void cryptTest() {
    final String PASSWORD = "123456";
    PasswordEncoder passwordEncoder = new BCryptPasswordEncoder();
    String encode = passwordEncoder.encode(PASSWORD);
    System.out.println(encode);
    boolean matches = passwordEncoder.matches(PASSWORD, encode);
    System.out.println(matches);
}

LocalDateTime & LocalTime：

@Test
void contextLoads() {
    LocalDateTime localDateTime1 = LocalDateTime.now();
    LocalDateTime localDateTime2 = LocalDateTime.of(2020, 2, 2, 13, 24, 52);
    System.out.println(localDateTime1); // 2020-09-28T16:01:48.248
    System.out.println(localDateTime2); // 2020-02-02T13:24:52

    LocalTime localTime1 = LocalTime.now();
    LocalTime localTime2 = LocalTime.of(20, 2, 2);
    System.out.println(localTime1); // 16:03:41.330
    System.out.println(localTime2); // 20:02:02

    int hour = localTime1.getHour();
    int minute = localTime1.getMinute();
    int second = localTime1.getSecond();
    int nano = localTime1.getNano();
    System.out.println("时 -> " + hour);         // 时 -> 16
    System.out.println("分 -> " + minute);       // 分 -> 6
    System.out.println("秒 -> " + second);       // 秒 -> 26
    System.out.println("Nano -> " + nano);      // Nano -> 206000000
}

GET方法

SET方法

增加时间

减少时间

public class DateTest {
    public static void main(String[] args) {
        LocalDate now1 = LocalDate.now();
        LocalTime now2 = LocalTime.now();
        LocalDateTime now3 = LocalDateTime.now();

        System.out.println("LocalDate.now() -> " + now1);
        System.out.println("LocalTime.now() -> " + now2);
        System.out.println("LocalDateTime.now() -> " + now3);
        /*
            LocalDate.now() -> 2020-04-19
            LocalTime.now() -> 21:16:03.854
            LocalDateTime.now() -> 2020-04-19T21:16:03.854
        */
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println("localDateTime.getDayOfWeek() -> " + localDateTime.getDayOfWeek() );     // 按周算天
        System.out.println("localDateTime.getDayOfMonth() -> " + localDateTime.getDayOfMonth() );   // 按月算天
        System.out.println("localDateTime.getDayOfYear() -> " + localDateTime.getDayOfYear() );     // 按年算天
        /*
            localDateTime.getDayOfWeek() -> SUNDAY
            localDateTime.getDayOfMonth() -> 19
            localDateTime.getDayOfYear() -> 110
         */
        System.out.println( localDateTime.getSecond()       );// 取秒
        System.out.println( localDateTime.getMinute()       );// 取分
        System.out.println( localDateTime.getHour()         );// 取时
        System.out.println( localDateTime.getMonth()        );// 取月 英文大写
        System.out.println( localDateTime.getMonthValue()   );// 取月 数值表示
        System.out.println( localDateTime.getYear()         );// 取年
        // set ×  with √
    }
}

instant 瞬时时间 ，精度达到纳秒级

public class DateTest {
    public static void main(String[] args) {
        Instant instant = Instant.now();
        System.out.println(instant);
        //  2020-04-19T13:47:58.712Z 本初子午线的标准时间

        // 我们是东八时区，添加8小时的偏移量
        OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));
        System.out.println(offsetDateTime);

        // 从实例获取毫秒数 时间戳
        long epochMilli = instant.toEpochMilli();
        System.out.println(epochMilli);

        // 通过时间戳注入产生instant实例
        Instant epochMilli1 = Instant.ofEpochMilli(epochMilli);
        System.out.println(epochMilli1);
    }
}

DateTimeFormatter

public class DateTest {
    public static void main(String[] args) {

        // 预定义的标准格式
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;

        // 事件对象
        LocalDateTime now = LocalDateTime.now();

        // 转换格式 日期 -> 字符串格式
        String format = dateTimeFormatter.format(now);

        // 格式
        System.out.println( now );
        System.out.println( format );

        // 日期 转 字符串格式
        TemporalAccessor parse = dateTimeFormatter.parse("2020-03-19T22:09:46.345");
        System.out.println(parse);

        DateTimeFormatter dateTimeFormatter1 = DateTimeFormatter.ofLocalizedDate(FormatStyle.FULL);
        // ofLocalizedDateTime();
        // ofLocalizedDate(); 按Date就支持FULL全格式
        // ofPattern("自定义格式"); "yyyy-MM-dd hh:mm:ss"

        // FormatStyle.FULL     2020年4月19日 星期日
        // FormatStyle.LONG     2020年4月19日 下午10时15分01秒
        // FormatStyle.MEDIUM   2020-4-19 22:14:28
        // FormatStyle.SHORT    20-4-19 下午10:16

        String format1 = dateTimeFormatter1.format(now);
        System.out.println(now);
        System.out.println(format1);

        TemporalAccessor parse1 = dateTimeFormatter1.parse(format1);
        System.out.println(parse1);
    }
}

案例，制作日历：

@Test
void contextLoads() {
    localDateCalendar();
}

private static void localDateCalendar() {
    LocalDate now = LocalDate.now();
    int year = now.getYear();
    int month = now.getMonth().getValue();
    int dayOfMonth = now.getDayOfMonth();

    // 设置这个月的第一天
    now = now.minusDays(dayOfMonth - 1);
    // 找到这一天为周几
    int value = now.getDayOfWeek().getValue();

    // 开始渲染控制台输出样式
    System.out.println("Mon Tue Wed Thu Fri Sat Sun");
    for (int i = 1; i < value; i++) System.out.print("   ");
    while (now.getMonthValue() == month) {
        System.out.printf("%3d", now.getDayOfMonth());
        if (now.getDayOfMonth() == dayOfMonth) System.out.print("*");
        else System.out.print(" ");
        now = now.plusDays(1);
        if (now.getDayOfWeek().getValue() == 1) System.out.println();
    }
    if (now.getDayOfWeek().getValue() != 1) System.out.println();
}

打印结果：

Mon Tue Wed Thu Fri Sat Sun
     1   2   3   4   5   6 
  7   8   9  10  11  12  13 
 14  15  16  17  18  19  20 
 21  22  23  24  25  26  27 
 28* 29  30 

其他API

ZoneId

ZoneDateTime

Clock

Duration

Period

TemporalAdjuster

TemporalAdjusters