Java8之前，时间都是使用Date类，但Date类缺点太多，使用起来很麻烦，Java8的LocalDateTime很好的解决了这个问题

一、LocalDateTime

• 获取当前时刻非常直观

public class Test {
    public static void main(String[] args) {
        final LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println("当前时间：" + localDateTime);
        System.out.println("年：" + localDateTime.getYear());
        System.out.println("月：" + localDateTime.getMonthValue());
        System.out.println("日：" + localDateTime.getDayOfMonth());
        System.out.println("时：" + localDateTime.getHour());
        System.out.println("分：" + localDateTime.getMinute());
        System.out.println("秒：" + localDateTime.getSecond());
    }
}

 

• 构造一个指定的日期非常方便

 @org.junit.Test
 public void test1() {
        final LocalDateTime localDateTime = LocalDateTime.of(2021, Month.MAY, 9, 8, 12, 12);
        System.out.println(localDateTime);
}

• 日期修改

  public void test2() {
        final LocalDateTime localDateTime = LocalDateTime.of(2021, Month.MAY, 9, 15, 34, 12);
        System.out.println("减去一天：" + localDateTime.minusDays(1).format(DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss")));
        System.out.println("修改年份：" + localDateTime.withYear(2022));
        System.out.println("减去一年：" + localDateTime.minusYears(1));
  }

• 格式化日期

    public void test3() {
        final LocalDateTime localDateTime = LocalDateTime.now();
        final String format1 = localDateTime.format(DateTimeFormatter.ISO_DATE);
        final String format2 = localDateTime.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
        final String format3 = localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss"));
        System.out.println(format1); // 2021-05-09
        System.out.println(format2); // 2021-05-09T16:15:35.236
        System.out.println(format3); // 2021-05-09 04:15:35
    }

Date和LocalDateTime的转换

/**
 * java.util.Date --> java.time.LocalDateTime
 *
 * @param date Date
 * @return LocalDateTime
 */
public static LocalDateTime dateToLocalDateTime(Date date) {
    return date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
}

/**
 * java.time.LocalDateTime --> java.util.Date  
 *
 * @param localDateTime LocalDateTime
 * @return Date
 */
public static Date localDateTimeToDate(LocalDateTime localDateTime) {
    return Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
}

• 转换示例 

    public LocalDateTime convertDateToLDT(Date date) {
        return date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime();
    }
    @org.junit.Test
    public void test4() {
        // 日期格式
        final DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        // 当前日期 Date 类型
        final LocalDateTime dateTime = convertDateToLDT(new Date());
        // LocalDataeTime 类型 格式化输出
        System.out.println(dateTime.format(dateTimeFormatter)); // 2021-05-09 05:15:43
    }