线程安全的LocalDateTime的各种转换

1.将LocalDateTime转为自定义的时间格式的字符串

public static String getDateTimeAsString(LocalDateTime localDateTime, String format) {

　　DateTimeFormatter formatter = DateTimeFormatter.ofPattern(format);

　　return localDateTime.format(formatter);

}

2.将long类型的timestamp转为LocalDateTime

public static LocalDateTime getDateTimeOfTimestamp(long timestamp) {

　　 Instant instant = Instant.ofEpochMilli(timestamp);

　　ZoneId zone = ZoneId.systemDefault();

　　return LocalDateTime.ofInstant(instant, zone);

}

3.将LocalDateTime转为long类型的timestamp

　　public static long getTimestampOfDateTime(LocalDateTime localDateTime) {

　　ZoneId zone = ZoneId.systemDefault();

　　Instant instant = localDateTime.atZone(zone).toInstant();

　　return instant.toEpochMilli();

}

4.将某时间字符串转为自定义时间格式的LocalDateTime

public static LocalDateTime parseStringToDateTime(String time, String format) {

　　DateTimeFormatter df = DateTimeFormatter.ofPattern(format);

　　return LocalDateTime.parse(time, df);

}

5.附一个获取当日凌晨时间戳的方式

@Test
public void testSystem(){
   Calendar c = Calendar.getInstance();
   c.set(Calendar.HOUR_OF_DAY, 0);
   c.set(Calendar.MINUTE, 0);
   c.set(Calendar.SECOND, 0);
   c.set(Calendar.MILLISECOND, 0);
   long timeInMillis = c.getTimeInMillis();
   Instant instant = Instant.ofEpochMilli(timeInMillis);
   ZoneId zone = ZoneId.systemDefault();
   LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
   DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
   String format = format.format( localDateTime);
   System.out.println(format);
}

最后看懂这个代码， 就提升了
long now = System.currentTimeMillis() / 1000l;

long daySecond = 60 * 60 * 24;

long dayTime = now - (now + 8 * 3600) % daySecond;

long nowTime =System.currentTimeMillis();
long todayStartTime =nowTime - ((nowTime + TimeZone.getDefault().getRawOffset()) % (24 * 60 * 60 * 1000L));