About the most common methods and time conversion methods of LocalDateTime

public static LocalDateTime parseStringToDateTime(String time, String format) {
DateTimeFormatter df = (format);
return (time, df);
}

public static String getDateTimeToString(LocalDateTime localDateTime, String format) {
DateTimeFormatter formatter = (format);
return (formatter);
}

String utc = getUTCMillisecondFromTimestamp(1539718265123);
(utc);

Output：2018-10-16T19:31:05.123Z

String utc = getUTCMillisecondFromTimestamp(1539718265000);
(utc);

Output：2018-10-16T19:31:05Z

/**
	  * Convert UTC timestamp to UTC string (exactly to seconds)
	  *
	  * @param timestamp
	  * @return
	  */
	public static String getUTCStrFromTimestamp(long timestamp) {
		DateTimeFormatter formatter = ("yyyy-MM-dd'T'HH:mm:ss'Z'");
		// Beijing time: ("UTC+8"); system default time: ()		LocalDateTime localDateTime = ((timestamp), ("UTC"));
		String utc = (formatter);
		return utc;
	}

String utc = getUTCStrFromTimestamp(1539718265123);
(utc);

Output：2018-10-16T19:31:05Z

	/**
	  * Convert the timestamp to a UTC string (if milliseconds are 000, no milliseconds are displayed, and if milliseconds are not 000, no milliseconds are displayed)
	  *
	  * Return format: 2018-10-16T19:31:05.123Z
	  *
	  * @param timestamp
	  * @return
	  */
	public static String getUTCMillisecondFromTimestamp(long timestamp) {
		Instant instant = (timestamp);
		String utcString = ();
		return utcString;
	}

DateTimeFormatter formatter = ("yyyy-MM-dd'T'HH:mm:ss'Z'");

String startTime = ().withHour(0).withMinute(0).withSecond(0).withNano(0).format(formatter);

String endTime = ().withHour(23).withMinute(59).withSecond(59).withNano(999_999_999).format(formatter);

/**
	  * Return to the last day of the target month
	  *
	  * @param sourceDate Target month
	  * @param monthOffset Month Offset
	  * @return
	  */
	private LocalDate getLastDateOfMonth(LocalDate sourceDate, int monthOffset) {
		return (monthOffset).with(());
	}

LocalDate date = (2021, 4, 20);
LocalDateTime startTime = (date, );
LocalDateTime endTime = (date, );

/**
	  * Get a ten-minute starting time stamp of a (millisecond) timestamp
	  *
	  * For example: Enter the timestamp of 1534930875000 (2018-08-22 17:41:15) returns the timestamp of 1534930800000 (2018-08-22 17:40:00)
	  *
	  * @param timestrap
	  *
	  *
	  * @return
	  */
	public static long getTenMinuteStartTimestrap(long timestamp) {
		LocalDateTime localDateTime = getLocalDateTimeByTimestamp(timestamp);
		int minute = ();
		// The number of single digits in minutes is set to 0		int minute_floor = minute / 10 * 10;
		LocalDateTime startLocalDateTime = (minute_floor).withSecond(0).withNano(0);
		long startTimestamp = getTimestampByLocalDateTime(startLocalDateTime);
		return startTimestamp;
	}

	/**
	  * Long millisecond timestamp to LocalDateTime
	  */
	public static LocalDateTime getLocalDateTimeByTimestamp(long timestamp) {
		Instant instant = (timestamp);
		LocalDateTime localDateTime = (instant, );
		return localDateTime;
	}

	/**
	  * Get LocalDateTime based on millisecond timestamp
	  * @param localDateTime
	  * @return
	  */
	public static long getTimestampByLocalDateTime(LocalDateTime localDateTime) {
		long timestamp = (("UTC")).toInstant().toEpochMilli();
		return timestamp;
	}

/**
	  * Timestamp is converted to local date according to time zone
	  * @param timestamp
	  * @param timezone
	  * @return
	  */
	public static Date getLocalDateByTimezone(long timestamp, int timezone) {
		Instant instant = (timestamp);
		LocalDateTime localDateTime = (instant, );
		// Local time		LocalDateTime localDate = (timezone);
		DateTimeFormatter df = ("yyyy-MM-dd'T'HH:mm:ss'Z'");
		String localDateTimeStr = (localDate);
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
		Date date = null;
		try {
			date = (localDateTimeStr);
		} catch (ParseException e) {
			();
		}
		return date;
	}

Date date = (().atZone(()).toInstant());

Date todayDate = new Date();
LocalDateTime ldt = ()
        .atZone( () )
        .toLocalDateTime();

long second = (1636338645000L).getEpochSecond();

long second = (1636338645L).toEpochMilli();