获取北京时间 日开始时间戳

以下

package com.tusmind.dsv.core.util;

public class DateTimeUtil {
	public static final long ONE_DAY_MILLIS = 24L*3600*1000;
	public static final long timeZone = 8L*3600*1000;
	public static long getDayStartTime(long timeStamp) {
		return timeStamp - (timeStamp+timeZone)%(ONE_DAY_MILLIS);
	}
	public static long getDayEndTime(long timeStamp) {
		return getDayStartTime(timeStamp)+ONE_DAY_MILLIS-1;
	}
	public static long getTodayStartTime() {
		return getDayStartTime(System.currentTimeMillis());
	}
	public static long getTodayEndTime() {
		return getDayEndTime(System.currentTimeMillis());
	}
	
	public static void main(String[] args) {
		System.out.println(System.currentTimeMillis());
		System.out.println(getDayStartTime(1520813975000L));
		System.out.println(getDayEndTime(System.currentTimeMillis()));
	}
//	1520846449466
//	1520784000000
//	1520870399999
	
//	1520810375000	7:19
//	1520813975000   8:19
}

核心是：

getDayStartTime(long timeStamp)

推导:

(timeStamp +timeZone)- (timeStamp+timeZone)%(ONE_DAY_MILLIS)-timeZone