获取当天、本周、本月开始与结束时的时间戳

1、获取当天开始与结束的时间戳

// 当天的 00:00:00
fun getStartOfDay(): Long {
    val calendar = Calendar.getInstance()
    val year = calendar.get(Calendar.YEAR)
    val month = calendar.get(Calendar.MONTH)
    val day = calendar.get(Calendar.DATE)
    calendar.set(year, month, day, 0, 0, 0)
    calendar.set(Calendar.MILLISECOND,0)
    return calendar.timeInMillis
}

// 当天的 23:59:59
fun getEndOfDay(): Long {
    val calendar = Calendar.getInstance()
    val year = calendar.get(Calendar.YEAR)
    val month = calendar.get(Calendar.MONTH)
    val day = calendar.get(Calendar.DATE)
    calendar.set(year, month, day, 23, 59, 59)
    calendar.set(Calendar.MILLISECOND,999)
    return calendar.timeInMillis
}

2、获取本周开始与结束的时间戳

主要参考：https://blog.youkuaiyun.com/zhuwentao2150/article/details/52084642

/**
 * 本周最开始时间戳（即那天的 00:00:00） - 以星期一为本周的第一天
 */
fun getStartOfWeek(): Long {
    val calendar = Calendar.getInstance()
    var dayOfWeek = calendar.get(Calendar. DAY_OF_WEEK) - 1
    if (dayOfWeek==0) dayOfWeek = 7
    calendar.add(Calendar.DATE, -dayOfWeek + 1)
    calendar.set(Calendar.HOUR_OF_DAY,0)// 注意与 HOUR 的区别
    calendar.set(Calendar.MINUTE,0)
    calendar.set(Calendar.SECOND,0)
    calendar.set(Calendar.MILLISECOND,0)
    return calendar.timeInMillis
}

/**
 * 本周结束的时间戳（即那天的 23:59:59） - 以星期一为本周的第一天
 */
fun getEndOfWeek(): Long {
    val calendar = Calendar.getInstance()
    var dayOfWeek = calendar.get(Calendar. DAY_OF_WEEK) - 1
    if (dayOfWeek==0) dayOfWeek = 7
    calendar.add(Calendar.DATE, -dayOfWeek + 7)
    calendar.set(Calendar.HOUR_OF_DAY,23)
    calendar.set(Calendar.MINUTE,59)
    calendar.set(Calendar.SECOND,59)
    calendar.set(Calendar.MILLISECOND,999)
    return calendar.timeInMillis
}

3、获取本月开始 (本月第一天) 与结束的时间戳

fun getStartOfMonth(): Long {
    val calendar = Calendar.getInstance()
    calendar.set(Calendar.DAY_OF_MONTH, 1)
    calendar.set(Calendar.HOUR_OF_DAY, 0)
    calendar.set(Calendar.MINUTE,0)
    calendar.set(Calendar.SECOND,0)
    calendar.set(Calendar.MILLISECOND,0)
    return calendar.timeInMillis
}

fun getEndOfMonth(): Long {
    val calendar = Calendar.getInstance()
    calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH))
    calendar.set(Calendar.HOUR_OF_DAY, 23)
    calendar.set(Calendar.MINUTE,59)
    calendar.set(Calendar.SECOND,59)
    calendar.set(Calendar.MILLISECOND,999)
    return calendar.timeInMillis
}