The trigger str used to build the cronTrigger instance
Decode the cron Time string
The cron time string, like: 1,2 or 1-3
A sorted array, like [1,2,3]
Decude the cronTrigger string to arrays
The cronTimeStr need to decode, like "0 12 * 3"
The array to represent the cronTimer
Get the current excuteTime of trigger
Caculate the next valid cronTime after the given time
The nearest valid time after the given time point
The constructor of the CronTrigger