灵活，可靠和快速的分布式任务重试和分布式任务调度平台

/* * All content copyright Terracotta, Inc., unless otherwise indicated. All rights reserved. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy * of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations * under the License. * */ package com.aizuda.snailjob.common.core.util; import java.io.Serializable; import java.text.ParseException; import java.util.*; /** * Provides a parser and evaluator for unix-like cron expressions. Cron * expressions provide the ability to specify complex time combinations such as * &quot;At 8:00am every Monday through Friday&quot; or &quot;At 1:30am every * last Friday of the month&quot;. * <P> * Cron expressions are comprised of 6 required fields and one optional field * separated by white space. The fields respectively are described as follows: * * <table cellspacing="8"> * <tr> * <th align="left">Field Name</th> * <th align="left">&nbsp;</th> * <th align="left">Allowed Values</th> * <th align="left">&nbsp;</th> * <th align="left">Allowed Special Characters</th> * </tr> * <tr> * <td align="left"><code>Seconds</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>0-59</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * /</code></td> * </tr> * <tr> * <td align="left"><code>Minutes</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>0-59</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * /</code></td> * </tr> * <tr> * <td align="left"><code>Hours</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>0-23</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * /</code></td> * </tr> * <tr> * <td align="left"><code>Day-of-month</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>1-31</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * ? / L W</code></td> * </tr> * <tr> * <td align="left"><code>Month</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>0-11 or JAN-DEC</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * /</code></td> * </tr> * <tr> * <td align="left"><code>Day-of-Week</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>1-7 or SUN-SAT</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * ? / L #</code></td> * </tr> * <tr> * <td align="left"><code>Year (Optional)</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>empty, 1970-2199</code></td> * <td align="left">&nbsp;</th> * <td align="left"><code>, - * /</code></td> * </tr> * </table> * <P> * The '*' character is used to specify all values. For example, &quot;*&quot; * in the minute field means &quot;every minute&quot;. * <P> * The '?' character is allowed for the day-of-month and day-of-week fields. It * is used to specify 'no specific value'. This is useful when you need to * specify something in one of the two fields, but not the other. * <P> * The '-' character is used to specify ranges For example &quot;10-12&quot; in * the hour field means &quot;the hours 10, 11 and 12&quot;. * <P> * The ',' character is used to specify additional values. For example * &quot;MON,WED,FRI&quot; in the day-of-week field means &quot;the days Monday, * Wednesday, and Friday&quot;. * <P> * The '/' character is used to specify increments. For example &quot;0/15&quot; * in the seconds field means &quot;the seconds 0, 15, 30, and 45&quot;. And * &quot;5/15&quot; in the seconds field means &quot;the seconds 5, 20, 35, and * 50&quot;. Specifying '*' before the '/' is equivalent to specifying 0 is * the value to start with. Essentially, for each field in the expression, there * is a set of numbers that can be turned on or off. For seconds and minutes, * the numbers range from 0 to 59. For hours 0 to 23, for days of the month 0 to * 31, and for months 0 to 11 (JAN to DEC). The &quot;/&quot; character simply helps you turn * on every &quot;nth&quot; value in the given set. Thus &quot;7/6&quot; in the * month field only turns on month &quot;7&quot;, it does NOT mean every 6th * month, please note that subtlety. * <P> * The 'L' character is allowed for the day-of-month and day-of-week fields. * This character is short-hand for &quot;last&quot;, but it has different * meaning in each of the two fields. For example, the value &quot;L&quot; in * the day-of-month field means &quot;the last day of the month&quot; - day 31 * for January, day 28 for February on non-leap years. If used in the * day-of-week field by itself, it simply means &quot;7&quot; or * &quot;SAT&quot;. But if used in the day-of-week field after another value, it * means &quot;the last xxx day of the month&quot; - for example &quot;6L&quot; * means &quot;the last friday of the month&quot;. You can also specify an offset * from the last day of the month, such as "L-3" which would mean the third-to-last * day of the calendar month. <i>When using the 'L' option, it is important not to * specify lists, or ranges of values, as you'll get confusing/unexpected results.</i> * <P> * The 'W' character is allowed for the day-of-month field. This character * is used to specify the weekday (Monday-Friday) nearest the given day. As an * example, if you were to specify &quot;15W&quot; as the value for the * day-of-month field, the meaning is: &quot;the nearest weekday to the 15th of * the month&quot;. So if the 15th is a Saturday, the trigger will fire on * Friday the 14th. If the 15th is a Sunday, the trigger will fire on Monday the * 16th. If the 15th is a Tuesday, then it will fire on Tuesday the 15th. * However if you specify &quot;1W&quot; as the value for day-of-month, and the * 1st is a Saturday, the trigger will fire on Monday the 3rd, as it will not * 'jump' over the boundary of a month's days. The 'W' character can only be * specified when the day-of-month is a single day, not a range or list of days. * <P> * The 'L' and 'W' characters can also be combined for the day-of-month * expression to yield 'LW', which translates to &quot;last weekday of the * month&quot;. * <P> * The '#' character is allowed for the day-of-week field. This character is * used to specify &quot;the nth&quot; XXX day of the month. For example, the * value of &quot;6#3&quot; in the day-of-week field means the third Friday of * the month (day 6 = Friday and &quot;#3&quot; = the 3rd one in the month). * Other examples: &quot;2#1&quot; = the first Monday of the month and * &quot;4#5&quot; = the fifth Wednesday of the month. Note that if you specify * &quot;#5&quot; and there is not 5 of the given day-of-week in the month, then * no firing will occur that month. If the '#' character is used, there can * only be one expression in the day-of-week field (&quot;3#1,6#3&quot; is * not valid, since there are two expressions). * <P> * <!--The 'C' character is allowed for the day-of-month and day-of-week fields. * This character is short-hand for "calendar". This means values are * calculated against the associated calendar, if any. If no calendar is * associated, then it is equivalent to having an all-inclusive calendar. A * value of "5C" in the day-of-month field means "the first day included by the * calendar on or after the 5th". A value of "1C" in the day-of-week field * means "the first day included by the calendar on or after Sunday".--> * <P> * The legal characters and the names of months and days of the week are not * case sensitive. * * <p> * <b>NOTES:</b> * <