一.Quartz中cron 表達式分析：
quartz 官方源碼（org.quartz.CronExpression）解釋：
Cron expressions are comprised of 6 required fields and one optional field separated by white space. The fields respectively are described as follows:
（翻譯：Cron表達式由6個必填字段和一個由空格分隔的可選字段組成。 這些字段分別描述如下：）
| Field Name | Allowed Values | Allowed Special Characters | ||
|---|---|---|---|---|
Seconds |
0-59 |
, - * / |
||
Minutes |
0-59 |
, - * / |
||
Hours |
0-23 |
, - * / |
||
Day-of-month |
1-31 |
, - * ? / L W |
||
Month |
1-12 or JAN-DEC |
, - * / |
||
Day-of-Week |
1-7 or SUN-SAT |
, - * ? / L # |
||
Year (Optional) |
empty, 1970-2199 |
, - * / |
由上表格可見，Quartz中cron表達式可以由最多7個字段構成，即：秒、分、時、日、月、周、年，最后一個字段”年“則可以為空；
對於周幾，即 “Day-of-Week” 其值 1，2，3，4，5，6，7分別表示 “SUN,MON,TUE,WED,THU,FRI,SAT”；
二. SpringBoot schedule cron表達式分析：
解析cron expression的源碼（org.springframework.scheduling.support.CronSequenceGenerator.class）：
1 private void parse(String expression) throws IllegalArgumentException { 2 String[] fields = StringUtils.tokenizeToStringArray(expression, " "); 3 if (!areValidCronFields(fields)) { 4 throw new IllegalArgumentException(String.format( 5 "Cron expression must consist of 6 fields (found %d in \"%s\")", fields.length, expression)); 6 } 7 setNumberHits(this.seconds, fields[0], 0, 60); 8 setNumberHits(this.minutes, fields[1], 0, 60); 9 setNumberHits(this.hours, fields[2], 0, 24); 10 setDaysOfMonth(this.daysOfMonth, fields[3]); 11 setMonths(this.months, fields[4]); 12 setDays(this.daysOfWeek, replaceOrdinals(fields[5], "SUN,MON,TUE,WED,THU,FRI,SAT"), 8); 13 if (this.daysOfWeek.get(7)) { 14 // Sunday can be represented as 0 or 7 15 this.daysOfWeek.set(0); 16 this.daysOfWeek.clear(7); 17 } 18 }
重點看setDays方法，此方法轉換dayOfWeek的值，找到replaceOrdnal方法源碼：
1 /** 2 * Replace the values in the comma-separated list (case insensitive) 3 * with their index in the list. 4 * @return a new String with the values from the list replaced 5 */ 6 private String replaceOrdinals(String value, String commaSeparatedList) { 7 String[] list = StringUtils.commaDelimitedListToStringArray(commaSeparatedList); 8 for (int i = 0; i < list.length; i++) { 9 String item = list[i].toUpperCase(); 10 value = StringUtils.replace(value.toUpperCase(), item, "" + i); 11 } 12 return value; 13 }
上面的代碼直接將cronExpression字符串中的 "SUN,MON,TUE,WED,THU,FRI,SAT"分別替換成了”0，1，2，3，4，5，6“；
而且parse方法中注釋”// Sunday can be represented as 0 or 7” 即：周日均可用‘0’或’7‘表示。
所以對於springBoot schedule 其值 1，2，3，4，5，6，7分別表示 “MON,TUE,WED,THU,FRI,SAT,SUN”；0也表示SUN;