常用的定时任务组件有 Quartz.Net 和 Hangfire 两种，这两种是使用人数比较多的定时任务组件，个人以前也是使用的 Hangfire ，慢慢的发现自己想要的其实只是一个能够根据 Cron 表达式来定时执行函数的功能，Quartz.Net 和 Hangfire 虽然都能实现这个目的，但是他们都只用来实现 Cron表达式解析定时执行函数就显得太笨重了，所以想着以 解析 Cron表达式定期执行函数为目的，编写了下面的一套逻辑。
首先为了解析 Cron表达式，我们需要一个CronHelper ,代码如下
using System.Globalization; using System.Text; using System.Text.RegularExpressions; namespace Common { public class CronHelper { ////// 获取当前时间之后下一次触发时间 /// /// /// public static DateTimeOffset GetNextOccurrence(string cronExpression) { return GetNextOccurrence(cronExpression, DateTimeOffset.UtcNow); } /// /// 获取给定时间之后下一次触发时间 /// /// /// /// public static DateTimeOffset GetNextOccurrence(string cronExpression, DateTimeOffset afterTimeUtc) { return new CronExpression(cronExpression).GetTimeAfter(afterTimeUtc)!.Value; } /// /// 获取当前时间之后N次触发时间 /// /// /// /// public static List GetNextOccurrences(string cronExpression, int count) { return GetNextOccurrences(cronExpression, DateTimeOffset.UtcNow, count); } /// /// 获取给定时间之后N次触发时间 /// /// /// /// public static List GetNextOccurrences(string cronExpression, DateTimeOffset afterTimeUtc, int count) { CronExpression cron = new(cronExpression); List dateTimeOffsets = new(); for (int i = 0; i < count; i++) { afterTimeUtc = cron.GetTimeAfter(afterTimeUtc)!.Value; dateTimeOffsets.Add(afterTimeUtc); } return dateTimeOffsets; } private class CronExpression { private const int Second = 0; private const int Minute = 1; private const int Hour = 2; private const int DayOfMonth = 3; private const int Month = 4; private const int DayOfWeek = 5; private const int Year = 6; private const int AllSpecInt = 99; private const int NoSpecInt = 98; private const int AllSpec = AllSpecInt; private const int NoSpec = NoSpecInt; private SortedSet<int> seconds = null!; private SortedSet<int> minutes = null!; private SortedSet<int> hours = null!; private SortedSet<int> daysOfMonth = null!; private SortedSet<int> months = null!; private SortedSet<int> daysOfWeek = null!; private SortedSet<int> years = null!; private bool lastdayOfWeek; private int everyNthWeek; private int nthdayOfWeek; private bool lastdayOfMonth; private bool nearestWeekday; private int lastdayOffset; private static readonly Dictionary<string, int> monthMap = new Dictionary<string, int>(20); private static readonly Dictionary<string, int> dayMap = new Dictionary<string, int>(60); private static readonly int MaxYear = DateTime.Now.Year + 100; private static readonly char[] splitSeparators = { ' ', '\t', '\r', '\n' }; private static readonly char[] commaSeparator = { ',' }; private static readonly Regex regex = new Regex("^L-[0-9]*[W]?", RegexOptions.Compiled); private static readonly TimeZoneInfo timeZoneInfo = TimeZoneInfo.Local; public CronExpression(string cronExpression) { if (monthMap.Count == 0) { monthMap.Add("JAN", 0); monthMap.Add("FEB", 1); monthMap.Add("MAR", 2); monthMap.Add("APR", 3); monthMap.Add("MAY", 4); monthMap.Add("JUN", 5); monthMap.Add("JUL", 6); monthMap.Add("AUG", 7); monthMap.Add("SEP", 8); monthMap.Add("OCT", 9); monthMap.Add("NOV", 10); monthMap.Add("DEC", 11); dayMap.Add("SUN", 1); dayMap.Add("MON", 2); dayMap.Add("TUE", 3); dayMap.Add("WED", 4); dayMap.Add("THU", 5); dayMap.Add("FRI", 6); dayMap.Add("SAT", 7); } if (cronExpression == null) { throw new ArgumentException("cronExpression 不能为空"); } CronExpressionString = CultureInfo.InvariantCulture.TextInfo.ToUpper(cronExpression); BuildExpression(CronExpressionString); } /// /// 构建表达式 /// /// /// private void BuildExpression(string expression) { try { seconds ??= new SortedSet<int>(); minutes ??= new SortedSet<int>(); hours ??= new SortedSet<int>(); daysOfMonth ??= new SortedSet<int>(); months ??= new SortedSet<int>(); daysOfWeek ??= new SortedSet<int>(); years ??= new SortedSet<int>(); int exprOn = Second; string[] exprsTok = expression.Split(splitSeparators, StringSplitOptions.RemoveEmptyEntries); foreach (string exprTok in exprsTok) { string expr = exprTok.Trim(); if (expr.Length == 0) { continue; } if (exprOn > Year) { break; } if (exprOn == DayOfMonth && expr.IndexOf('L') != -1 && expr.Length > 1 && expr.IndexOf(",", StringComparison.Ordinal) >= 0) { throw new FormatException("不支持在月份的其他日期指定“L”和“LW”"); } if (exprOn == DayOfWeek && expr.IndexOf('L') != -1 && expr.Length > 1 && expr.IndexOf(",", StringComparison.Ordinal) >= 0) { throw new FormatException("不支持在一周的其他日期指定“L”"); } if (exprOn == DayOfWeek && expr.IndexOf('#') != -1 && expr.IndexOf('#', expr.IndexOf('#') + 1) != -1) { throw new FormatException("不支持指定多个“第N”天。"); } string[] vTok = expr.Split(commaSeparator); foreach (string v in vTok) { StoreExpressionVals(0, v, exprOn); } exprOn++; } if (exprOn <= DayOfWeek) { throw new FormatException("表达式意料之外的结束。"); } if (exprOn <= Year) { StoreExpressionVals(0, "*", Year); } var dow = GetSet(DayOfWeek); var dom = GetSet(DayOfMonth); bool dayOfMSpec = !dom.Contains(NoSpec); bool dayOfWSpec = !dow.Contains(NoSpec); if (dayOfMSpec && !dayOfWSpec) { // skip } else if (dayOfWSpec && !dayOfMSpec) { // skip } else { throw new FormatException("不支持同时指定星期和日参数。"); } } catch (FormatException) { throw; } catch (Exception e) { throw new FormatException($"非法的 cron 表达式格式 ({e.Message})", e); } } /// /// Stores the expression values. /// /// The position. /// The string to traverse. /// The type of value. /// private int StoreExpressionVals(int pos, string s, int type) { int incr = 0; int i = SkipWhiteSpace(pos, s); if (i >= s.Length) { return i; } char c = s[i]; if (c >= 'A' && c <= 'Z' && !s.Equals("L") && !s.Equals("LW") && !regex.IsMatch(s)) { string sub = s.Substring(i, 3); int sval; int eval = -1; if (type == Month) { sval = GetMonthNumber(sub) + 1; if (sval <= 0) { throw new FormatException($"无效的月份值：'{sub}'"); } if (s.Length > i + 3) { c = s[i + 3]; if (c == '-') { i += 4; sub = s.Substring(i, 3); eval = GetMonthNumber(sub) + 1; if (eval <= 0) { throw new FormatException( $"无效的月份值： '{sub}'"); } } } } else if (type == DayOfWeek) { sval = GetDayOfWeekNumber(sub); if (sval < 0) { throw new FormatException($"无效的星期几值： '{sub}'"); } if (s.Length > i + 3) { c = s[i + 3]; if (c == '-') { i += 4; sub = s.Substring(i, 3); eval = GetDayOfWeekNumber(sub); if (eval < 0) { throw new FormatException( $"无效的星期几值： '{sub}'"); } } else if (c == '#') { try { i += 4; nthdayOfWeek = Convert.ToInt32(s.Substring(i), CultureInfo.InvariantCulture); if (nthdayOfWeek is < 1 or > 5) { throw new FormatException("周的第n天小于1或大于5"); } } catch (Exception) { throw new FormatException("1 到 5 之间的数值必须跟在“#”选项后面"); } } else if (c == '/') { try { i += 4; everyNthWeek = Convert.ToInt32(s.Substring(i), CultureInfo.InvariantCulture); if (everyNthWeek is < 1 or > 5) { throw new FormatException("每个星期<1或>5"); } } catch (Exception) { throw new FormatException("1 到 5 之间的数值必须跟在 '/' 选项后面"); } } else if (c == 'L') { lastdayOfWeek = true; i++; } else { throw new FormatException($"此位置的非法字符：'{sub}'"); } } } else { throw new FormatException($"此位置的非法字符：'{sub}'"); } if (eval != -1) { incr = 1; } AddToSet(sval, eval, incr, type); return i + 3; } if (c == '?') { i++; if (i + 1 < s.Length && s[i] != ' ' && s[i + 1] != '\t') { throw new FormatException("'?' 后的非法字符: " + s[i]); } if (type != DayOfWeek && type != DayOfMonth) { throw new FormatException( "'?' 只能为月日或周日指定。"); } if (type == DayOfWeek && !lastdayOfMonth) { int val = daysOfMonth.LastOrDefault(); if (val == NoSpecInt) { throw new FormatException( "'?' 只能为月日或周日指定。"); } } AddToSet(NoSpecInt, -1, 0, type); return i; } var startsWithAsterisk = c == '*'; if (startsWithAsterisk || c == '/') { if (startsWithAsterisk && i + 1 >= s.Length) { AddToSet(AllSpecInt, -1, incr, type); return i + 1; } if (c == '/' && (i + 1 >= s.Length || s[i + 1] == ' ' || s[i + 1] == '\t')) { throw new FormatException("'/' 后面必须跟一个整数。"); } if (startsWithAsterisk) { i++; } c = s[i]; if (c == '/') { // is an increment specified? i++; if (i >= s.Length) { throw new FormatException("字符串意外结束。"); } incr = GetNumericValue(s, i); i++; if (incr > 10) { i++; } CheckIncrementRange(incr, type); } else { if (startsWithAsterisk) { throw new FormatException("星号后的非法字符：" + s); } incr = 1; } AddToSet(AllSpecInt, -1, incr, type); return i; } if (c == 'L') { i++; if (type == DayOfMonth) { lastdayOfMonth = true; } if (type == DayOfWeek) { AddToSet(7, 7, 0, type); } if (type == DayOfMonth && s.Length > i) { c = s[i]; if (c == '-') { ValueSet vs = GetValue(0, s, i + 1); lastdayOffset = vs.theValue; if (lastdayOffset > 30) { throw new FormatException("与最后一天的偏移量必须 <= 30"); } i = vs.pos; } if (s.Length > i) { c = s[i]; if (c == 'W') { nearestWeekday = true; i++; } } } return i; } if (c >= '0' && c <= '9') { int val = Convert.ToInt32(c.ToString(), CultureInfo.InvariantCulture); i++; if (i >= s.Length) { AddToSet(val, -1, -1, type); } else { c = s[i]; if (c >= '0' && c <= '9') { ValueSet vs = GetValue(val, s, i); val = vs.theValue; i = vs.pos; } i = CheckNext(i, s, val, type); return i; } } else { throw new FormatException($"意外字符：{c}"); } return i; } // ReSharper disable once UnusedParameter.Local private static void CheckIncrementRange(int incr, int type) { if (incr > 59 && (type == Second || type == Minute)) { throw new FormatException($"增量 > 60 : {incr}"); } if (incr > 23 && type == Hour) { throw new FormatException($"增量 > 24 : {incr}"); } if (incr > 31 && type == DayOfMonth) { throw new FormatException($"增量 > 31 : {incr}"); } if (incr > 7 && type == DayOfWeek) { throw new FormatException($"增量 > 7 : {incr}"); } if (incr > 12 && type == Month) { throw new FormatException($"增量 > 12 : {incr}"); } } /// /// Checks the next value. /// /// The position. /// The string to check. /// The value. /// The type to search. /// private int CheckNext(int pos, string s, int val, int type) { int end = -1; int i = pos; if (i >= s.Length) { AddToSet(val, end, -1, type); return i; } char c = s[pos]; if (c == 'L') { if (type == DayOfWeek) { if (val < 1 || val > 7) { throw new FormatException("星期日值必须介于1和7之间"); } lastdayOfWeek = true; } else { throw new FormatException($"'L' 选项在这里无效。(位置={i})"); } var data = GetSet(type); data.Add(val); i++; return i; } if (c == 'W') { if (type == DayOfMonth) { nearestWeekday = true; } else { throw new FormatException($"'W' 选项在这里无效。 (位置={i})"); } if (val > 31) { throw new FormatException("'W' 选项对于大于 31 的值（一个月中的最大天数）没有意义"); } var data = GetSet(type); data.Add(val); i++; return i; } if (c == '#') { if (type != DayOfWeek) { throw new FormatException($"'#' 选项在这里无效。 (位置={i})"); } i++; try { nthdayOfWeek = Convert.ToInt32(s.Substring(i), CultureInfo.InvariantCulture); if (nthdayOfWeek is < 1 or > 5) { throw new FormatException("周的第n天小于1或大于5"); } } catch (Exception) { throw new FormatException("1 到 5 之间的数值必须跟在“#”选项后面"); } var data = GetSet(type); data.Add(val); i++; return i; } if (c == 'C') { if (type == DayOfWeek) { } else if (type == DayOfMonth) { } else { throw new FormatException($"'C' 选项在这里无效。(位置={i})"); } var data = GetSet(type); data.Add(val); i++; return i; } if (c == '-') { i++; c = s[i]; int v = Convert.ToInt32(c.ToString(), CultureInfo.InvariantCulture); end = v; i++; if (i >= s.Length) { AddToSet(val, end, 1, type); return i; } c = s[i]; if (c >= '0' && c <= '9') { ValueSet vs = GetValue(v, s, i); int v1 = vs.theValue; end = v1; i = vs.pos; } if (i < s.Length && s[i] == '/') { i++; c = s[i]; int v2 = Convert.ToInt32(c.ToString(), CultureInfo.InvariantCulture); i++; if (i >= s.Length) { AddToSet(val, end, v2, type); return i; } c = s[i]; if (c >= '0' && c <= '9') { ValueSet vs = GetValue(v2, s, i); int v3 = vs.theValue; AddToSet(val, end, v3, type); i = vs.pos; return i; } AddToSet(val, end, v2, type); return i; } AddToSet(val, end, 1, type); return i; } if (c == '/') { if (i + 1 >= s.Length || s[i + 1] == ' ' || s[i + 1] == '\t') { throw new FormatException("\'/\' 后面必须跟一个整数。"); } i++; c = s[i]; int v2 = Convert.ToInt32(c.ToString(), CultureInfo.InvariantCulture); i++; if (i >= s.Length) { CheckIncrementRange(v2, type); AddToSet(val, end, v2, type); return i; } c = s[i]; if (c >= '0' && c <= '9') { ValueSet vs = GetValue(v2, s, i); int v3 = vs.theValue; CheckIncrementRange(v3, type); AddToSet(val, end, v3, type); i = vs.pos; return i; } throw new FormatException($"意外的字符 '{c}' 后 '/'"); } AddToSet(val, end, 0, type); i++; return i; } /// /// Gets the cron expression string. /// /// The cron expression string. private static string CronExpressionString; /// /// Skips the white space. /// /// The i. /// The s. /// private static int SkipWhiteSpace(int i, string s) { for (; i < s.Length && (s[i] == ' ' || s[i] == '\t'); i++) { } return i; } /// /// Finds the next white space. /// /// The i. /// The s. /// private static int FindNextWhiteSpace(int i, string s) { for (; i < s.Length && (s[i] != ' ' || s[i] != '\t'); i++) { } return i; } /// /// Adds to set. /// /// The val. /// The end. /// The incr. /// The type. private void AddToSet(int val, int end, int incr, int type) { var data = GetSet(type); if (type == Second || type == Minute) { if ((val < 0 || val > 59 || end > 59) && val != AllSpecInt) { throw new FormatException("分钟和秒值必须介于0和59之间"); } } else if (type == Hour) { if ((val < 0 || val > 23 || end > 23) && val != AllSpecInt) { throw new FormatException("小时值必须介于0和23之间"); } } else if (type == DayOfMonth) { if ((val < 1 || val > 31 || end > 31) && val != AllSpecInt && val != NoSpecInt) { throw new FormatException("月日值必须介于1和31之间"); } } else if (type == Month) { if ((val < 1 || val > 12 || end > 12) && val != AllSpecInt) { throw new FormatException("月份值必须介于1和12之间"); } } else if (type == DayOfWeek) { if ((val == 0 || val > 7 || end > 7) && val != AllSpecInt && val != NoSpecInt) { throw new FormatException("星期日值必须介于1和7之间"); } } if ((incr == 0 || incr == -1) && val != AllSpecInt) { if (val != -1) { data.Add(val); } else { data.Add(NoSpec); } return; } int startAt = val; int stopAt = end; if (val == AllSpecInt && incr <= 0) { incr = 1; data.Add(AllSpec); } if (type == Second || type == Minute) { if (stopAt == -1) { stopAt = 59; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 0; } } else if (type == Hour) { if (stopAt == -1) { stopAt = 23; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 0; } } else if (type == DayOfMonth) { if (stopAt == -1) { stopAt = 31; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 1; } } else if (type == Month) { if (stopAt == -1) { stopAt = 12; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 1; } } else if (type == DayOfWeek) { if (stopAt == -1) { stopAt = 7; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 1; } } else if (type == Year) { if (stopAt == -1) { stopAt = MaxYear; } if (startAt == -1 || startAt == AllSpecInt) { startAt = 1970; } } int max = -1; if (stopAt < startAt) { switch (type) { case Second: max = 60; break; case Minute: max = 60; break; case Hour: max = 24; break; case Month: max = 12; break; case DayOfWeek: max = 7; break; case DayOfMonth: max = 31; break; case Year: throw new ArgumentException("开始年份必须小于停止年份"); default: throw new ArgumentException("遇到意外的类型"); } stopAt += max; } for (int i = startAt; i <= stopAt; i += incr) { if (max == -1) { data.Add(i); } else { int i2 = i % max; if (i2 == 0 && (type == Month || type == DayOfWeek || type == DayOfMonth)) { i2 = max; } data.Add(i2); } } } /// /// Gets the set of given type. /// /// The type of set to get. /// private SortedSet<int> GetSet(int type) { switch (type) { case Second: return seconds; case Minute: return minutes; case Hour: return hours; case DayOfMonth: return daysOfMonth; case Month: return months; case DayOfWeek: return daysOfWeek; case Year: return years; default: throw new ArgumentOutOfRangeException(); } } /// /// Gets the value. /// /// The v. /// The s. /// The i. /// private static ValueSet GetValue(int v, string s, int i) { char c = s[i]; StringBuilder s1 = new StringBuilder(v.ToString(CultureInfo.InvariantCulture)); while (c >= '0' && c <= '9') { s1.Append(c); i++; if (i >= s.Length) { break; } c = s[i]; } ValueSet val = new ValueSet(); if (i < s.Length) { val.pos = i; } else { val.pos = i + 1; } val.theValue = Convert.ToInt32(s1.ToString(), CultureInfo.InvariantCulture); return val; } /// /// Gets the numeric value from string. /// /// The string to parse from. /// The i. /// private static int GetNumericValue(string s, int i) { int endOfVal = FindNextWhiteSpace(i, s); string val = s.Substring(i, endOfVal - i); return Convert.ToInt32(val, CultureInfo.InvariantCulture); } /// /// Gets the month number. /// /// The string to map with. /// private static int GetMonthNumber(string s) { if (monthMap.ContainsKey(s)) { return monthMap[s]; } return -1; } /// /// Gets the day of week number. /// /// The s. /// private static int GetDayOfWeekNumber(string s) { if (dayMap.ContainsKey(s)) { return dayMap[s]; } return -1; } /// /// 在给定时间之后获取下一个触发时间。 /// /// 开始搜索的 UTC 时间。 /// public DateTimeOffset? GetTimeAfter(DateTimeOffset afterTimeUtc) { // 向前移动一秒钟，因为我们正在计算时间*之后* afterTimeUtc = afterTimeUtc.AddSeconds(1); // CronTrigger 不处理毫秒 DateTimeOffset d = CreateDateTimeWithoutMillis(afterTimeUtc); // 更改为指定时区 d = TimeZoneInfo.ConvertTime(d, timeZoneInfo); bool gotOne = false; //循环直到我们计算出下一次，或者我们已经过了 endTime while (!gotOne) { SortedSet<int> st; int t; int sec = d.Second; st = seconds.GetViewBetween(sec, 9999999); if (st.Count > 0) { sec = st.First(); } else { sec = seconds.First(); d = d.AddMinutes(1); } d = new DateTimeOffset(d.Year, d.Month, d.Day, d.Hour, d.Minute, sec, d.Millisecond, d.Offset); int min = d.Minute; int hr = d.Hour; t = -1; st = minutes.GetViewBetween(min, 9999999); if (st.Count > 0) { t = min; min = st.First(); } else { min = minutes.First(); hr++; } if (min != t) { d = new DateTimeOffset(d.Year, d.Month, d.Day, d.Hour, min, 0, d.Millisecond, d.Offset); d = SetCalendarHour(d, hr); continue; } d = new DateTimeOffset(d.Year, d.Month, d.Day, d.Hour, min, d.Second, d.Millisecond, d.Offset); hr = d.Hour; int day = d.Day; t = -1; st = hours.GetViewBetween(hr, 9999999); if (st.Count > 0) { t = hr; hr = st.First(); } else { hr = hours.First(); day++; } if (hr != t) { int daysInMonth = DateTime.DaysInMonth(d.Year, d.Month); if (day > daysInMonth) { d = new DateTimeOffset(d.Year, d.Month, daysInMonth, d.Hour, 0, 0, d.Millisecond, d.Offset).AddDays(day - daysInMonth); } else { d = new DateTimeOffset(d.Year, d.Month, day, d.Hour, 0, 0, d.Millisecond, d.Offset); } d = SetCalendarHour(d, hr); continue; } d = new DateTimeOffset(d.Year, d.Month, d.Day, hr, d.Minute, d.Second, d.Millisecond, d.Offset); day = d.Day; int mon = d.Month; t = -1; int tmon = mon; bool dayOfMSpec = !daysOfMonth.Contains(NoSpec); bool dayOfWSpec = !daysOfWeek.Contains(NoSpec); if (dayOfMSpec && !dayOfWSpec) { // 逐月获取规则 st = daysOfMonth.GetViewBetween(day, 9999999); bool found = st.Any(); if (lastdayOfMonth) { if (!nearestWeekday) { t = day; day = GetLastDayOfMonth(mon, d.Year); day -= lastdayOffset; if (t > day) { mon++; if (mon > 12) { mon = 1; tmon = 3333; // 确保下面的 mon != tmon 测试失败 d = d.AddYears(1); } day = 1; } } else { t = day; day = GetLastDayOfMonth(mon, d.Year); day -= lastdayOffset; DateTimeOffset tcal = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); int ldom = GetLastDayOfMonth(mon, d.Year); DayOfWeek dow = tcal.DayOfWeek; if (dow == System.DayOfWeek.Saturday && day == 1) { day += 2; } else if (dow == System.DayOfWeek.Saturday) { day -= 1; } else if (dow == System.DayOfWeek.Sunday && day == ldom) { day -= 2; } else if (dow == System.DayOfWeek.Sunday) { day += 1; } DateTimeOffset nTime = new DateTimeOffset(tcal.Year, mon, day, hr, min, sec, d.Millisecond, d.Offset); if (nTime.ToUniversalTime() < afterTimeUtc) { day = 1; mon++; } } } else if (nearestWeekday) { t = day; day = daysOfMonth.First(); DateTimeOffset tcal = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); int ldom = GetLastDayOfMonth(mon, d.Year); DayOfWeek dow = tcal.DayOfWeek; if (dow == System.DayOfWeek.Saturday && day == 1) { day += 2; } else if (dow == System.DayOfWeek.Saturday) { day -= 1; } else if (dow == System.DayOfWeek.Sunday && day == ldom) { day -= 2; } else if (dow == System.DayOfWeek.Sunday) { day += 1; } tcal = new DateTimeOffset(tcal.Year, mon, day, hr, min, sec, d.Offset); if (tcal.ToUniversalTime() < afterTimeUtc) { day = daysOfMonth.First(); mon++; } } else if (found) { t = day; day = st.First(); //确保我们不会在短时间内跑得过快，比如二月 int lastDay = GetLastDayOfMonth(mon, d.Year); if (day > lastDay) { day = daysOfMonth.First(); mon++; } } else { day = daysOfMonth.First(); mon++; } if (day != t || mon != tmon) { if (mon > 12) { d = new DateTimeOffset(d.Year, 12, day, 0, 0, 0, d.Offset).AddMonths(mon - 12); } else { //这是为了避免从一个月移动时出现错误 //有 30 或 31 天到一个月更少。 导致实例化无效的日期时间。 int lDay = DateTime.DaysInMonth(d.Year, mon); if (day <= lDay) { d = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); } else { d = new DateTimeOffset(d.Year, mon, lDay, 0, 0, 0, d.Offset).AddDays(day - lDay); } } continue; } } else if (dayOfWSpec && !dayOfMSpec) { // 获取星期几规则 if (lastdayOfWeek) { int dow = daysOfWeek.First(); int cDow = (int)d.DayOfWeek + 1; int daysToAdd = 0; if (cDow < dow) { daysToAdd = dow - cDow; } if (cDow > dow) { daysToAdd = dow + (7 - cDow); } int lDay = GetLastDayOfMonth(mon, d.Year); if (day + daysToAdd > lDay) { if (mon == 12) { d = new DateTimeOffset(d.Year, mon - 11, 1, 0, 0, 0, d.Offset).AddYears(1); } else { d = new DateTimeOffset(d.Year, mon + 1, 1, 0, 0, 0, d.Offset); } continue; } // 查找本月这一天最后一次出现的日期... while (day + daysToAdd + 7 <= lDay) { daysToAdd += 7; } day += daysToAdd; if (daysToAdd > 0) { d = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); continue; } } else if (nthdayOfWeek != 0) { int dow = daysOfWeek.First(); int cDow = (int)d.DayOfWeek + 1; int daysToAdd = 0; if (cDow < dow) { daysToAdd = dow - cDow; } else if (cDow > dow) { daysToAdd = dow + (7 - cDow); } bool dayShifted = daysToAdd > 0; day += daysToAdd; int weekOfMonth = day / 7; if (day % 7 > 0) { weekOfMonth++; } daysToAdd = (nthdayOfWeek - weekOfMonth) * 7; day += daysToAdd; if (daysToAdd < 0 || day > GetLastDayOfMonth(mon, d.Year)) { if (mon == 12) { d = new DateTimeOffset(d.Year, mon - 11, 1, 0, 0, 0, d.Offset).AddYears(1); } else { d = new DateTimeOffset(d.Year, mon + 1, 1, 0, 0, 0, d.Offset); } continue; } if (daysToAdd > 0 || dayShifted) { d = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); continue; } } else if (everyNthWeek != 0) { int cDow = (int)d.DayOfWeek + 1; int dow = daysOfWeek.First(); st = daysOfWeek.GetViewBetween(cDow, 9999999); if (st.Count > 0) { dow = st.First(); } int daysToAdd = 0; if (cDow < dow) { daysToAdd = (dow - cDow) + (7 * (everyNthWeek - 1)); } if (cDow > dow) { daysToAdd = (dow + (7 - cDow)) + (7 * (everyNthWeek - 1)); } if (daysToAdd > 0) { d = new DateTimeOffset(d.Year, mon, day, 0, 0, 0, d.Offset); d = d.AddDays(daysToAdd); continue; } } else { int cDow = (int)d.DayOfWeek + 1; int dow = daysOfWeek.First(); st = daysOfWeek.GetViewBetween(cDow, 9999999); if (st.Count > 0) { dow = st.First(); } int daysToAdd = 0; if (cDow < dow) { daysToAdd = dow - cDow; } if (cDow > dow) { daysToAdd = dow + (7 - cDow); } int lDay = GetLastDayOfMonth(mon, d.Year); if (day + daysToAdd > lDay) { if (mon == 12) { d = new DateTimeOffset(d.Year, mon - 11, 1, 0, 0, 0, d.Offset).AddYears(1); } else { d = new DateTimeOffset(d.Year, mon + 1, 1, 0, 0, 0, d.Offset); } continue; } if (daysToAdd > 0) { d = new DateTimeOffset(d.Year, mon, day + daysToAdd, 0, 0, 0, d.Offset); continue; } } } else { throw new FormatException("不支持同时指定星期日和月日参数。"); } d = new DateTimeOffset(d.Year, d.Month, day, d.Hour, d.Minute, d.Second, d.Offset); mon = d.Month; int year = d.Year; t = -1; if (year > MaxYear) { return null; } st = months.GetViewBetween(mon, 9999999); if (st.Count > 0) { t = mon; mon = st.First(); } else { mon = months.First(); year++; } if (mon != t) { d = new DateTimeOffset(year, mon, 1, 0, 0, 0, d.Offset); continue; } d = new DateTimeOffset(d.Year, mon, d.Day, d.Hour, d.Minute, d.Second, d.Offset); year = d.Year; t = -1; st = years.GetViewBetween(year, 9999999); if (st.Count > 0) { t = year; year = st.First(); } else { return null; } if (year != t) { d = new DateTimeOffset(year, 1, 1, 0, 0, 0, d.Offset); continue; } d = new DateTimeOffset(year, d.Month, d.Day, d.Hour, d.Minute, d.Second, d.Offset); //为此日期应用适当的偏移量 d = new DateTimeOffset(d.DateTime, timeZoneInfo.BaseUtcOffset); gotOne = true; } return d.ToUniversalTime(); } /// /// Creates the date time without milliseconds. /// /// The time. /// private static DateTimeOffset CreateDateTimeWithoutMillis(DateTimeOffset time) { return new DateTimeOffset(time.Year, time.Month, time.Day, time.Hour, time.Minute, time.Second, time.Offset); } /// /// Advance the calendar to the particular hour paying particular attention /// to daylight saving problems. /// /// The date. /// The hour. /// private static DateTimeOffset SetCalendarHour(DateTimeOffset date, int hour) { int hourToSet = hour; if (hourToSet == 24) { hourToSet = 0; } DateTimeOffset d = new DateTimeOffset(date.Year, date.Month, date.Day, hourToSet, date.Minute, date.Second, date.Millisecond, date.Offset); if (hour == 24) { d = d.AddDays(1); } return d; } /// /// Gets the last day of month. /// /// The month num. /// The year. /// private static int GetLastDayOfMonth(int monthNum, int year) { return DateTime.DaysInMonth(year, monthNum); } private class ValueSet { public int theValue; public int pos; } } } }
CronHelper 中 CronExpression 的函数计算逻辑是从 Quart.NET 借鉴的，支持标准的 7位 cron 表达式，在需要生成Cron 表达式时可以直接使用网络上的各种 Cron 表达式在线生成
CronHelper 里面我们主要用到的功能就是 通过 Cron 表达式，解析下一次的执行时间。
服务运行这块我们采用微软的 BackgroundService 后台服务，这里还要用到一个后台服务批量注入的逻辑 关于后台逻辑批量注入可以看我之前写的一篇博客，这里就不展开介绍了
.NET 使用自带 DI 批量注入服务（Service）和 后台服务（BackgroundService） https://www.cnblogs.com/berkerdong/p/16496232.html
接下来看一下我这里写的一个DemoTask，代码如下：
using DistributedLock; using Repository.Database; using TaskService.Libraries; namespace TaskService.Tasks { public class DemoTask : BackgroundService { private readonly IServiceProvider serviceProvider; private readonly ILogger logger; public DemoTask(IServiceProvider serviceProvider, ILoggerlogger) { this.serviceProvider = serviceProvider; this.logger = logger; } protected override async Task ExecuteAsync(CancellationToken stoppingToken) { CronSchedule.BatchBuilder(stoppingToken, this); await Task.Delay(-1, stoppingToken); } [CronSchedule(Cron = "0/1 * * * * ?")] public void ClearLog() { try { using var scope = serviceProvider.CreateScope(); var db = scope.ServiceProvider.GetRequiredService (); //省略业务代码 Console.WriteLine("ClearLog:" + DateTime.Now); } catch (Exception ex) { logger.LogError(ex, "DemoTask.ClearLog"); } } [CronSchedule(Cron = "0/5 * * * * ?")] public void ClearCache() { try { using var scope = serviceProvider.CreateScope(); var db = scope.ServiceProvider.GetRequiredService (); var distLock = scope.ServiceProvider.GetRequiredService (); //省略业务代码 Console.WriteLine("ClearCache:" + DateTime.Now); } catch (Exception ex) { logger.LogError(ex, "DemoTask.ClearCache"); } } } }
该Task中有两个方法 ClearLog 和 ClearCache 他们分别会每1秒和每5秒执行一次。需要注意在后台服务中对于 Scope 生命周期的服务在获取是需要手动 CreateScope()；
实现的关键点在于 服务执行 ExecuteAsync 中的 CronSchedule.BatchBuilder(stoppingToken, this); 我们这里将代码有 CronSchedule 标记头的方法全部循环进行了启动，该方法的代码如下：
using Common; using System.Reflection; namespace TaskService.Libraries { public class CronSchedule { public static void BatchBuilder(CancellationToken stoppingToken, object context) { var taskList = context.GetType().GetMethods().Where(t => t.GetCustomAttributes(typeof(CronScheduleAttribute), false).Length > 0).ToList(); foreach (var t in taskList) { string cron = t.CustomAttributes.Where(t => t.AttributeType == typeof(CronScheduleAttribute)).FirstOrDefault()!.NamedArguments.Where(t => t.MemberName == "Cron" && t.TypedValue.Value != null).Select(t => t.TypedValue.Value!.ToString()).FirstOrDefault()!; Builder(stoppingToken, cron, t, context); } } private static async void Builder(CancellationToken stoppingToken, string cronExpression, MethodInfo action, object context) { var nextTime = DateTime.Parse(CronHelper.GetNextOccurrence(cronExpression).ToString("yyyy-MM-dd HH:mm:ss")); while (!stoppingToken.IsCancellationRequested) { var nowTime = DateTime.Parse(DateTimeOffset.UtcNow.ToString("yyyy-MM-dd HH:mm:ss")); if (nextTime == nowTime) { _ = Task.Run(() => { action.Invoke(context, null); }); nextTime = DateTime.Parse(CronHelper.GetNextOccurrence(cronExpression).ToString("yyyy-MM-dd HH:mm:ss")); } else if (nextTime < nowTime) { nextTime = DateTime.Parse(CronHelper.GetNextOccurrence(cronExpression).ToString("yyyy-MM-dd HH:mm:ss")); } await Task.Delay(1000, stoppingToken); } } } [AttributeUsage(AttributeTargets.Method)] public class CronScheduleAttribute : Attribute { public string Cron { get; set; } } }
主要就是利用反射获取当前类中所有带有 CronSchedule 标记的方法，然后解析对应的 Cron 表达式获取下一次的执行时间，如果执行时间等于当前时间则执行一次方法，否则等待1秒钟循环重复这个逻辑。
然后启动我们的项目就可以看到如下的运行效果：
ClearLog 每1秒钟执行一次，ClearCache 每 5秒钟执行一次
至此 .NET 纯原生实现 Cron 定时任务执行，未依赖第三方组件 就讲解完了，有任何不明白的，可以在文章下面评论或者私信我，欢迎大家积极的讨论交流，有兴趣的朋友可以关注我目前在维护的一个 .NET 基础框架项目，项目地址如下