〇、前言
日常开发过程中，对于时间的操作可谓是无处不在，但是想实现时间自由还是不简单的，多种时间格式容易混淆，那么本文将进行梳理，一起学习下。
官方提供的库是 time，功能很全面，本文也会详细介绍。
还有另外一个开源库 dateparse，使用起来比较方便，本文也会将加入示例测试出结果，以展示其优点。
一、time 库
1.1 Time 类型的结构
go 通过time.Now()来取当前时间，打印出来如下：
2023-09-15 17:59:14.2642387 +0800 CST m=+0.010202701这里存在两个疑点：1）表示秒级的数值为什么默认为 7 位？ 2）最后边的 m=... 代表什么？
1）对于时间戳来说，一般采用秒级或毫秒级。采用浮点数或定点数来表示小数部分，需要一定的字节数来存储，而为了在大多数应用场景下满足足够的精度，一般会选择使用7位数字来表示毫秒级的小数部分，从而达到既满足绝大多数需求又占用尽量上的存储。
2）m 就是 Monotonic Clocks，意思是单调时间的，所谓单调，就是只会不停的往前增长，不受校时操作的影响，这个时间是自进程启动以来的秒数。
在 go1.9 之后，结构更新为：
type Time struct {
wall uint64
ext int64
loc *Location
}Time 结构体中由三部分组成，loc 比较明了，表示时区，wall 和 ext 所存储的信息规则相对复杂，根据文档的介绍总结成了下图：
golang 中的 Time 结构，不像很多语言保存 Unix 时间戳（也就是最早只能表示到 1970 年 1 月 1 日），而是至少可以安全的表示 1885 年以来的时间。
下面来取当前时间测试下：
package main
import (
"encoding/json"
"fmt"
"time"
)
func main() {
now := time.Now() // 取当前时间
time_now := now
fmt.Println(time_now)
for i := 0; i < 5; i++ { // 循环 0~4 共 5 此
time_now = time_now.Add(1 * time.Second) // 每次加 1 秒
fmt.Println(time_now)
}
encodeNow, _ := json.Marshal(now) // 转 json 编码
decodeNow := time.Time{}
json.Unmarshal(encodeNow, &decodeNow) // 将 json 编码转回 Time
fmt.Println(decodeNow)
equal_r := now.Equal(decodeNow)
fmt.Println(equal_r)
}结果如下，可见循环了五次，每次 m 的值都加 1，json 编码转换后的时间中 m 参数消失：
1.2 获取当前时间与格式化
1.2.1 取当前时间
回去当前时间的方法很简单：
now := time.Now()
fmt.Println(now)
// 2023-09-18 13:51:40.8480546 +0800 CST m=+0.008992401
fmt.Println(now.String())
// 2023-09-18 13:51:40.8480546 +0800 CST m=+0.0089924011.2.2 时间格式化
Go 语言提供了时间类型格式化函数 Format()，需要注意的是 Go 语言格式化时间模板不是常见的 Y-m-d H:i:s，而是 2006-01-02 15:04:05，也很好记忆（2006 1 2 3 4 5）。
func (t Time) Format(layout string) string { }time 库中，定义了年、月、日、时、分、秒、周、时区的多种表现形式，如下：
- 年： 06/2006
- 月： 1/01/Jan/January
- 日： 2/02/_2
- 时： 3/03/15/PM/pm/AM/am
- 分： 4/04
- 秒： 5/05
- 周： Mon/Monday
- 时区：-07/-0700/Z0700/Z07:00/-07:00/MST
这些格式的形式配置，可以根据自己的需求自由组合，一下是部分组合的测试：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now)
fmt.Println("2006-01-02 15:04:05 output:", now.Format("2006-01-02 15:04:05"))
fmt.Println("2006-01-02 output:", now.Format("2006-01-02"))
fmt.Println("01-02-2006 output:", now.Format("01-02-2006"))
fmt.Println("15:03:04 output:", now.Format("15:03:04"))
fmt.Println("2006/01/02 15:04 output:", now.Format("2006/01/02 15:04"))
fmt.Println("15:04 2006/01/02 output:", now.Format("15:04 2006/01/02"))
fmt.Println("2006#01#02 output:", now.Format("2006#01#02"))
fmt.Println("2006$01$02 output:", now.Format("2006$01$02"))
fmt.Println("2006-01-02 15:04:05.000 output:", now.Format("2006-01-02 15:04:05.000"))
fmt.Println("2006-01-02 15:04:05.000000000 output:", now.Format("2006-01-02 15:04:05.000000000"))
fmt.Println("2006-January-02 15:04:05 Monday output:", now.Format("2006-January-02 15:04:05 Monday"))
fmt.Println("2006-Jan-02 15:04:05 Mon output:", now.Format("2006-Jan-02 15:04:05 Mon"))
fmt.Println("2006-1-2 3:4:5 PM output:", now.Format("2006-1-2 3:4:5 PM"))
}
字符串类型的日期转 Time：
package main
import (
"fmt"
"time"
)
func main() {
t, _ := time.ParseInLocation("2006-01-02", "2023-09-18", time.Local) // time.Local 指定本地时间
fmt.Println(t)
t, _ = time.ParseInLocation("2006-01-02 15:04:05", "2023-09-18 17:46:13", time.Local)
fmt.Println(t)
t, _ = time.ParseInLocation("2006-01-02 15:04:05", "2023-09-18", time.Local)
fmt.Println(t) // 当时间字符串和标准字符串不统一时，转化失败
}
1.2.3 取日期的单个值
日期的组成部分比较多，下面来尝试取出各个部分的值：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
// 返回日期
year, month, day := now.Date()
fmt.Printf("日期：%d年%d月%d日\n", year, month, day)
fmt.Println("年：", now.Year()) // int
fmt.Println("月：", now.Month()) // time.Month
fmt.Println("月：", now.Month().String())
fmt.Println("月：", int(now.Month()))
fmt.Println("日：", now.Day()) // int
// 时分秒
hour, minute, second := now.Clock()
fmt.Printf("时间：%d:%d:%d\n", hour, minute, second)
fmt.Println("时：", now.Hour()) // int
fmt.Println("分：", now.Minute()) // int
fmt.Println("秒：", now.Second()) // int
fmt.Println("星期：", now.Weekday()) // time.Weekday
fmt.Println("星期：", now.Weekday().String()) // 不能得到 一、二。。。
fmt.Println("星期：", int(now.Weekday())) // 可以通过取得的 1、2。。。来计算是周几
fmt.Println("天数：", now.YearDay()) // int
fmt.Println("时区：", now.Location())
}
1.3 日期的计算
计算之前或之后一段时间：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now, "（当前时间）")
// func (t Time) AddDate(years int, months int, days int) Time
m0 := now.AddDate(1, 1, 1)
fmt.Println(m0, "（now.AddDate(1,1,1)）")
m00 := now.AddDate(0, 1, 1)
fmt.Println(m00, "（now.AddDate(0,1,1)）")
// func ParseDuration(s string) (Duration, error)
// s string："ns", "us" (or "µs"), "ms", "s", "m", "h"
t1, _ := time.ParseDuration("1h1m1s") // 亦可：48h1m1s
m1 := now.Add(t1)
fmt.Println(m1, "（1小时1分1s之后）")
t2, _ := time.ParseDuration("-1h1m1s")
m2 := now.Add(t2)
fmt.Println(m2, "（1小时1分1s之前）")
t3, _ := time.ParseDuration("-1h")
m3 := now.Add(t3 * 3)
fmt.Println(m3, "（3小时之前）")
}
时间差和比较时间大小：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now, "（当前时间）")
// func (t Time) Sub(u Time) Duration // 取时间差对象
sub1 := now.Sub(m1)
fmt.Println(sub1.Hours(), "（相差小时数）")
fmt.Println(sub1.Minutes(), "（相差分钟数）")
// time.Since(t Time) Duration // 返回当前时间与 t 的时间差，返回值是 Duration
// time.Until(t Time) Duration // 返回 t 与当前时间的时间差，返回值是 Duration
t1s, _ := time.ParseDuration("-1h")
m1s := now.Add(t1s)
fmt.Println(time.Since(m1s), "（Since）")
fmt.Println(time.Until(m1s), "（Until）")
// func (t Time) Before(u Time) bool // 如果 t 代表的时间点在 u 之前，返回真；否则返回假
// func (t Time) After(u Time) bool // 如果 t 代表的时间点在 u 之后，返回真；否则返回假
// func (t Time) Equal(u Time) bool // 比较时间是否相等，相等返回真；否则返回假
t1m, _ := time.ParseDuration("1h")
m1m := now.Add(t1m)
fmt.Println(m1m)
fmt.Println(m1m.After(now), "（After(now)）")
fmt.Println(m1m.Before(now), "（Before(now)）")
fmt.Println(now.Equal(m1m), "（Equal(m1m)）")
}
1.4 时间戳
如何取时间戳：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now, "（当前时间）")
// 取时间戳
fmt.Println(now.Unix()) // 当前时间戳
fmt.Println(now.UnixMilli()) // 毫秒级时间戳
fmt.Println(now.UnixMicro()) // 微秒级时间戳
fmt.Println(now.UnixNano()) // 纳秒级时间戳
fmt.Println(now.Nanosecond()) // 时间戳小数部分 单位：纳秒
}
时间戳与时间的简单转换：
package main
import (
"fmt"
"time"
)
func main() {
now := time.Now()
fmt.Println(now, "（当前时间）")
unix := now.Unix()
fmt.Println(unix, "（秒级时间戳）")
t := time.Unix(unix, 0)
fmt.Println(t, "（原时间）")
t = time.Unix(unix, 1) // 在时间戳的基础上，加 1 纳秒
fmt.Println(t, "（加 1 纳秒）")
micro_unix := now.UnixMicro()
fmt.Println(micro_unix, "（微秒级时间戳）")
t1 := time.UnixMicro(micro_unix)
fmt.Println(t1)
}
参考：https://zhuanlan.zhihu.com/p/362936088 https://zhuanlan.zhihu.com/p/145009400 https://zhuanlan.zhihu.com/p/47754783
二、dateparse 库
dateparse 库的作用主要就是将不同格式的字符串类型的时间，转为 Time 时间类型。源码地址：https://github.com/araddon/dateparse
根据本文 1.2.2 章节中第二部分 的转换方法，并不能用于全部字符串日期的转换，容易出现转换失败的情况。另外需要根据源日期的格式组织标准日期的格式，也会增加工作量。但是，当用上 dateparse 库后，这一切将变的非常简单。
dateparse 库，就是将各种类型的日期格式字符串，转换成同样的格式，参考：2006-01-02 15:04:05 +0000 UTC。
具体引用的方法是func ParseLocal(datestr string, opts ...ParserOption) (time.Time, error){ }，调用示例为Time_date_output := dateparse.ParseLocal(str_date_input)。
以下代码是 github 上源码中的示例，供参考：
package main
import (
"flag"
"fmt"
"time"
"github.com/scylladb/termtables"
"github.com/araddon/dateparse"
)
var examples = []string{
"May 8, 2009 5:57:51 PM",
"oct 7, 1970",
"oct 7, '70",
...
}
var (
timezone = ""
)
func main() {
flag.StringVar(&timezone, "timezone", "UTC", "Timezone aka `America/Los_Angeles` formatted time-zone")
flag.Parse() // 取命令行参数 timezone
if timezone != "" {
loc, err := time.LoadLocation(timezone)
if err != nil {
panic(err.Error())
}
time.Local = loc // 将默认的本地值修改为输入的本地参数
}
table := termtables.CreateTable()
table.AddHeaders("Input", "Parsed, and Output as %v")
for _, dateExample := range examples { // 循环全部日期格式字符串，并输出转换后的格式
t, err := dateparse.ParseLocal(dateExample)
if err != nil {
panic(err.Error())
}
table.AddRow(dateExample, fmt.Sprintf("%v", t))
}
fmt.Println(table.Render())
}
/*
+-------------------------------------------------------+-----------------------------------------+
| Input | Parsed, and Output as %v |
+-------------------------------------------------------+-----------------------------------------+
| May 8, 2009 5:57:51 PM | 2009-05-08 17:57:51 +0000 UTC |
| oct 7, 1970 | 1970-10-07 00:00:00 +0000 UTC |
| oct 7, '70 | 1970-10-07 00:00:00 +0000 UTC |
| oct. 7, 1970 | 1970-10-07 00:00:00 +0000 UTC |
| oct. 7, 70 | 1970-10-07 00:00:00 +0000 UTC |
| Mon Jan 2 15:04:05 2006 | 2006-01-02 15:04:05 +0000 UTC |
| Mon Jan 2 15:04:05 MST 2006 | 2006-01-02 15:04:05 +0000 MST |
| Mon Jan 02 15:04:05 -0700 2006 | 2006-01-02 15:04:05 -0700 -0700 |
| Monday, 02-Jan-06 15:04:05 MST | 2006-01-02 15:04:05 +0000 MST |
| Mon, 02 Jan 2006 15:04:05 MST | 2006-01-02 15:04:05 +0000 MST |
| Tue, 11 Jul 2017 16:28:13 +0200 (CEST) | 2017-07-11 16:28:13 +0200 +0200 |
| Mon, 02 Jan 2006 15:04:05 -0700 | 2006-01-02 15:04:05 -0700 -0700 |
| Mon 30 Sep 2018 09:09:09 PM UTC | 2018-09-30 21:09:09 +0000 UTC |
| Mon Aug 10 15:44:11 UTC+0100 2015 | 2015-08-10 15:44:11 +0000 UTC |
| Thu, 4 Jan 2018 17:53:36 +0000 | 2018-01-04 17:53:36 +0000 UTC |
| Fri Jul 03 2015 18:04:07 GMT+0100 (GMT Daylight Time) | 2015-07-03 18:04:07 +0100 GMT |
| Sun, 3 Jan 2021 00:12:23 +0800 (GMT+08:00) | 2021-01-03 00:12:23 +0800 +0800 |
| September 17, 2012 10:09am | 2012-09-17 10:09:00 +0000 UTC |
| September 17, 2012 at 10:09am PST-08 | 2012-09-17 10:09:00 -0800 PST |
| September 17, 2012, 10:10:09 | 2012-09-17 10:10:09 +0000 UTC |
| October 7, 1970 | 1970-10-07 00:00:00 +0000 UTC |
| October 7th, 1970 | 1970-10-07 00:00:00 +0000 UTC |
| 12 Feb 2006, 19:17 | 2006-02-12 19:17:00 +0000 UTC |
| 12 Feb 2006 19:17 | 2006-02-12 19:17:00 +0000 UTC |
| 14 May 2019 19:11:40.164 | 2019-05-14 19:11:40.164 +0000 UTC |
| 7 oct 70 | 1970-10-07 00:00:00 +0000 UTC |
| 7 oct 1970 | 1970-10-07 00:00:00 +0000 UTC |
| 03 February 2013 | 2013-02-03 00:00:00 +0000 UTC |
| 1 July 2013 | 2013-07-01 00:00:00 +0000 UTC |
| 2013-Feb-03 | 2013-02-03 00:00:00 +0000 UTC |
| 06/Jan/2008:15:04:05 -0700 | 2008-01-06 15:04:05 -0700 -0700 |
| 06/Jan/2008 15:04:05 -0700 | 2008-01-06 15:04:05 -0700 -0700 |
| 3/31/2014 | 2014-03-31 00:00:00 +0000 UTC |
| 03/31/2014 | 2014-03-31 00:00:00 +0000 UTC |
| 08/21/71 | 1971-08-21 00:00:00 +0000 UTC |
| 8/1/71 | 1971-08-01 00:00:00 +0000 UTC |
| 4/8/2014 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 04/08/2014 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 4/8/14 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 04/2/2014 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 8/8/1965 12:00:00 AM | 1965-08-08 00:00:00 +0000 UTC |
| 8/8/1965 01:00:01 PM | 1965-08-08 13:00:01 +0000 UTC |
| 8/8/1965 01:00 PM | 1965-08-08 13:00:00 +0000 UTC |
| 8/8/1965 1:00 PM | 1965-08-08 13:00:00 +0000 UTC |
| 8/8/1965 12:00 AM | 1965-08-08 00:00:00 +0000 UTC |
| 4/02/2014 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 03/19/2012 10:11:59 | 2012-03-19 10:11:59 +0000 UTC |
| 03/19/2012 10:11:59.3186369 | 2012-03-19 10:11:59.3186369 +0000 UTC |
| 2014/3/31 | 2014-03-31 00:00:00 +0000 UTC |
| 2014/03/31 | 2014-03-31 00:00:00 +0000 UTC |
| 2014/4/8 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 2014/04/08 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 2014/04/2 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 2014/4/02 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 2012/03/19 10:11:59 | 2012-03-19 10:11:59 +0000 UTC |
| 2012/03/19 10:11:59.3186369 | 2012-03-19 10:11:59.3186369 +0000 UTC |
| 2014:3:31 | 2014-03-31 00:00:00 +0000 UTC |
| 2014:03:31 | 2014-03-31 00:00:00 +0000 UTC |
| 2014:4:8 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 2014:04:08 22:05 | 2014-04-08 22:05:00 +0000 UTC |
| 2014:04:2 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 2014:4:02 03:00:51 | 2014-04-02 03:00:51 +0000 UTC |
| 2012:03:19 10:11:59 | 2012-03-19 10:11:59 +0000 UTC |
| 2012:03:19 10:11:59.3186369 | 2012-03-19 10:11:59.3186369 +0000 UTC |
| 2014年04月08日 | 2014-04-08 00:00:00 +0000 UTC |
| 2006-01-02T15:04:05+0000 | 2006-01-02 15:04:05 +0000 UTC |
| 2009-08-12T22:15:09-07:00 | 2009-08-12 22:15:09 -0700 -0700 |
| 2009-08-12T22:15:09 | 2009-08-12 22:15:09 +0000 UTC |
| 2009-08-12T22:15:09.988 | 2009-08-12 22:15:09.988 +0000 UTC |
| 2009-08-12T22:15:09Z | 2009-08-12 22:15:09 +0000 UTC |
| 2017-07-19T03:21:51:897+0100 | 2017-07-19 03:21:51.897 +0100 +0100 |
| 2019-05-29T08:41-04 | 2019-05-29 08:41:00 -0400 -0400 |
| 2014-04-26 17:24:37.3186369 | 2014-04-26 17:24:37.3186369 +0000 UTC |
| 2012-08-03 18:31:59.257000000 | 2012-08-03 18:31:59.257 +0000 UTC |
| 2014-04-26 17:24:37.123 | 2014-04-26 17:24:37.123 +0000 UTC |
| 2013-04-01 22:43 | 2013-04-01 22:43:00 +0000 UTC |
| 2013-04-01 22:43:22 | 2013-04-01 22:43:22 +0000 UTC |
| 2014-12-16 06:20:00 UTC | 2014-12-16 06:20:00 +0000 UTC |
| 2014-12-16 06:20:00 GMT | 2014-12-16 06:20:00 +0000 UTC |
| 2014-04-26 05:24:37 PM | 2014-04-26 17:24:37 +0000 UTC |
| 2014-04-26 13:13:43 +0800 | 2014-04-26 13:13:43 +0800 +0800 |
| 2014-04-26 13:13:43 +0800 +08 | 2014-04-26 13:13:43 +0800 +0800 |
| 2014-04-26 13:13:44 +09:00 | 2014-04-26 13:13:44 +0900 +0900 |
| 2012-08-03 18:31:59.257000000 +0000 UTC | 2012-08-03 18:31:59.257 +0000 UTC |
| 2015-09-30 18:48:56.35272715 +0000 UTC | 2015-09-30 18:48:56.35272715 +0000 UTC |
| 2015-02-18 00:12:00 +0000 GMT | 2015-02-18 00:12:00 +0000 UTC |
| 2015-02-18 00:12:00 +0000 UTC | 2015-02-18 00:12:00 +0000 UTC |
| 2015-02-08 03:02:00 +0300 MSK m=+0.000000001 | 2015-02-08 03:02:00 +0300 +0300 |
| 2015-02-08 03:02:00.001 +0300 MSK m=+0.000000001 | 2015-02-08 03:02:00.001 +0300 +0300 |
| 2017-07-19 03:21:51+00:00 | 2017-07-19 03:21:51 +0000 UTC |
| 2014-04-26 | 2014-04-26 00:00:00 +0000 UTC |
| 2014-04 | 2014-04-01 00:00:00 +0000 UTC |
| 2014 | 2014-01-01 00:00:00 +0000 UTC |
| 2014-05-11 08:20:13,787 | 2014-05-11 08:20:13.787 +0000 UTC |
| 2020-07-20+08:00 | 2020-07-20 00:00:00 +0800 +0800 |
| 3.31.2014 | 2014-03-31 00:00:00 +0000 UTC |
| 03.31.2014 | 2014-03-31 00:00:00 +0000 UTC |
| 08.21.71 | 1971-08-21 00:00:00 +0000 UTC |
| 2014.03 | 2014-03-01 00:00:00 +0000 UTC |
| 2014.03.30 | 2014-03-30 00:00:00 +0000 UTC |
| 20140601 | 2014-06-01 00:00:00 +0000 UTC |
| 20140722105203 | 2014-07-22 10:52:03 +0000 UTC |
| 171113 14:14:20 | 2017-11-13 14:14:20 +0000 UTC |
| 1332151919 | 2012-03-19 10:11:59 +0000 UTC |
| 1384216367189 | 2013-11-12 00:32:47.189 +0000 UTC |
| 1384216367111222 | 2013-11-12 00:32:47.111222 +0000 UTC |
| 1384216367111222333 | 2013-11-12 00:32:47.111222333 +0000 UTC |
+-------------------------------------------------------+-----------------------------------------+
*/