golang的时区和神奇的time.Parse

时区


先写一段测试代码:

const TIME_LAYOUT = "2006-01-02 15:04:05"

func parseWithLocation(name string, timeStr string) (time.Time, error) {
    locationName := name
    if l, err := time.LoadLocation(locationName); err != nil {
        println(err.Error())
        return time.Time{}, err
    } else {
        lt, _ := time.ParseInLocation(TIME_LAYOUT, timeStr, l)
        fmt.Println(locationName, lt)
        return lt, nil
    }
}
func testTime() {
    fmt.Println("0. now: ", time.Now())
    str := "2018-09-10 00:00:00"
    fmt.Println("1. str: ", str)
    t, _ := time.Parse(TIME_LAYOUT, str)
    fmt.Println("2. Parse time: ", t)
    tStr := t.Format(TIME_LAYOUT)
    fmt.Println("3. Format time str: ", tStr)
    name, offset := t.Zone()
    name2, offset2 := t.Local().Zone()
    fmt.Printf("4. Zone name: %v, Zone offset: %v\n", name, offset)
    fmt.Printf("5. Local Zone name: %v, Local Zone offset: %v\n", name2, offset2)
    tLocal := t.Local()
    tUTC := t.UTC()
    fmt.Printf("6. t: %v, Local: %v, UTC: %v\n", t, tLocal, tUTC)
    fmt.Printf("7. t: %v, Local: %v, UTC: %v\n", t.Format(TIME_LAYOUT), tLocal.Format(TIME_LAYOUT), tUTC.Format(TIME_LAYOUT))
    fmt.Printf("8. Local.Unix: %v, UTC.Unix: %v\n", tLocal.Unix(), tUTC.Unix())
    str2 := "1969-12-31 23:59:59"
    t2, _ := time.Parse(TIME_LAYOUT, str2)
    fmt.Printf("9. str2:%v,time: %v, Unix: %v\n", str2, t2, t2.Unix())
    fmt.Printf("10. %v, %v\n", tLocal.Format(time.ANSIC), tUTC.Format(time.ANSIC))
    fmt.Printf("11. %v, %v\n", tLocal.Format(time.RFC822), tUTC.Format(time.RFC822))
    fmt.Printf("12. %v, %v\n", tLocal.Format(time.RFC822Z), tUTC.Format(time.RFC822Z))

    //指定时区
    parseWithLocation("America/Cordoba", str)
    parseWithLocation("Asia/Shanghai", str)
    parseWithLocation("Asia/Beijing", str)
}
testTime()

输出:

0. now:  2018-09-19 19:06:07.3642781 +0800 CST m=+0.005995601
1. str:  2018-09-10 00:00:00
2. Parse time:  2018-09-10 00:00:00 +0000 UTC
3. Format time str:  2018-09-10 00:00:00
4. Zone name: UTC, Zone offset: 0
5. Local Zone name: CST, Local Zone offset: 28800
6. t: 2018-09-10 00:00:00 +0000 UTC, Local: 2018-09-10 08:00:00 +0800 CST, UTC: 2018-09-10 00:00:00 +0000 UTC
7. t: 2018-09-10 00:00:00, Local: 2018-09-10 08:00:00, UTC: 2018-09-10 00:00:00
8. Local.Unix: 1536537600, UTC.Unix: 1536537600
9. str2:1969-12-31 23:59:59,time: 1969-12-31 23:59:59 +0000 UTC, Unix: -1
10. Mon Sep 10 08:00:00 2018, Mon Sep 10 00:00:00 2018
11. 10 Sep 18 08:00 CST, 10 Sep 18 00:00 UTC
12. 10 Sep 18 08:00 +0800, 10 Sep 18 00:00 +0000
America/Cordoba 2018-09-10 00:00:00 -0300 -03
Asia/Shanghai 2018-09-10 00:00:00 +0800 CST
cannot find Asia/Beijing in zip file C:\Go\/lib/time/zoneinfo.zip

从以上代码的测试结果可以得出几点:

  1. time.Now 得到的当前时间的时区跟电脑的当前时区一样。
  2. time.Parse 把时间字符串转换为Time,时区是UTC时区。
  3. 不管Time变量存储的是什么时区,其Unix()方法返回的都是距离UTC时间:1970年1月1日0点0分0秒的秒数。
  4. Unix()返回的秒数可以是负数,如果时间小于1970-01-01 00:00:00的话。
  5. Zone方法可以获得变量的时区和时区与UTC的偏移秒数,应该支持夏令时和冬令时。
  6. time.LoadLocation可以根据时区名创建时区Location,所有的时区名字可以在$GOROOT/lib/time/zoneinfo.zip文件中找到,解压zoneinfo.zip可以得到一堆目录和文件,我们只需要目录和文件的名字,时区名是目录名+文件名,比如"Asia/Shanghai"。中国时区名只有"Asia/Shanghai""Asia/Chongqing",而没有"Asia/Beijing"
  7. time.ParseInLocation可以根据时间字符串和指定时区转换Time。
  8. 感谢中国只有一个时区而且没有夏令时和冬令时,可怕的美国居然有6个时区,想想都可怕。

神奇的time.Parse


一开始使用time.Parse时很不习惯,因为非常奇怪的layout参数。
除了golang自带定义的layout

const (
    ANSIC       = "Mon Jan _2 15:04:05 2006"
    UnixDate    = "Mon Jan _2 15:04:05 MST 2006"
    RubyDate    = "Mon Jan 02 15:04:05 -0700 2006"
    RFC822      = "02 Jan 06 15:04 MST"
    RFC822Z     = "02 Jan 06 15:04 -0700" // RFC822 with numeric zone
    RFC850      = "Monday, 02-Jan-06 15:04:05 MST"
    RFC1123     = "Mon, 02 Jan 2006 15:04:05 MST"
    RFC1123Z    = "Mon, 02 Jan 2006 15:04:05 -0700" // RFC1123 with numeric zone
    RFC3339     = "2006-01-02T15:04:05Z07:00"
    RFC3339Nano = "2006-01-02T15:04:05.999999999Z07:00"
    Kitchen     = "3:04PM"
    // Handy time stamps.
    Stamp      = "Jan _2 15:04:05"
    StampMilli = "Jan _2 15:04:05.000"
    StampMicro = "Jan _2 15:04:05.000000"
    StampNano  = "Jan _2 15:04:05.000000000"
)

还可以自定义layout,比如:

"2006-01-02 15:04:05"

网上基本上都在传说这个日子是golang项目开始创建的时间,为了纪念生日才这样设计,其实这真是无稽之谈瞎扯淡。
网上文章没有找到说的比较清楚的,幸好有源码,打开time.Parse的源码看了一下,发现这个设计很好很科学。
解析layout的主要代码在nextStdChunk方法中:

// nextStdChunk finds the first occurrence of a std string in
// layout and returns the text before, the std string, and the text after.
func nextStdChunk(layout string) (prefix string, std int, suffix string) {
    for i := 0; i < len(layout); i++ {
        switch c := int(layout[i]); c {
        case 'J': // January, Jan
            if len(layout) >= i+3 && layout[i:i+3] == "Jan" {
                if len(layout) >= i+7 && layout[i:i+7] == "January" {
                    return layout[0:i], stdLongMonth, layout[i+7:]
                }
                if !startsWithLowerCase(layout[i+3:]) {
                    return layout[0:i], stdMonth, layout[i+3:]
                }
            }

        case 'M': // Monday, Mon, MST
            if len(layout) >= i+3 {
                if layout[i:i+3] == "Mon" {
                    if len(layout) >= i+6 && layout[i:i+6] == "Monday" {
                        return layout[0:i], stdLongWeekDay, layout[i+6:]
                    }
                    if !startsWithLowerCase(layout[i+3:]) {
                        return layout[0:i], stdWeekDay, layout[i+3:]
                    }
                }
                if layout[i:i+3] == "MST" {
                    return layout[0:i], stdTZ, layout[i+3:]
                }
            }

        case '0': // 01, 02, 03, 04, 05, 06
            if len(layout) >= i+2 && '1' <= layout[i+1] && layout[i+1] <= '6' {
                return layout[0:i], std0x[layout[i+1]-'1'], layout[i+2:]
            }

        case '1': // 15, 1
            if len(layout) >= i+2 && layout[i+1] == '5' {
                return layout[0:i], stdHour, layout[i+2:]
            }
            return layout[0:i], stdNumMonth, layout[i+1:]

        case '2': // 2006, 2
            if len(layout) >= i+4 && layout[i:i+4] == "2006" {
                return layout[0:i], stdLongYear, layout[i+4:]
            }
            return layout[0:i], stdDay, layout[i+1:]

        case '_': // _2, _2006
            if len(layout) >= i+2 && layout[i+1] == '2' {
                //_2006 is really a literal _, followed by stdLongYear
                if len(layout) >= i+5 && layout[i+1:i+5] == "2006" {
                    return layout[0 : i+1], stdLongYear, layout[i+5:]
                }
                return layout[0:i], stdUnderDay, layout[i+2:]
            }

        case '3':
            return layout[0:i], stdHour12, layout[i+1:]

        case '4':
            return layout[0:i], stdMinute, layout[i+1:]

        case '5':
            return layout[0:i], stdSecond, layout[i+1:]

        case 'P': // PM
            if len(layout) >= i+2 && layout[i+1] == 'M' {
                return layout[0:i], stdPM, layout[i+2:]
            }

        case 'p': // pm
            if len(layout) >= i+2 && layout[i+1] == 'm' {
                return layout[0:i], stdpm, layout[i+2:]
            }

        case '-': // -070000, -07:00:00, -0700, -07:00, -07
            if len(layout) >= i+7 && layout[i:i+7] == "-070000" {
                return layout[0:i], stdNumSecondsTz, layout[i+7:]
            }
            if len(layout) >= i+9 && layout[i:i+9] == "-07:00:00" {
                return layout[0:i], stdNumColonSecondsTZ, layout[i+9:]
            }
            if len(layout) >= i+5 && layout[i:i+5] == "-0700" {
                return layout[0:i], stdNumTZ, layout[i+5:]
            }
            if len(layout) >= i+6 && layout[i:i+6] == "-07:00" {
                return layout[0:i], stdNumColonTZ, layout[i+6:]
            }
            if len(layout) >= i+3 && layout[i:i+3] == "-07" {
                return layout[0:i], stdNumShortTZ, layout[i+3:]
            }

        case 'Z': // Z070000, Z07:00:00, Z0700, Z07:00,
            if len(layout) >= i+7 && layout[i:i+7] == "Z070000" {
                return layout[0:i], stdISO8601SecondsTZ, layout[i+7:]
            }
            if len(layout) >= i+9 && layout[i:i+9] == "Z07:00:00" {
                return layout[0:i], stdISO8601ColonSecondsTZ, layout[i+9:]
            }
            if len(layout) >= i+5 && layout[i:i+5] == "Z0700" {
                return layout[0:i], stdISO8601TZ, layout[i+5:]
            }
            if len(layout) >= i+6 && layout[i:i+6] == "Z07:00" {
                return layout[0:i], stdISO8601ColonTZ, layout[i+6:]
            }
            if len(layout) >= i+3 && layout[i:i+3] == "Z07" {
                return layout[0:i], stdISO8601ShortTZ, layout[i+3:]
            }

        case '.': // .000 or .999 - repeated digits for fractional seconds.
            if i+1 < len(layout) && (layout[i+1] == '0' || layout[i+1] == '9') {
                ch := layout[i+1]
                j := i + 1
                for j < len(layout) && layout[j] == ch {
                    j++
                }
                // String of digits must end here - only fractional second is all digits.
                if !isDigit(layout, j) {
                    std := stdFracSecond0
                    if layout[i+1] == '9' {
                        std = stdFracSecond9
                    }
                    std |= (j - (i + 1)) << stdArgShift
                    return layout[0:i], std, layout[j:]
                }
            }
        }
    }
    return layout, 0, ""
}

可以发现layout的所有代表年月日时分秒甚至时区的值都是互斥不相等的。

比如年份:短年份06,长年份2006,
月份:01,Jan,January
日:02,2,_2
时:15,3,03
分:04, 4
秒:05, 5

因为都不相等所以通过遍历layout就可以switch case解析出每个区块的意义和在字符串中的位置,这样输入对应格式的时间字符串就可以顺利解析出来。
这样layout也可以自定义,而且顺序任意,只要符合下列每个区块定义的规则即可,
代码中的注释就是规则写法:

const (
    _                        = iota
    stdLongMonth             = iota + stdNeedDate  // "January"
    stdMonth                                       // "Jan"
    stdNumMonth                                    // "1"
    stdZeroMonth                                   // "01"
    stdLongWeekDay                                 // "Monday"
    stdWeekDay                                     // "Mon"
    stdDay                                         // "2"
    stdUnderDay                                    // "_2"
    stdZeroDay                                     // "02"
    stdHour                  = iota + stdNeedClock // "15"
    stdHour12                                      // "3"
    stdZeroHour12                                  // "03"
    stdMinute                                      // "4"
    stdZeroMinute                                  // "04"
    stdSecond                                      // "5"
    stdZeroSecond                                  // "05"
    stdLongYear              = iota + stdNeedDate  // "2006"
    stdYear                                        // "06"
    stdPM                    = iota + stdNeedClock // "PM"
    stdpm                                          // "pm"
    stdTZ                    = iota                // "MST"
    stdISO8601TZ                                   // "Z0700"  // prints Z for UTC
    stdISO8601SecondsTZ                            // "Z070000"
    stdISO8601ShortTZ                              // "Z07"
    stdISO8601ColonTZ                              // "Z07:00" // prints Z for UTC
    stdISO8601ColonSecondsTZ                       // "Z07:00:00"
    stdNumTZ                                       // "-0700"  // always numeric
    stdNumSecondsTz                                // "-070000"
    stdNumShortTZ                                  // "-07"    // always numeric
    stdNumColonTZ                                  // "-07:00" // always numeric
    stdNumColonSecondsTZ                           // "-07:00:00"
    stdFracSecond0                                 // ".0", ".00", ... , trailing zeros included
    stdFracSecond9                                 // ".9", ".99", ..., trailing zeros omitted

    stdNeedDate  = 1 << 8             // need month, day, year
    stdNeedClock = 2 << 8             // need hour, minute, second
    stdArgShift  = 16                 // extra argument in high bits, above low stdArgShift
    stdMask      = 1<<stdArgShift - 1 // mask out argument
)

时区:
时区使用:MST
时区偏移使用-0700或者Z0700等等。
下面是一个使用时区的例子,Z0700比较特殊,当输入时间直接使用Z时就直接代表UTC时区。

func testTimeParse() {
    t, _ := time.Parse("2006-01-02 15:04:05 -0700 MST", "2018-09-20 15:39:06 +0800 CST")
    fmt.Println(t)
    t, _ = time.Parse("2006-01-02 15:04:05 -0700 MST", "2018-09-20 15:39:06 +0000 CST")
    fmt.Println(t)
    t, _ = time.Parse("2006-01-02 15:04:05 Z0700 MST", "2018-09-20 15:39:06 +0800 CST")
    fmt.Println(t)
    t, _ = time.Parse("2006-01-02 15:04:05 Z0700 MST", "2018-09-20 15:39:06 Z GMT")
    fmt.Println(t)
    t, _ = time.Parse("2006-01-02 15:04:05 Z0700 MST", "2018-09-20 15:39:06 +0000 GMT")
    fmt.Println(t)
}
输出:
2018-09-20 15:39:06 +0800 CST
2018-09-20 15:39:06 +0000 CST
2018-09-20 15:39:06 +0800 CST
2018-09-20 15:39:06 +0000 UTC
2018-09-20 15:39:06 +0000 GMT

还有疑问的可以看看go自带的测试例子:
Go/src/time/example_test.go

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