1. 前言
时间包括时间值和时区, 没有包含时区信息的时间是不完整的、有歧义的. 和外界传递或解析时间数据时, 应当像HTTP协议或unix-timestamp那样, 使用没有时区歧义的格式, 如果使用某些没有包含时区的非标准的时间表示格式(如yyyy-mm-dd HH:MM:SS), 是有隐患的, 因为解析时会使用场景的默认设置, 如系统时区, 数据库默认时区可能引发事故. 确保服务器系统、数据库、应用程序使用统一的时区, 如果因为一些历史原因, 应用程序各自保持着不同时区, 那么编程时要小心检查代码, 知道时间数据在使用不同时区的程序之间交换时的行为. 第三节会详细解释go程序在不同场景下time.Time的行为.
2. Time的数据结构
go1.9之前, time.Time的定义为
type Time struct {
// sec gives the number of seconds elapsed since
// January 1, year 1 00:00:00 UTC.
sec int64
// nsec specifies a non-negative nanosecond
// offset within the second named by Seconds.
// It must be in the range [0, 999999999].
nsec int32
// loc specifies the Location that should be used to
// determine the minute, hour, month, day, and year
// that correspond to this Time.
// The nil location means UTC.
// All UTC times are represented with loc==nil, never loc==&utcLoc.
loc *Location
}
sec表示从公元1年1月1日00:00:00UTC到要表示的整数秒数, nsec表示余下的纳秒数, loc表示时区. sec和nsec处理没有歧义的时间值, loc处理偏移量.
因为2017年闰一秒, 国际时钟调整, Go程序两次取time.Now()相减的时间差得到了意料之外的负数, 导致cloudFlare的CDN服务中断, 详见https://blog.cloudflare.com/how-and-why-the-leap-second-affected-cloudflare-dns/, go1.9在不影响已有应用代码的情况下修改了time.Time的实现. go1.9的time.Time定义为
// A Time represents an instant in time with nanosecond precision.
//
// Programs using times should typically store and pass them as values,
// not pointers. That is, time variables and struct fields should be of
// type time.Time, not *time.Time.
//
// A Time value can be used by multiple goroutines simultaneously except
// that the methods GobDecode, UnmarshalBinary, UnmarshalJSON and
// UnmarshalText are not concurrency-safe.
//
// Time instants can be compared using the Before, After, and Equal methods.
// The Sub method subtracts two instants, producing a Duration.
// The Add method adds a Time and a Duration, producing a Time.
//
// The zero value of type Time is January 1, year 1, 00:00:00.000000000 UTC.
// As this time is unlikely to come up in practice, the IsZero method gives
// a simple way of detecting a time that has not been initialized explicitly.
//
// Each Time has associated with it a Location, consulted when computing the
// presentation form of the time, such as in the Format, Hour, and Year methods.
// The methods Local, UTC, and In return a Time with a specific location.
// Changing the location in this way changes only the presentation; it does not
// change the instant in time being denoted and therefore does not affect the
// computations described in earlier paragraphs.
//
// Note that the Go == operator compares not just the time instant but also the
// Location and the monotonic clock reading. Therefore, Time values should not
// be used as map or database keys without first guaranteeing that the
// identical Location has been set for all values, which can be achieved
// through use of the UTC or Local method, and that the monotonic clock reading
// has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u)
// to t == u, since t.Equal uses the most accurate comparison available and
// correctly handles the case when only one of its arguments has a monotonic
// clock reading.
//
// In addition to the required “wall clock” reading, a Time may contain an optional
// reading of the current process's monotonic clock, to provide additional precision
// for comparison or subtraction.
// See the “Monotonic Clocks” section in the package documentation for details.
//
type Time struct {
// wall and ext encode the wall time seconds, wall time nanoseconds,
// and optional monotonic clock reading in nanoseconds.
//
// From high to low bit position, wall encodes a 1-bit flag (hasMonotonic),
// a 33-bit seconds field, and a 30-bit wall time nanoseconds field.
// The nanoseconds field is in the range [0, 999999999].
// If the hasMonotonic bit is 0, then the 33-bit field must be zero
// and the full signed 64-bit wall seconds since Jan 1 year 1 is stored in ext.
// If the hasMonotonic bit is 1, then the 33-bit field holds a 33-bit
// unsigned wall seconds since Jan 1 year 1885, and ext holds a
// signed 64-bit monotonic clock reading, nanoseconds since process start.
wall uint64
ext int64
// loc specifies the Location that should be used to
// determine the minute, hour, month, day, and year
// that correspond to this Time.
// The nil location means UTC.
// All UTC times are represented with loc==nil, never loc==&utcLoc.
loc *Location
}
3. time的行为
func Now() Time {
sec, nsec := now()
return Time{sec + unixToInternal, nsec, Local}
}
func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time {
if loc == nil {
panic("time: missing Location in call to Date")
}
.....
}
// String returns the time formatted using the format string
// "2006-01-02 15:04:05.999999999 -0700 MST"
func (t Time) String() string {
return t.Format("2006-01-02 15:04:05.999999999 -0700 MST")
}
// MarshalJSON implements the json.Marshaler interface.
// The time is a quoted string in RFC 3339 format, with sub-second precision added if present.
func (t Time) MarshalJSON() ([]byte, error) {
if y := t.Year(); y < 0 || y >= 10000 {
// RFC 3339 is clear that years are 4 digits exactly.
// See golang.org/issue/4556#c15 for more discussion.
return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]")
}
b := make([]byte, 0, len(RFC3339Nano)+2)
b = append(b, '"')
b = t.AppendFormat(b, RFC3339Nano)
b = append(b, '"')
return b, nil
}
// UnmarshalJSON implements the json.Unmarshaler interface.
// The time is expected to be a quoted string in RFC 3339 format.
func (t *Time) UnmarshalJSON(data []byte) error {
// Ignore null, like in the main JSON package.
if string(data) == "null" {
return nil
}
// Fractional seconds are handled implicitly by Parse.
var err error
*t, err = Parse(`"`+RFC3339+`"`, string(data))
return err
}
// TimeFormat is the time format to use when generating times in HTTP
// headers. It is like time.RFC1123 but hard-codes GMT as the time
// zone. The time being formatted must be in UTC for Format to
// generate the correct format.
//
// For parsing this time format, see ParseTime.
const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
// Parse parses a formatted string and returns the time value it represents.
// The layout defines the format by showing how the reference time,
// defined to be
// Mon Jan 2 15:04:05 -0700 MST 2006
// would be interpreted if it were the value; it serves as an example of
// the input format. The same interpretation will then be made to the
// input string.
//
// Predefined layouts ANSIC, UnixDate, RFC3339 and others describe standard
// and convenient representations of the reference time. For more information
// about the formats and the definition of the reference time, see the
// documentation for ANSIC and the other constants defined by this package.
// Also, the executable example for time.Format demonstrates the working
// of the layout string in detail and is a good reference.
//
// Elements omitted from the value are assumed to be zero or, when
// zero is impossible, one, so parsing "3:04pm" returns the time
// corresponding to Jan 1, year 0, 15:04:00 UTC (note that because the year is
// 0, this time is before the zero Time).
// Years must be in the range 0000..9999. The day of the week is checked
// for syntax but it is otherwise ignored.
//
// In the absence of a time zone indicator, Parse returns a time in UTC.
//
// When parsing a time with a zone offset like -0700, if the offset corresponds
// to a time zone used by the current location (Local), then Parse uses that
// location and zone in the returned time. Otherwise it records the time as
// being in a fabricated location with time fixed at the given zone offset.
//
// No checking is done that the day of the month is within the month's
// valid dates; any one- or two-digit value is accepted. For example
// February 31 and even February 99 are valid dates, specifying dates
// in March and May. This behavior is consistent with time.Date.
//
// When parsing a time with a zone abbreviation like MST, if the zone abbreviation
// has a defined offset in the current location, then that offset is used.
// The zone abbreviation "UTC" is recognized as UTC regardless of location.
// If the zone abbreviation is unknown, Parse records the time as being
// in a fabricated location with the given zone abbreviation and a zero offset.
// This choice means that such a time can be parsed and reformatted with the
// same layout losslessly, but the exact instant used in the representation will
// differ by the actual zone offset. To avoid such problems, prefer time layouts
// that use a numeric zone offset, or use ParseInLocation.
func Parse(layout, value string) (Time, error) {
return parse(layout, value, UTC, Local)
}
// ParseInLocation is like Parse but differs in two important ways.
// First, in the absence of time zone information, Parse interprets a time as UTC;
// ParseInLocation interprets the time as in the given location.
// Second, when given a zone offset or abbreviation, Parse tries to match it
// against the Local location; ParseInLocation uses the given location.
func ParseInLocation(layout, value string, loc *Location) (Time, error) {
return parse(layout, value, loc, loc)
}
func parse(layout, value string, defaultLocation, local *Location) (Time, error) {
.....
}
4. time时区处理不当案例
var startTime string = time.Now().UTC().Add(8 * time.Hour).Format("2006-01-02")
tm2, _ := time.Parse("2006-01-02", startTime)
lastTime = tm2.Unix() + 24*60*60
// 原版
func GetBjTime() time.Time {
// 将服务器UTC转成北京时间
uTime := time.Now().UTC()
dur, _ := time.ParseDuration("+8h")
return uTime.Add(dur)
}
// 改
func GetBjTime() time.Time {
// 将服务器UTC转成北京时间
uTime := time.Now()
return uTime.In(time.FixedZone("CST", 8*60*60))
}