Override the layout used by json.Marshal to format time.Time
Solution 1
As inspired by zeebo's answer and hashed out in the comments to that answer:
http://play.golang.org/p/pUCBUgrjZC
package main
import "fmt"
import "time"
import "encoding/json"
type jsonTime struct {
time.Time
f string
}
func (j jsonTime) format() string {
return j.Time.Format(j.f)
}
func (j jsonTime) MarshalText() ([]byte, error) {
return []byte(j.format()), nil
}
func (j jsonTime) MarshalJSON() ([]byte, error) {
return []byte(`"` + j.format() + `"`), nil
}
func main() {
jt := jsonTime{time.Now(), time.Kitchen}
if jt.Before(time.Now().AddDate(0, 0, 1)) { // 1
x := map[string]interface{}{
"foo": jt,
"bar": "baz",
}
data, err := json.Marshal(x)
if err != nil {
panic(err)
}
fmt.Printf("%s", data)
}
}
This solution embeds the time.Time into the jsonTime struct. Embedding promotes all of time.Time's methods to the jsonTime struct, allowing their use without explicit type conversion (see // 1).
Embedding a time.Time has the downside of also promoting the MarshalJSON method, which the encoding/json marshaling code prioritizes higher than the MarshalText method for backwards compatibility reasons (MarshalText was added in Go 1.2, MarshalJSON predates that). As a result the default time.Time format is used instead of a custom format provided by MarshalText.
To overcome this problem we override MarshalJSON for the jsonTime struct.
Solution 2
Maybe something like this will work for you?
package main
import "fmt"
import "time"
import "encoding/json"
type jsonTime struct {
t time.Time
f string
}
func (j jsonTime) MarshalText() ([]byte, error) {
return []byte(j.t.Format(j.f)), nil
}
func main() {
x := map[string]interface{}{
"foo": jsonTime{t: time.Now(), f: time.Kitchen},
"bar": "baz",
}
data, err := json.Marshal(x)
if err != nil {
panic(err)
}
fmt.Printf("%s", data)
}
also available here: http://play.golang.org/p/D1kq5KrXQZ
Just make a custom type that implements MarshalText the way you want it to show up.
Solution 3
First, I highly recommend against using a time format other than the default RFC3339. It's a good time format, and can be parsed by any number of languages, so unless you are needing a different format because somebody else's API requires it, it's probably best to use the default.
But, I've had to solve this problem in consuming other people's APIs, so here is one solution that shifts the bulk of the work to the Marshal/Unmarshal step, and leaves you with an ideal structure: http://play.golang.org/p/DKaTbV2Zvl
Ali
I love to build things that people love to use. I like scientific data analysis. I've spent most of my life in medicine and neuroscience! I like: vim, zsh, golang, debian, python I am addicted to writing code! and learning new things!!
Updated on June 04, 2022Comments
-
Ali almost 2 years
In Golang, is there a way to make the generic
encoding/json
Marshal to use a different layout when Marshaling thetime.Time
fields?Basically I have this struct:
s := {"starttime":time.Now(), "name":"ali"}
and I want to encoding to json using
encdoding/json
'sMarshal
function, but I want to use my custom layout, I imagine somewheretime.Format(layout)
is being called, I want to control that layout, -
Ali over 10 yearsThanks, That is definitely a step forward, but I wish I didn't have to convert all
time.Time
s tomytime
and back everytime I want to use a time.After or time.Before ... -
ChrisH over 10 yearsIf you want to call time.Time methods on the custom type, then embed a time.Time instead of giving it a name. e.g. play.golang.org/p/Vudw0hhnwe
-
Ali over 10 yearsUnless I am much mistaken, if I embed the
time.Time
then I theMarshalText
won't work for json encoding, which was the reason for all of this to begin with. It needs to be named. -
ChrisH over 10 yearsYes, embedding the time.Time does prevent MarshalText from working. Embedding promotes the MarshalJSON method of time.Time to the composite type. This can be overcome by overriding the MarshalJSON method as my example did. If you still want MarshalText for use by other encoders and you don't want to duplicate the formatting logic, then something like this might work: play.golang.org/p/liL0kAXp41
-
Ali over 10 years@chrisH you are right, why don't you post your solution as a answer.
-
themihai about 9 yearsHow is RFC3339 better than any other? (e.g RFC822Z)
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nojo over 8 yearshow would you make this respect "omitempty" on the time field?