Customizing JSON Layout for time.Time in Golang

In Golang, the encoding/json.Marshal function is commonly used to convert objects to JSON. However, under default settings, it may not align with the desired JSON layout. This article illustrates a solution to override the default layout and customize the format used by time.Time fields during JSON marshalling.

Let's assume you have a struct s with a time.Time field named starttime. When marshalling this struct to JSON, you want to use a specific custom layout.

s := {"starttime":time.Now(), "name":"ali"}

To achieve this, we can create a custom type that embeds time.Time and overrides both MarshalText and MarshalJSON methods.

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
}

By overriding MarshalText, we control how the jsonTime type converts its value to a text form, allowing us to specify the custom layout. Additionally, by overriding MarshalJSON, we ensure the overridden method is used instead of the built-in time.Time implementation for JSON marshalling.

With the custom jsonTime type, you can now marshal your s struct using the desired layout:

jt := jsonTime{time.Now(), time.Kitchen}
x := map[string]interface{}{
    "foo": jt,
    "bar": "baz",
}
data, err := json.Marshal(x)
if err != nil {
    panic(err)
}

This will produce a JSON string with the starttime field formatted according to the time.Kitchen layout.