Example for changing default JSON marshalling-unmarshalling

Go custom JSON marshal-unmarshal

Naming file

json.go

// Structure for marshalling/unmarshalling
type Message struct {
    Id   int        `json:"id"`
    Date time.Time  `json:"date"`
}

// Custom marshalling: date field will be converted
// to int64 (unix timestamp)
func (m *Message) MarshalJSON() ([]byte, error) {
    type Alias Message
    return json.Marshal(&struct {
        Date int64 `json:"date"`
        *Alias
    }{
        SendDate: m.Date.Unix(),
        Alias:    (*Alias)(m),
    })
}

// Custom unmarshalling: date field will be converted
// from integer (unix timestamp) to time.Time
func (m *Message) UnmarshalJSON(data []byte) error {
    type Alias Message

    tmp := &struct {
        Date int64 `json:"date"`
        *Alias
    }{
        Alias: (*Alias)(m),
    }

    if err := json.Unmarshal(data, &tmp); err != nil {
        return err
    }
    m.Date = time.Unix(tmp.Date, 0)
    return nil
}

func main() {
    m := Message{
        Id: 10,
        Date: time.Now(),
    }
    j := json.Marshal(&m)
    u := json.Unmarshal(j)
}