Implement MarshalJSON and UnmarshalJSON on a custom type

json-marshal.go

import (
	"fmt"
	"strings"
	"time"
)

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

// JSONTime a wrapper for time.Time that unmarshalls with a custom date format
type JSONTime struct {
	time.Time // anonymous field, struct inherits methods, refer to instance.Time
}

// UnmarshalJSON unmarshal JSON field to a JSONTime
func (t *JSONTime) UnmarshalJSON(buf []byte) error {
	tt, err := time.Parse(timeFormat, strings.Trim(string(buf), `"`))
	if err != nil {
		return err
	}
	t.Time = tt
	return nil
}

// MarshalJSON marshal JSONTime to a JSON field
func (t *JSONTime) MarshalJSON() ([]byte, error) {
	formatted := fmt.Sprintf("\"%s\"", t.Time.Format(timeFormat))
	return []byte(formatted), nil
}