Example on custom UnmarshalJSON and MarshalJSON

marshalJSON_unmarshalJSON.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"strconv"
	"strings"
)

type Animal uint

const (
	CommonAnimal Animal = iota
	Zebra
	Gopher
)

func (a *Animal) String() string {
	switch *a {
	case Gopher:
		return "gopher"
	case Zebra:
		return "zebra"
	default:
		return "common-animal"
	}
}

func sToAnimal(s string) Animal {
	switch strings.ToLower(s) {
	case "gopher":
		return Gopher
	case "zebra":
		return Zebra
	default:
		return CommonAnimal
	}
}

func (a *Animal) UnmarshalJSON(b []byte) error {
	unquoted, err := strconv.Unquote(string(b))
	if err != nil {
		return nil
	}
	aAnimal := sToAnimal(unquoted)
	*a = aAnimal
	return nil
}

func (a *Animal) MarshalJSON() ([]byte, error) {
	quoted := strconv.Quote(a.String())
	return []byte(quoted), nil
}

func Example_marshalJSON() {
	zoo := []Animal{Gopher, Zebra, CommonAnimal, Gopher, Gopher, Zebra}
	marshaled, err := json.Marshal(&zoo)
	if err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%s", marshaled)

	// Output:
	// ["gopher","zebra","common-animal","gopher","gopher","zebra"]
}

func Example_unmarshalJSON() {
	rawZooManifest := `["zebra", "zebra", "common-animal", "gopher", "gopher"]`
	var zooManifest []*Animal
	if err := json.Unmarshal([]byte(rawZooManifest), &zooManifest); err != nil {
		log.Fatal(err)
	}

	fmt.Printf("%+v", zooManifest)
	// Output:
	// [zebra zebra common-animal gopher gopher]
}

func main() {
	Example_unmarshalJSON()
	Example_marshalJSON()
}