Overview

encoding/json package provides utilities that can be used to convert to and from JSON. The same utility can be used to convert a golang map to JSON string and vice versa. A very important point to note though is that map allows integer values for keys while JSON doesn’t allow integer values for keys. JSON only allows string value for keys. So a map having an integer value for the key when converted to JSON will have a string value for the key.

Map to JSON

Let’s see a program for conversion of map to JSON

package main

import (
	"encoding/json"
	"fmt"
)

func main() {
	a := make(map[int]string)

	a[1] = "John"

	j, err := json.Marshal(a)
	if err != nil {
		fmt.Printf("Error: %s", err.Error())
	} else {
		fmt.Println(string(j))
	}
}

Output

{"1":"John"}

In the above code, we are using json.Marshal function to convert the map to JSON. The map has an integer value for the key

a := make(map[int]string)

While after converting, the resultant JSON as a string value for the key

{"1":"John"}

Let’s see one more example where we convert a map to a JSON where we have a struct for the value in the map. Below is the code for that

package main
import (
    "encoding/json"
    "fmt"
)
type employee struct {
    Name string
}
func main() {
    a := make(map[string]employee)
    a["1"] = employee{Name: "John"}
    j, err := json.Marshal(a)
    if err != nil {
        fmt.Printf("Error: %s", err.Error())
    } else {
        fmt.Println(string(j))
    }
}

Output

{"1":{"Name":"John"}}

JSON to map

Let’s try to convert from JSON to map. We will convert the resultant JSON from the above example back to the map.

json.Unmarshal function can be used to convert a JSON back to the map

First case:

package main

import (
	"encoding/json"
	"fmt"
)

func main() {
	a := make(map[int]string)

	a[1] = "John"

	j, err := json.Marshal(a)
	if err != nil {
		fmt.Printf("Error: %s", err.Error())
	} else {
		fmt.Println(string(j))
	}

	var b map[int]string
	json.Unmarshal(j, &b)

	fmt.Println(b)
}

Output

{"1":"John"}
map[1:John]

Second Case

package main
import (
    "encoding/json"
    "fmt"
)
type employee struct {
    Name string
}
func main() {
    a := make(map[string]employee)
    a["1"] = employee{Name: "John"}
    j, err := json.Marshal(a)
    if err != nil {
        fmt.Printf("Error: %s", err.Error())
    } else {
        fmt.Println(string(j))
    }
    var b map[int]employee
    json.Unmarshal(j, &b)
    fmt.Println(b)
}

Output

{"1":{"Name":"John"}}
map[1:{John}]