Go (Golang) Struct JSON Tutorial - Convert Go Struct to / from JSON

In this tutorial, we will learn how to use JSON in Golang with examples.

JSON (JavaScript Object Notation) is a lightweight data interchange format.

In Golang, the encoding/json package implements the encoding and decoding of JSON.

Table of contents:

  • Go - Convert Struct to JSON
  • Go - Convert an array/slice into a JSON
  • Go - Convert JSON to Struct
  • Go - Convert JSON to an array/slice

Go - Convert Struct to JSON

In the example, we transform a Go struct into JSON format:


package main

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

type Employee struct {
    Id         int
    FirstName       string
    LastName string
    Email string
}

func main() {

    e1 := Employee{1, "John", "Cena", "john@gmail.com"}

    json_data, err := json.Marshal(e1)

    if err != nil {

        log.Fatal(err)
    }

    fmt.Println(string(json_data))
}

Output:

{"Id":1,"FirstName":"John","LastName":"Cena","Email":"john@gmail.com"}

We declare the Employee struct:


type Employee struct {
    Id         int
    FirstName       string
    LastName string
    Email string
}

We create the struct instance:


    e1 := Employee{1, "John", "Cena", "john@gmail.com"}

We encode the u1 struct into JSON with Marshal.


json_data, err := json.Marshal(e1)

Since json_data is a byte array, we convert it to a string with the string function:


fmt.Println(string(json_data))

Go - Convert an array/slice into a JSON

In the example, we transform a slice of structs into JSON format:


package main

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

type Employee struct {
    Id         int
    FirstName       string
    LastName string
	Email string
}

func main() {

    employees := []Employee{
        {Id: 2, FirstName: "Amir", LastName: "Khan", Email: "Amir@gmail.com"},
        {Id: 3, FirstName: "Lucy", LastName: "Smith", Email: "Smith@gmail.com"},
        {Id: 4, FirstName: "David", LastName: "Brown", Email: "David@gmail.com"},
    }

    json_data2, err := json.Marshal(employees)

    if err != nil {

        log.Fatal(err)
    }

    fmt.Println(string(json_data2))
}

Output:

[{"Id":2,"FirstName":"Amir","LastName":"Khan","Email":"Amir@gmail.com"},{"Id":3,"FirstName":"Lucy","LastName":"Smith","Email":"Smith@gmail.com"},{"Id":4,"FirstName":"David","LastName":"Brown","Email":"David@gmail.com"}]

The output can be pretty printed with the MarshalIndent function.


package main

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

type Employee struct {
    Id         int
    FirstName       string
    LastName string
	Email string
}

func main() {

    employees := []Employee{
        {Id: 2, FirstName: "Amir", LastName: "Khan", Email: "Amir@gmail.com"},
        {Id: 3, FirstName: "Lucy", LastName: "Smith", Email: "Smith@gmail.com"},
        {Id: 4, FirstName: "David", LastName: "Brown", Email: "David@gmail.com"},
    }

    json_data2, err := json.MarshalIndent(employees, "", "	")

    if err != nil {

        log.Fatal(err)
    }

    fmt.Println(string(json_data2))
}

Output:

[
	{
		"Id": 2,
		"FirstName": "Amir",
		"LastName": "Khan",
		"Email": "Amir@gmail.com"
	},
	{
		"Id": 3,
		"FirstName": "Lucy",
		"LastName": "Smith",
		"Email": "Smith@gmail.com"
	},
	{
		"Id": 4,
		"FirstName": "David",
		"LastName": "Brown",
		"Email": "David@gmail.com"
	}
]

Go - Convert JSON to Struct

In this source code example, we show how to convert JSON to Struct in Golang :


package main

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

type Employee struct {
    Id         int
    FirstName       string
    LastName string
	Email string
}

func main() {

    var e1 Employee

    data := []byte(`{"Id": 1, "FirstName": "John", "LastName": "Cena", "Email" : "john@gmail.com"}`)

    err := json.Unmarshal(data, &e1)

    if err != nil {

        log.Fatal(err)
    }

    fmt.Println("Struct is:", e1)
    fmt.Println("FirstName: ", e1.FirstName)
    fmt.Println("LastName: ", e1.LastName)
    fmt.Println("Email: ", e1.Email)
}

Output:

Struct is: {1 John Cena john@gmail.com}
FirstName:  John
LastName:  Cena
Email:  john@gmail.com

Go - Convert JSON to an array/slice

In this source code example, we show how to convert JSON to an array/slice in Golang with an example:


package main

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

type Employee struct {
    Id         int
    FirstName       string
    LastName string
	Email string
}

func main() {

    var employees []Employee

    data2 := []byte(`
    [
        {"Id": 1, "FirstName": "Amir", "LastName": "Khan", "Email": "Amir@gmail.com"},
        {"Id": 2, "FirstName": "Lucy", "LastName": "Smith", "Email": "Smith@gmail.com"},
        {"Id": 3, "FirstName": "David", "LastName": "Brown", "Email": "David@gmail.com"}
    ]`)

    err2 := json.Unmarshal(data2, &employees)

    if err2 != nil {

        log.Fatal(err2)
    }

    for i := range employees {

        fmt.Println(employees[i])
    }
}

Output:

{1 Amir Khan Amir@gmail.com}
{2 Lucy Smith Smith@gmail.com}
{3 David Brown David@gmail.com}

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