3 Easy Ways to Pretty Print JSON in Golang

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There are three ways to pretty print json in Go.

  1. Using “json.MarshalIndent()” function
  2. Using “json.Indent()” function
  3. Using “Encoder.SetIndent()” function

Method 1: Using json.MarshalIndent()

The easiest way to pretty print json in Golang is to use the “json.MarshalIndent()” method. The json.MarshalIndent() function takes in the interface we want to marshal as well as the prefix string and the indent string.

Example

package main

import (
  "encoding/json"
  "fmt"
)

func main() {
  sample_data := map[string]interface{}{
    "car": "Lamborghini",
    "company": "Volkswagen",
    "specs": map[string]string{
               "Fuel Type": "Petrol",
               "Transmission Type": "Automatic",
          },
  }
  formatted_data, err := json.MarshalIndent(sample_data, "", " ")
  
  if err != nil {
    fmt.Println(err)
    return
  }
  fmt.Println(string(formatted_data))
}

Output

{
  "car": "Lamborghini",
  "company": "Volkswagen",
  "specs": {
     "Fuel Type": "Petrol",
     "Transmission Type": "Automatic"
  }
}

The json.MarshalIndent() function accepts the JSON data(sample_data) as a byte slice and an optional prefix(“”) and indentation string(” “) and returns the indented JSON data as a byte slice.

Method 2: Using json.Indent()

The json.Indent() function is from a package json/encoding that beautifies the JSON string without indentation to JSON with indentation.

Example

package main

import (
  "bytes"
  "encoding/json"
  "log"
  "os"
)

func main() {
  type Company struct {
    Name string
    Number int
    Unit string
  }
  company := []Company{
      {"Lamborghini", 1, "million"},
      {"Buggati", 3, "million"},
  }

  bt, err := json.Marshal(company)
  if err != nil {
    log.Fatal(err)
  }

  var out bytes.Buffer
  json.Indent(&out, bt, "", " ")
  out.WriteTo(os.Stdout)
  println("\n")
}

Output

[
 {
   "Name": "Lamborghini",
   "Number": 1,
   "Unit": "million"
 },
 {
   "Name": "Buggati",
   "Number": 3,
   "Unit": "million"
 }
]

Method 3: Using Encoder.SetIndent()

The SetIndent() function instructs the encoder to format each subsequent encoded value as if indented by the package-level function. Using the json.Encode() function, you can set indentation through Encoder.SetIndent() method is similar to marshaling by defining a prefix and indent.

Example

package main

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

func PrettyString(str string) (string, error) {
  var prettyJSON bytes.Buffer
  if err := json.Indent(&prettyJSON, []byte(str), "", " "); err != nil {
    return "", err
  }
  return prettyJSON.String(), nil
}

func main() {
  animalJSON := `{"type": "Cat", "name": "Fluffy", "age": 5}`
  res, err := PrettyString(animalJSON)
  
  if err != nil {
    log.Fatal(err)
  }
  fmt.Println(res)
}

Output

{
  "type": "Cat",
  "name": "Fluffy",
  "age": 5
}

That’s it.

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