Golang : Decode/unmarshal unknown JSON data type with map[string]interface

Tags : golang json map interface unmarshal decode

This tutorial is courtesy of Rohan Allison on how to decode or unmarshal JSON into map[string]interface. There are times we only know in advance that the top-level keys are in string type and not the data type.

So how to handle the data type? Golang doesn't support generic yet. Aha! interface can handle the unknown data type.

Here you go!

 package main

 import "fmt"
 import "encoding/json"

 func main() {
  // Given a possibly complex JSON object
  msg := "{\"assets\" : {\"old\" : 123}}"

  // We only know our top-level keys are strings
  mp := make(map[string]interface{})

  // Decode JSON into our map
  err := json.Unmarshal([]byte(msg), &mp)
  if err != nil {

  // See what the map has now
  fmt.Printf("mp is now: %+v\n", mp)

  // Iterate the map and print out the elements one by one
  // Note: that mp has to be deferenced here or range will fail
  for key, value := range mp {
 fmt.Println("key:", key, "value:", value)

Output :

mp is now: map[assets:map[old:123]]

key: assets value: map[old:123]


Happy coding! and once again thanks to Mr. Rohan Allison for the code example!

Reference :


Tags : golang json map interface unmarshal decode

By Adam Ng

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