Learn how to parse JSON objects with golang.

JavaScript Object Notation (JSON) is a data exchange format. While originally designed for JavaScript, these days many computer programs interact with the web and use JSON.

Interacting with the web is mostly done through APIs (Application Programmable Interface), in JSON format.

golang JSON example

Parse JSON

You can parse a JSON object with golang. The object will then be converted to a golang object.

Start by creating a json object

{
 "gold": 1271,
 "silver": 1284,
 "platinum": 1270
}

Then parse the JSON object like this:

package main

import (
    "encoding/json"
    "fmt"
)

func main() {
    // define data structure 
    type DayPrice struct {
      Gold int
      Silver int
      Platinum int
    }

    // json data
    data := `{"gold": 1271,"silver": 1284,"platinum": 1270}`        
    var obj DayPrice

    // unmarshall it
    err := json.Unmarshal([]byte(data), &obj)
    if err != nil {
        fmt.Println("error:", err)
    }

    // can access using struct now
    fmt.Printf("Gold     : $ %d\n", obj.Gold);
    fmt.Printf("Silver   : $ %d\n", obj.Silver);
    fmt.Printf("Platinum : $ %d\n", obj.Platinum);
}

Parse JSON from URL

You can get JSON objects directly from the web and convert them to golang objects. This is done through an API endpoint

package main

import "os"
import "fmt"
import "net/http"
import "io/ioutil"
import "encoding/json"

// Define data structure 
type Response struct {
  TradeID    int
  Price      string
  Size       string
  Bid        string
  Ask        string
  Volume     string
  Time       string
}


func get_content() {
  // json data
  url := "https://api.gdax.com/products/BTC-EUR/ticker"

  res, err := http.Get(url)

  if err != nil {
       panic(err.Error())
     }

    body, err := ioutil.ReadAll(res.Body)

    if err != nil {
         panic(err.Error())
       }

      var data Response

      // unmarshall
      json.Unmarshal(body, &data)
      //fmt.Printf("Results: %v\n", data)

      // print values of the object
      fmt.Printf("Price: $ %s\n", data.Price)      
      fmt.Printf("Price: $ %s\n", data.Bid)
      fmt.Printf("Price: $ %s\n", data.Ask)

      os.Exit(0)
}

func main() {
  get_content()
}