JSON Decoding in Go (golang)

A quick example of JSON decoding (or unmarshaling) in Go. This is basically magic, it’s totally amazing I love it.

It’s possible to decode the JSON into generic maps, but if you know the structure you can get the JSON to populate native go structures automatically. You need to be mindful of types, go wont for example convert an int to a string, it’ll just ignore it.

This means if you have a JSON object that contains string:int key values and string:string key values and you try to populate a golang string map from it, you’ll lose all you string:int pairs. You are better off creating a struct to represent it as seen below.

package main

import (
	"encoding/json"
	"fmt"
)

type LogEntry struct {
	Time string
	Cpm		float32
	Duration	int32
	Accel_x_start	int32
	Accel_y_start	int32
	Accel_z_start	int32
	Accel_x_end	int32
	Accel_y_end	int32
	Accel_z_end	int32
}

type Log struct {
  Log_size 			int
	Onyx_version 	string
	UTC_offset		string
	Log_data			[] LogEntry

}

func main() {

	b := []byte(`{"log_size":61,"onyx_version":"pre11","UTC_offset":"undef","log_data":[{"time":"2012-10-23T22:23:54Z","cpm":46,"duration":30,"accel_x_start":-4,"accel_y_start":-97,"accel_z_start":-3,"accel_x_end":-1,"accel_y_end":-98,"accel_z_end":-2}]}`)	

	var l Log
	json.Unmarshal(b, &l)

  fmt.Printf("logsize: %d onyxversion: %s data1: %s\n",l.Log_size,l.Onyx_version,l.Log_data[0]);
}

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