Decode JSON to map[string]map[string]string - go

Question

I have a map[string]map[string]string that I'd like to be able to convert to JSON and write to a file, and be able to read the data back in from the file.
I've been able to successfully write to the file using the following:
func (l *Locker) Save(filename string) error {
file, err := os.Create(filename)
if err != nil {
return err
}
defer file.Close()
encoder := json.NewEncoder(file)
// l.data is of type map[string]map[string]string
return encoder.Encode(l.data)
}
I'm having trouble loading the JSON back into the map. I've tried the following:
func (l *Locker) Load(filename string) error {
file, err := os.Open(filename)
if err != nil {
return err
}
defer file.Close()
decoder := json.NewDecoder(file)
return decoder.Decode(l.data)
}
loading a JSON file with contents {"bar":{"hello":"world"},"foo":{"bar":"new","baz":"extra"}}, and after the above the contents of l.data is just map[]. How can I successfully decode this JSON into l.data?

Answer 1

If you use json.Unmarshal() instead you can pass it a data structure to populate. Here's a link to the code below, in the playground.
package main
import (
"fmt"
"encoding/json"
)
func main() {
src_json := []byte(`{"bar":{"hello":"world"},"foo":{"bar":"new","baz":"extra"}}`)
d := map[string]map[string]string{}
_ = json.Unmarshal(src_json, &d)
// Print out structure
for k, v := range d {
fmt.Printf("%s\n", k)
for k2, v2 := range v {
fmt.Printf("\t%s: %s\n", k2, v2)
}
}
fmt.Println("Hello, playground")
}