从JSON字符串值解析JSON

Question

I want to convert from string to object.

From

{"key1": "{
  \"key2\": \"value2\",
  \"key3\": {
    \"key4\": \"value4\"
  }
}
"}

To

{"key1": {"key2": "value2", "key3": {"key4": "value4"}}}

Finally, I want to get value4.

I can get the value of "key1" using below script.

jsondata := `{"key1": "{
  \"key2\": \"value2\",
  \"key3\": {
    \"key4\": \"value4\"
  }
}
"}`
var m map[string]interface{}
json.Unmarshal([]byte(jsondata), &m)
value := m["key1"]
fmt.Println(value)

https://play.golang.org/p/4lwgQJfp5S

But I can't convert the value to an object. So I can't get "value4". Are there methods for this? I can get it by regex like https://play.golang.org/p/6TB-qNAdgQ But now this is not my solution.

Thank you so much for your time and advices. And I'm sorry for my immature question.

Answer 1

There are two levels of JSON encoding. The first step is to decode the outer JSON value. Decode to a struct matching the structure of the JSON.

var outer struct{ Key1 string }
if err := json.Unmarshal([]byte(jsondata), &outer); err != nil {
    log.Fatal(err)
}

The next step is to decode the inner JSON value. Again, decode to a struct matching the structure of the JSON.

var inner struct{ Key3 struct{ Key4 string } }
if err := json.Unmarshal([]byte(outer.Key1), &inner); err != nil {
    log.Fatal(err)
}
// The value is inner.Key3.Key4

playground example

If the JSON is not double encoded, you can decode in one shot:

jsondata := `{"key1": { "key2": "value2",  "key3": { "key4": "value4"  }}}`
var v struct {
    Key1 struct{ Key3 struct{ Key4 string } }
}
if err := json.Unmarshal([]byte(jsondata), &v); err != nil {
    log.Fatal(err)
}
// value is v.Key1.Key3.Key4

playground example