Golang：将 json 对象解组为一个切片

Question

I have JSON like

{
  "a": {"key": "a", "value": 1,},
  "b": {"key": "b", "value": 1,},
}

Is there a way to unmarshal it into []*struct {Key string; Value int} []*struct {Key string; Value int} , preserving the order of the structures?

If I unmarshal the JSON into map[string]*struct {Key string; Value int} map[string]*struct {Key string; Value int} and then convert the map into a slice, I'll lose the order of the structures.

Answer 1

To preserve order, use Decoder.Token and Decoder.More to walk through the top-level JSON object.

r := strings.NewReader(`
 {
   "a": {"key": "a", "value": 1},
   "b": {"key": "b", "value": 1}
 }`)

d := json.NewDecoder(r)
t, err := d.Token()
if err != nil || t != json.Delim('{') {
    log.Fatal("expected object")
}
var result []*element
for d.More() {
    k, err := d.Token()
    if err != nil {
        log.Fatal(err)
    }
    var v element
    if err := d.Decode(&v); err != nil {
        log.Fatal(err)
    }
    result = append(result, &v)
    fmt.Println("key:", k, "value:", v)
}

Run it on the Go Playground

Change the calls to log.Fatal to the error handling appropriate for your application.

This answer edits the JSON in the question to make the JSON valid.

The field names in the struct element type must be exported .

Answer 2

The easiest way that I found was to use jsonparser.ObjectEach :

import "github.com/buger/jsonparser"

...

var ss []*struct{Key string; Value int}
err = jsonparser.ObjectEach(data, func(key []byte, value []byte, dataType jsonparser.ValueType, offset int) error {
    var s struct{Key string; Value int}
    if err := json.Unmarshal(value, &s); err != nil {
        return err
    }
    *ss = append(*ss, &s)
    return nil
})

Answer 3

You could use the map[string]interface{} to unmarshal the json string. The code is this

func test() {
    jsonStr := `
 {
   "a": {"key": "a", "value": 1},
   "b": {"key": "b", "value": 1}
 }`
    var mapResult map[string]interface{}
    err := json.Unmarshal([]byte(jsonStr), &mapResult)
    if err != nil {
        fmt.Println("JsonToMapDemo err: ", err)
    }
    fmt.Println(mapResult)
}

the output is: map[a:map[key:a value:1] b:map[key:b value:1]]