如何解组包含整数，浮点数和数字字符串的JSON？

Question

I have a multiple different JSON requests of data that is being passed into my Go app that contains numbers in different formats. An example of a request is as follows:

{
    "stringData":"123456",
    "intData": 123456,
    "floatData": 123456.0
}

Is there a way to unmarshal this data into the type which is determined by the JSON data. For example, string data would be "123456", int data would be 123456 and float data would be 123456.0. I do not have structs defined for these JSON objects and creating structs for these are not an option.

I have looked at the decoder.UseNumber() method to convert the data into strings, but I don't know how to handle the difference between stringData and intData after that.

Answer 1

Decode to map[string]interface{} with the UseNumber option. Use a type assertion to find numbers and convert based on presence of the ".".

dec := json.NewDecoder(r)
dec.UseNumber()

var m map[string]interface{}
err := dec.Decode(&m)
if err != nil {
    log.Fatal(err)
}

for k, v := range m {
    v, err := decodeValue(v)
    if err != nil {
        log.Fatal(err)
    }
for k, v := range m {
    v, err := decodeValue(v)
    if err != nil {
        log.Fatal(err)
    }
    switch v := v.(type) {
    case string:
        fmt.Printf("%s is a string with value %q
", k, v)
    case int64:
        fmt.Printf("%s is a integer with value %d
", k, v)
    case float64:
        fmt.Printf("%s is a float with value %f
", k, v)
    default:
        fmt.Printf("%s is a %T with value %v
", k, v, v)
    }
}


...

func decodeValue(v interface{}) (interface{}, error) {
    if vv, ok := v.(json.Number); ok {
        if strings.Contains(vv.String(), ".") {
            return vv.Float64()
        } else {
            return vv.Int64()
        }
    } else {
        return v, nil
    }
}

Run it on the playground.

This example prints what's found and exits the program on error. If your goal is to create a map with the values of the correct types, then replace the code that prints numbers with m[k] = n.