解码JSON值，可以是字符串或数字

Question

When I make an HTTP call to a REST API I may get the JSON value count back as a Number or String. I'ld like to marshal it to be an integer in either case. How can I deal with this in Go?.

Answer 1

Use the "string" field tag option to specify that strings should be converted to numbers. The documentation for the option is:

The "string" option signals that a field is stored as JSON inside a JSON-encoded string. It applies only to fields of string, floating point, integer, or boolean types. This extra level of encoding is sometimes used when communicating with JavaScript programs:

Here's an example use:

type S struct {
    Count int `json:"count,string"`
}

playground example

If the JSON value can be number or string, then unmarshal to interface{} and convert to int after unmarshaling:

Count interface{} `json:"count,string"`

Use this function to convert the interface{} value to an int:

func getInt(v interface{}) (int, error) {
  switch v := v.(type) {
  case float64:
    return int(v), nil
  case string:
    c, err := strconv.Atoi(v)
    if err != nil {
       return 0, err
    }
  default:
    return 0, fmt.Errorf("conversion to int from %T not supported", v)
  }
}