部分JSON解组到Go中的地图

My websocket server will receive and unmarshal JSON data. This data will always be wrapped in an object with key/value pairs. The key-string will act as value identifier, telling the Go server what kind of value it is. By knowing what type of value, I can then proceed to JSON unmarshal the value into the correct type of struct.

Each json-object might contain multiple key/value pairs.

Example JSON:

{
    "sendMsg":{"user":"ANisus","msg":"Trying to send a message"},
    "say":"Hello"
}

Is there any easy way using the "encoding/json" package to do this?

package main

import (
    "encoding/json"
    "fmt"
)

// the struct for the value of a "sendMsg"-command
type sendMsg struct {
    user string
    msg  string
}
// The type for the value of a "say"-command
type say string

func main(){
    data := []byte(`{"sendMsg":{"user":"ANisus","msg":"Trying to send a message"},"say":"Hello"}`)

    // This won't work because json.MapObject([]byte) doesn't exist
    objmap, err := json.MapObject(data)

    // This is what I wish the objmap to contain
    //var objmap = map[string][]byte {
    //  "sendMsg": []byte(`{"user":"ANisus","msg":"Trying to send a message"}`),
    //  "say": []byte(`"hello"`),
    //}
    fmt.Printf("%v", objmap)
}

Thanks for any kind of suggestion/help!

This can be accomplished by Unmarshalling into a map[string]*json.RawMessage.

var objmap map[string]*json.RawMessage
err := json.Unmarshal(data, &objmap)

To further parse sendMsg, you could then do something like:

var s sendMsg
err = json.Unmarshal(*objmap["sendMsg"], &s)

For say, you can do the same thing and unmarshal into a string:

var str string
err = json.Unmarshal(*objmap["say"], &str)

EDIT: Keep in mind you will also need to export the variables in your sendMsg struct to unmarshal correctly. So your struct definition would be:

type sendMsg struct {
    User string
    Msg  string
}

Example: https://play.golang.org/p/RJbPSgBY6gZ

Further to Stephen Weinberg's answer, I have since implemented a handy tool called iojson, which helps to populate data to an existing object easily as well as encoding the existing object to a JSON string. A iojson middleware is also provided to work with other middlewares. More examples can be found at https://github.com/junhsieh/iojson

Example:

func main() {
    jsonStr := `{"Status":true,"ErrArr":[],"ObjArr":[{"Name":"My luxury car","ItemArr":[{"Name":"Bag"},{"Name":"Pen"}]}],"ObjMap":{}}`

    car := NewCar()

    i := iojson.NewIOJSON()

    if err := i.Decode(strings.NewReader(jsonStr)); err != nil {
        fmt.Printf("err: %s
", err.Error())
    }

    // populating data to a live car object.
    if v, err := i.GetObjFromArr(0, car); err != nil {
        fmt.Printf("err: %s
", err.Error())
    } else {
        fmt.Printf("car (original): %s
", car.GetName())
        fmt.Printf("car (returned): %s
", v.(*Car).GetName())

        for k, item := range car.ItemArr {
            fmt.Printf("ItemArr[%d] of car (original): %s
", k, item.GetName())
        }

        for k, item := range v.(*Car).ItemArr {
            fmt.Printf("ItemArr[%d] of car (returned): %s
", k, item.GetName())
        }
    }
}

Sample output:

car (original): My luxury car
car (returned): My luxury car
ItemArr[0] of car (original): Bag
ItemArr[1] of car (original): Pen
ItemArr[0] of car (returned): Bag
ItemArr[1] of car (returned): Pen