无法将JSON解组到结构中

Question

I want to unmarshal the following JSON into a struct:

{"MAIN":{"data":[{"KEY1":"1111111","KEY2":"2222222","KEY3":0,"KEY4":"AAAAAAA","KEY5":"9999","KEY6":"4","KEY7":"BBBBBBB"}]}}

I have tried to modify the jsonStruct in various ways, but the struct is always empty:

package main

import (
    "encoding/json"
    "fmt"
)

type jsonStruct struct {
    main struct {
        data []struct {
            Key1 string `json:"KEY1"`
            Key2 string `json:"KEY2"`
            Key3 int    `json:"KEY3"`
            Key4 string `json:"KEY4"`
            Key5 string `json:"KEY5"`
            Key6 string `json:"KEY6"`
            Key7 string `json:"KEY7"`
       } `json:"data"`
    } `json:"MAIN"`
}

func main() {
    jsonData := []byte(`{"MAIN":{"data":[{"KEY1":"1111111","KEY2":"2222222","KEY3":0,"KEY4":"AAAAAAA","KEY5":"9999","KEY6":"4","KEY7":"BBBBBBB"}]}}`)

    var js jsonStruct

    err := json.Unmarshal(jsonData, &js)
    if err != nil {
            panic(err)
    }

    fmt.Println(js)
}

Output:

{{[]}}

The JSON I have worked with in the past contained no brackets, so I suspect that the problem is related to them.

Can anyone help?

https://play.golang.org/p/pymKbOqcM-

Answer 1

This is happening because other packages (encoding/json) can't access private fields (even with reflection). In go, private fields are fields starting with a lower case character. To fix this, make your struct contains public fields (which start with an upper case letter):

type jsonStruct struct {
    Main struct {
        Data []struct {
            Key1 string `json:"KEY1"`
            Key2 string `json:"KEY2"`
            Key3 int    `json:"KEY3"`
            Key4 string `json:"KEY4"`
            Key5 string `json:"KEY5"`
            Key6 string `json:"KEY6"`
            Key7 string `json:"KEY7"`
       } `json:"data"`
    } `json:"MAIN"`
}

https://play.golang.org/p/lStXAvDtpZ