有Json标记，但未导出[重复]

Question

This question already has an answer here:

• JSON and dealing with unexported fields 2 answers
• (un)marshalling json golang not working 2 answers

Begining to study golang. Task: Get Json and Unmarshall it. But I get mistake:

Json tag but not exported

How to make unexported fields become exported and then implement it using methods?

Here is the code:

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
)

type Time struct {
    time
}
type time struct {
    id                    string  `json:"$id"`
    currentDateTime       string  `json:"currentDateTime,string"`
    utcOffset             float64 `json:"utcOffset,string"`
    isDayLightSavingsTime bool    `json:"isDayLightSavingsTime,string"`
    dayOfTheWeek          string  `json:"dayOfTheWeek,string"`
    timeZoneName          string  `json:"timeZoneName,string"`
    currentFileTime       float64 `json:"currentFileTime,string"`
    ordinalDate           string  `json:"ordinalDate,string"`
    serviceResponse       string  `json:"serviceResponse,string"`
}

func (t *Time) GetTime() (Time, error) {
    result := Time{}

    return result, t.Timenow(result)
}
func (t *Time) Timenow(result interface{}) error {

    res, err := http.Get("http://worldclockapi.com/api/json/utc/now")
    if err != nil {
        fmt.Println("Cannot get Json", err)
    }

    body, err := ioutil.ReadAll(res.Body)
    if err != nil {
        fmt.Println("Cannot create Body", err)
    }

    defer res.Body.Close()

    var resultJson interface{}
    return json.Unmarshal(body, &resultJson)

}

func main() {

    var a Time
    t, err := a.GetTime()
    if err != nil {
        fmt.Println("Error ", err)
    }
    fmt.Println("Time:", t)
}

Please explain in details whats wrong with struct and how to get right response?

</div>

Answer 1

You're adding a JSON tag to a field that isn't exported.

Struct fields must start with upper case letter (exported) for the JSON package to see their value.

struct A struct {
    // Unexported struct fields are invisible to the JSON package.
    // Export a field by starting it with an uppercase letter.
    unexported string

    // {"Exported": ""}
    Exported string

    // {"custom_name": ""}
    CustomName string `json:"custom_name"`
}

The underlying reason for this requirement is that the JSON package uses reflect to inspect struct fields. Since reflect doesn't allow access to unexported struct fields, the JSON package can't see their value.