如何将json解码为结构

Question

我正在尝试在Go中解码一些json，但某些字段不会被解码。在此处查看在浏览器中运行的代码：

我究竟做错了什么？

我只需要MX记录，所以没有定义其他字段。据我从godoc了解到，您不需要定义不需要/不需要的字段。

// You can edit this code!
// Click here and start typing.
package main

import "fmt"
import "encoding/json"

func main() {

    body := `
  {"response": {
  "status": "SUCCESS",
  "data": {
    "mxRecords": [
      {
        "value": "us2.mx3.mailhostbox.com.",
        "ttl": 1,
        "priority": 100,
        "hostName": "@"
      },
      {
        "value": "us2.mx1.mailhostbox.com.",
        "ttl": 1,
        "priority": 100,
        "hostName": "@"
      },
      {
        "value": "us2.mx2.mailhostbox.com.",
        "ttl": 1,
        "priority": 100,
        "hostName": "@"
      }
    ],
    "cnameRecords": [
      {
        "aliasHost": "pop.a.co.uk.",
        "canonicalHost": "us2.pop.mailhostbox.com."
      },
      {
        "aliasHost": "webmail.a.co.uk.",
        "canonicalHost": "us2.webmail.mailhostbox.com."
      },
      {
        "aliasHost": "smtp.a.co.uk.",
        "canonicalHost": "us2.smtp.mailhostbox.com."
      },
      {
        "aliasHost": "imap.a.co.uk.",
        "canonicalHost": "us2.imap.mailhostbox.com."
      }
    ],
    "dkimTxtRecord": {
      "domainname": "20a19._domainkey.a.co.uk",
      "value": "\"v=DKIM1; g=*; k=rsa; p=DkfbhO8Oyy0E1WyUWwIDAQAB\"",
      "ttl": 1
    },
    "spfTxtRecord": {
      "domainname": "a.co.uk",
      "value": "\"v=spf1 redirect=_spf.mailhostbox.com\"",
      "ttl": 1
    },
    "loginUrl": "us2.cp.mailhostbox.com"
  }
}}`

    type MxRecords struct {
        value    string
        ttl      int
        priority int
        hostName string
    }



    type Data struct {
        mxRecords []MxRecords
    }

    type Response struct {
        Status string `json:"status"`
        Data   Data   `json:"data"`
    }
    type apiR struct {
        Response Response
    }

    var r apiR
    err := json.Unmarshal([]byte(body), &r)
    if err != nil {
        fmt.Printf("err was %v", err)
    }
    fmt.Printf("decoded is %v", r)

}

Answer 1

按照有关json.Unmarshal的go
documentaiton
所述，您只能对导出的字段进行解码，主要原因是外部软件包（例如encoding/json）无法访问未导出的字段。

如果您的json不遵循名称的go约定，则可以json在字段中使用标记来更改json键和struct字段之间的匹配。

范例：

package main

import (
    "fmt"
    "encoding/json"
)

type T struct {
    Foo string `json:"foo"`
}

func main() {
    text := []byte(`{"foo":"bar"}`)
    var t T
    err := json.Unmarshal(text, &t)
    if err != nil {
        panic(err)
    }
    fmt.Println(t)
}