map[string]interface{}
通过同一通道交换多种信息的时候,我们经常需要 JSON 具有动态的,或者更合适的参数内容。首先,让我们来讨论一下消息封装(message envelopes),JSON 在这里看起来就像这样:
{
"type": "this part tells you how to interpret the message",
"msg": ...the actual message is here, in some kind of json...
}
通过不同的消息类型生成 JSON
interface{}
{
"type": "sound",
"msg": {
"description": "dynamite",
"authority": "the Bruce Dickinson"
}
}
{
"type": "cowbell",
"msg": {
"more": true
}
}
我们可以使用这些 Go 类型:
package main
import (
"encoding/json"
"fmt"
"log"
)
type Envelope struct {
Type string
Msg interface{}
}
type Sound struct {
Description string
Authority string
}
type Cowbell struct {
More bool
}
func main() {
s := Envelope{
Type: "sound",
Msg: Sound{
Description: "dynamite",
Authority: "the Bruce Dickinson",
},
}
buf, err := json.Marshal(s)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s\n", buf)
c := Envelope{
Type: "cowbell",
Msg: Cowbell{
More: true,
},
}
buf, err = json.Marshal(c)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%s\n", buf)
}
输出的结果是:
{"Type":"sound","Msg":{"Description":"dynamite","Authority":"the Bruce Dickinson"}}
{"Type":"cowbell","Msg":{"More":true}}
这些并没有什么特殊的。
解析 JSON 到动态类型
EnvelopeMsgmap[string]interface{}
package main
import (
"encoding/json"
"fmt"
"log"
)
const input = `
{
"type": "sound",
"msg": {
"description": "dynamite",
"authority": "the Bruce Dickinson"
}
}
`
type Envelope struct {
Type string
Msg interface{}
}
func main() {
var env Envelope
if err := json.Unmarshal([]byte(input), &env); err != nil {
log.Fatal(err)
}
// for the love of Gopher DO NOT DO THIS
var desc string = env.Msg.(map[string]interface{})["description"].(string)
fmt.Println(desc)
}
输出:
dynamite
明确的解析方式
Envelope
type Envelope {
Type string
Msg *json.RawMessage
}
[]byte
MsgTypeTypeMsgEnvelopeInEnvelopeOutEnvelopeOutMsg interface{}
*json.RawMessageinterface{}
interface{}*json.RawMessage
package main
import (
"encoding/json"
"fmt"
"log"
)
const input = `
{
"type": "sound",
"msg": {
"description": "dynamite",
"authority": "the Bruce Dickinson"
}
}
`
type Envelope struct {
Type string
Msg interface{}
}
type Sound struct {
Description string
Authority string
}
func main() {
var msg json.RawMessage
env := Envelope{
Msg: &msg,
}
if err := json.Unmarshal([]byte(input), &env); err != nil {
log.Fatal(err)
}
switch env.Type {
case "sound":
var s Sound
if err := json.Unmarshal(msg, &s); err != nil {
log.Fatal(err)
}
var desc string = s.Description
fmt.Println(desc)
default:
log.Fatalf("unknown message type: %q", env.Type)
}
}
输出:
dynamite
如何把所有数据都放在最外层(顶层)
虽然我极其推荐你将动态可变的部分放在一个单独的 key 下面,但是有时你可能需要处理一些预先存在的数据,它们并没有用这样的方式进行格式化。
如果可以的话,请使用文章前面提到的风格。
{
"type": "this part tells you how to interpret the message",
...the actual message is here, as multiple keys...
}
我们可以通过解析两次数据的方式来解决。
package main
import (
"encoding/json"
"fmt"
"log"
)
const input = `
{
"type": "sound",
"description": "dynamite",
"authority": "the Bruce Dickinson"
}
`
type Envelope struct {
Type string
}
type Sound struct {
Description string
Authority string
}
func main() {
var env Envelope
buf := []byte(input)
if err := json.Unmarshal(buf, &env); err != nil {
log.Fatal(err)
}
switch env.Type {
case "sound":
var s struct {
Envelope
Sound
}
if err := json.Unmarshal(buf, &s); err != nil {
log.Fatal(err)
}
var desc string = s.Description
fmt.Println(desc)
default:
log.Fatalf("unknown message type: %q", env.Type)
}
}
dynamite
译者:
校对:
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