Golang通过JSON标记获取结构的字段名称

问题描述：

I have a struct:

type Human struct {
    Head  string  `json:"a1"`
    Body  string  `json:"a2"`
    Leg   string  `json:"a3"`
}

How can I get the struct's field name by providing JSON tag name? Probably something like this:

fmt.Println(getFieldName("a1")) // "Head"
fmt.Println(getFieldName("a2")) // "Body"
fmt.Println(getFieldName("a99")) // ""

func getFieldName(tag string) (fieldname string) {
    /* ... */
}

How should I implement the getFieldName function? I read online, it seems I need to use the reflect package, hmmm... any helping hand? :)

我有一个结构： p>

  type Human struct {\  n头字符串`json：“ a1”`
主体字符串`json：“ a2”`
腿部字符串`json：“ a3”`
} 
  code>  pre> 
 
 如何通过提供JSON标签名称来获取结构的字段名称？ 大概是这样的： p> 
 
   fmt.Println（getFieldName（“ a1”））//“ Head” 
fmt.Println（getFieldName（“ a2”））// // 正文“ 
fmt.Println（getFieldName（” a99“））//”“ 
 
func getFieldName（标签字符串）（字段名称字符串）{
 / * ... * / 
} 
  code>   pre> 
 
 我应该如何实现 getFieldName  code>函数？ 我在网上阅读，看来我需要使用 reflect  code>包，嗯……有什么帮助吗？  ：） p> 
  div>

答

You can use the reflect package to loop over a struct's fields and match against their tag values.

func getFieldName(tag, key string, s interface{}) (fieldname string) {
    rt := reflect.TypeOf(s)
    if rt.Kind() != reflect.Struct {
        panic("bad type")
    }
    for i := 0; i < rt.NumField(); i++ {
        f := rt.Field(i)
        v := strings.Split(f.Tag.Get(key), ",")[0] // use split to ignore tag "options" like omitempty, etc.
        if v == tag {
            return f.Name
        }
    }
    return ""
}

https://play.golang.com/p/2zCC7pZKJTz

Alternatively, as pointed out by @icza, you can build up a map and then use that for quicker lookups.

//                         Human            json       a1     Head
var fieldsByTag = make(map[reflect.Type]map[string]map[string]string)

func buildFieldsByTagMap(key string, s interface{}) {
    rt := reflect.TypeOf(s)
    if rt.Kind() != reflect.Struct {
        panic("bad type")
    }

    if fieldsByTag[rt] == nil {
        fieldsByTag[rt] = make(map[string]map[string]string)
    }
    if fieldsByTag[rt][key] == nil {
        fieldsByTag[rt][key] = make(map[string]string)
    }

    for i := 0; i < rt.NumField(); i++ {
        f := rt.Field(i)
        v := strings.Split(f.Tag.Get(key), ",")[0] // use split to ignore tag "options"
        if v == "" || v == "-" {
            continue
        }
        fieldsByTag[rt][key][v] = f.Name
    }
}

https://play.golang.com/p/qlt_mWsXGju

Golang通过JSON标记获取结构的字段名称

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