> For the complete documentation index, see [llms.txt](https://minilabmemo.gitbook.io/golang-memo/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://minilabmemo.gitbook.io/golang-memo/advance-application/ge-shi/json.md). # json ### json tag * struct tag : field要大寫開頭，tag各有其功用 
+// Field appears in JSON as key "myName" 
+ and the field is omitted from the object if its value is empty,
NickName string `json:"nick_name,omitempty"` 
+//Field appears in JSON as key "Field" (大寫), but the field is skipped if empty.
Address string `json:",omitempty"` 
+// Field is ignored by this package.
A string `json:"-"` 
+// Field appears in JSON as key "-".
B string `json:"-,"` 
+//將輸出轉為string
AgeString int64 `json:"AgeString,string"`
### json Marshel * 返回 v 的 JSON 编码 * supported type See \[[json/encode](https://github.com/golang/go/blob/master/src/encoding/json/encode.go)] * 將struct 轉成 json string * Marshel如果字串含有HTML特殊字元會被轉換，如果不想要被轉換需要自己將EscapeHTML設為false
[線上範例](https://go.dev/play/p/GL8zgnPMKpv) ```go package main import ( "bytes" "encoding/json" "fmt" ) //field要大寫開頭，tag各有其功用 type UserDetail struct { Name string `json:"name"` NickName string `json:"nick_name,omitempty"` // Field appears in JSON as key "myName" and the field is omitted from the object if its value is empty, Address string `json:",omitempty"` //Field appears in JSON as key "Field" (大寫), but the field is skipped if empty. A string `json:"-"` // Field is ignored by this package. B string `json:"-,"` // Field appears in JSON as key "-". AgeString int64 `json:"AgeString,string"` //將輸出轉為string Age int64 `json:"Age"` } type User struct { Name string `json:"name"` } func main() { user1 := UserDetail{Name: "123", NickName: "123", Address: "123", A: "A", B: "B", AgeString: 123, Age: 12} jsonMarshal(user1) //-> json str: {"name":"123","my_name":"123","MyName2":"123","-":"B","int64string":"123","int64":123} value := make(chan int) //unsupportedTypeEncoder #ref1 jsonMarshal(value) //->Marshal err: json: unsupported type: chan int json str: user2 := User{Name: "

123

"} jsonMarshal(user2) //->json str: json str: {"name":"\u003ch1\u003e123\u003c/h1\u003e"} JsonMarshalEscapeHTMLfalse(user2) ->json str: {"name":"

123

"} } //struct to json string func jsonMarshal(u interface{}) { ub, err := json.Marshal(u) if err != nil { fmt.Println("Marshal err:", err) } fmt.Println("json str:", string(ub)) } func JsonMarshalEscapeHTMLfalse(u interface{}) { ub, err := JsonEscapeHTMLfalse(u) if err != nil { fmt.Println("JsonEscapeHTMLfalse err:", err) } fmt.Println("json str:", string(ub)) } func JsonEscapeHTMLfalse(t interface{}) ([]byte, error) { buffer := &bytes.Buffer{} encoder := json.NewEncoder(buffer) encoder.SetEscapeHTML(false) err := encoder.Encode(t) return buffer.Bytes(), err } o ```
### json.Unmarshal * 將json string轉為struct，需了解傳送過來json的結構, 利用type struct 去定義好之後再進行解析 * 利用 \`map\[string]interface{}\`轉換，但想要取資料解析後比較麻煩，不像是知道結構方便 * 可以用map取第一層，下一層需reflect，下下層也是...或是利用斷言 * 僅僅需要將某字串格式化可用 * 小地方注意：在进行反序列化操作时：第二个参数应该i传地址 ```diff +json.Unmarshal([]byte(data), &ns) -json.Unmarshal([]byte(data), ns) 出錯json: Unmarshal(non-pointer，也會出現毛毛蟲 -json: Unmarshal(non-pointer message.Message) -反序列化出错出现错误的原因是：在进行反序列化操作时：第二个参数应该i传地址 ```
(ex1):https://go.dev/play/p/kFzxUGvoDNJ ```go package main import ( "encoding/json" "fmt" ) type User struct { Name string `json:"name"` Age int64 `json:"Age"` Detail Detail `json:"detail"` } type Detail struct { Address string `json:"address"` } func main() { s := `{"name": "123", "age": 23, "detail": { "Address": "abd" } }` var d2 User //定義已知結構 if err := json.Unmarshal([]byte(s), &d2); err != nil { fmt.Println(err) } fmt.Println(d2) fmt.Println(d2.Detail.Address) //可以很輕鬆拿到內容 } ```
#### json.Compact 如果json string是beautify JSON String，json.Compact可以做壓縮。
範例 ```go /func main() { s := `{"name": "123", "age": 23, "detail": { "Address": "abd" } }` //json字串是 beautify JSON String minfy := compactJSON([]byte(s)) fmt.Println(string(minfy)) } //json.Compact func compactJSON(js []byte) []byte { buf := new(bytes.Buffer) if err := json.Compact(buf, js); err != nil { fmt.Println(err) return nil } return buf.Bytes() } ```
#### 轉換練習 * JSON String to String, string to JSON String * * beautify JSON String to String, string to JSON String *
#### reference | 來源 | 筆記 | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------- | |

What input will cause golang's json.Marshal to return an error?

|

json.Marshal types

e.g. func or chan refuse to serialize

| | [\[Golang JSON 處理\]](https://blog.dexiang.me/zh-tw/technologies/golang-json/\)) | | |

\[Golang中的读写数据（下）--JSON数据的编码与解码（筑基三层）]

|

struct tag 還可以有以下功能

printJson(key string, value interface{})

| | [Ｇolang — json Unmarshal 轉換碰上type interface {} does not support indexing](https://sam66.medium.com/%EF%BD%87olang-json-unmarshal-%E8%BD%89%E6%8F%9B%E7%A2%B0%E4%B8%8Atype-interface-does-not-support-indexing-48e6b03aa7c1)] | | | \[[还在用 map\[string\]interface{} 处理 JSON？告诉你一个更高效的方法——jsonvalue](https://segmentfault.com/a/1190000023564781) | | | [标准库 encoding/json 的进化之路](https://studygolang.com/articles/25100) | 各个 Go 版本中，标准库 encoding/json 的性能表现 在做出使用第三方序列化库替换标准库的决定前，最好先测试下 json 序列化和反序列化是否是应用的性能瓶颈点 | |

Go 语言中的深拷贝
copier 和 json 的性能

| TBD: 編按：雖然本文章說json性能較差 但go1.17實測jaon比較好？why? | | | |