Go语言标准库之JSON编解码

Go语言中的数据类型和JSON的数据类型的关系

bool -> JSON boolean

float64 -> JSON numbers

string -> JSON strings

nil -> JSON null

Struct to JSON

Go包encoding/json中的json.Marshal方法，可以将struct编码为JSON数据

package main import ( "encoding/json" "fmt" "time" ) type FruitBasket struct { Name string Fruit []string Id int64 `json:"ref"` private string // 这个字段不会被编码 Created time.Time } func main() { basket := FruitBasket{ Name: "Standard", Fruit: []string{"Apple", "Banana", "Orange"}, Id: 999, private: "Second-rate", Created: time.Now(), } jsonData, err := json.Marshal(basket) if err != nil { fmt.Println(err) } fmt.Println(string(jsonData)) }

输出结果

{"Name":"Standard","Fruit":["Apple","Banana","Orange"],"ref":999,"Created":"2019-01-01T11:40:05.9885387+08:00"}

只有public字段才能被导出

json:tag可以定义导出字段的名称

nil导出为null

格式化输出

可以使用json.MarshalIndent方法来格式化输出的JSON数据

formatData, err := json.MarshalIndent(basket, "", " ") fmt.Println(string(formatData))

格式化输出结果是

{ "Name": "Standard", "Fruit": [ "Apple", "Banana", "Orange" ], "ref": 999, "Created": "2019-01-01T11:45:49.0969176+08:00" }

JSON to Struct

Go包中json.Unmarshal方法，解析 JSON数据

jsonStr := []byte(` { "Name": "Standard", "Fruit": [ "Apple", "Banana", "Orange" ], "ref": 999, "Created": "2019-01-01T11:45:49.0969176+08:00" } `) var basketStruct FruitBasket err = json.Unmarshal(jsonStr, &basketStruct) if err != nil { log.Println(err) } fmt.Println(basketStruct.Name, basketStruct.Fruit) fmt.Println(basketStruct.Created)

输出结果是

Standard [Apple Banana Orange] 2019-01-01 11:45:49.0969176 +0800 CST

编码格式化任意类型的对象和数组

map[string]interface{}可以编码任意类型的 JSON对象
[]interface{}可以编码任意类型的JSON数组

arbitData := []byte(`{"Name":"Eve","Age":6,"Parents":["Alice","Bob"]}`) var v interface{} err = json.Unmarshal(arbitData, &v) if err != nil { log.Println(err) } data := v.(map[string]interface{}) for k, v := range data { switch v := v.(type) { case string: fmt.Println(k, v, "(string)") case float64: fmt.Println(k, v, "(float64)") case []interface{}: fmt.Println(k, v, "(array)") for i, u := range v { fmt.Println(" ", i, u) } default: fmt.Println(k, v, "(unknown)") } }

输出结果是

Name Eve (string) Age 6 (float64) Parents [Alice Bob] (array) 0 Alice 1 Bob

编解码JSON文件

Go中encoding/json中的json.Decoder和json.Encoder方法可以编解码JSON格式文件

例子：

jsonstr := ` {"Name": "Alice", "Age": 25} {"Name": "Bob", "Age": 22}` reader := strings.NewReader(jsonstr) writer := os.Stdout dec := json.NewDecoder(reader) enc := json.NewEncoder(writer) for { var m map[string]interface{} if err := dec.Decode(&m); err == io.EOF { break } else if err != nil { log.Fatal(err) } for k := range m { if k == "Age" { delete(m, k) } } if err = enc.Encode(&m); err != nil { log.Println(err) } }

输出结果是

{"Name":"Alice"} {"Name":"Bob"}

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