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Teach you how to use Json in Go

藏色散人forward: 2021-12-28 15:44:211567browse

This article is provided by the golang tutorial column to introduce how to use Json in the Go language. I hope it will be helpful to friends in need!

Encode

Encode an object into JSON data, accepting an interface{} Object, returns []byte and error:

func Marshal(v interface{}) ([]byte, error)

Marshal The function will recursively traverse the entire object and evaluate the object by member type in turn. Encoding, the type conversion rules are as follows:

bool type conversion to JSONBoolean
Integers, floating point numbers and other numerical types are converted to JSONNumber
string Convert to a string of JSON (with "" quotes)
struct Convert to a of JSON Object, and then recursively pack the
array or slice into JSON’s Array
## based on the type of each member.
#[]byte will be base64 encoded first and then converted to JSON string
map converted to Object converted to JSON, key must be string
##interface{}
Convert according to the actual internal type
Convert to
JSONnull
##channel
func
and other types will return UnsupportedTypeError <pre class="brush:php;toolbar:false">type ColorGroup struct { ID int Name string Colors []string } group := ColorGroup{ ID: 1, Name: "Reds", Colors: []string{"Crimson", "Red", "Ruby", "Maroon"}, } b, err := json.Marshal(group) if err != nil { fmt.Println("error:", err) } os.Stdout.Write(b) Output: {"ID":1,"Name":"Reds","Colors":["Crimson","Red","Ruby","Maroon"]}</pre>

Decode

Decode JSONdata

func Unmarshal(data []byte, v interface{}) error

Type conversion rules and the above rules Similar to <pre class="brush:php;toolbar:false">var jsonBlob = []byte(`[ {"Name": "Platypus", "Order": "Monotremata"}, {"Name": "Quoll", "Order": "Dasyuromorphia"} ]`) type Animal struct { Name string Order string } var animals []Animal err := json.Unmarshal(jsonBlob, &animals) if err != nil { fmt.Println("error:", err) } fmt.Printf("%+v", animals) Output: [{Name:Platypus Order:Monotremata} {Name:Quoll Order:Dasyuromorphia}]</pre>

structure

The structure must be a member starting with a capital letter to be processed by JSON, Members starting with a lowercase letter have no effect.

Mashal, the member variable name of the structure will be directly packaged into ## as the

key

of JSON Object #JSON；Unmashal, the corresponding variable name will be automatically matched for assignment, and is not case-sensitive. When Unmarshal, if there are extra fields in JSON

, they will be discarded directly; if

JSON is missing a field, it will be discarded directly. Ignore not assigning values to variables in the structure and no error will be reported.

type Message struct { 
 Name string 
 Body string 
 Time int64 
 inner string 
} var m = Message{ 
 Name: "Alice", 
 Body: "Hello", 
 Time: 1294706395881547000, 
 inner: "ok", } b := []byte(`{"nAmE":"Bob","Food":"Pickle", "inner":"changed"}`) err := json.Unmarshal(b, &m) if err != nil { 
 fmt.Printf(err.Error()) 
 return} fmt.Printf("%v", m) Output: {Bob Hello 1294706395881547000 ok}

StructTag

If you want to manually configure the corresponding relationship between the members of the structure and the JSON field, you can define When labeling the structure, label the members:

Use

omitempty to be familiar with, if the field is nil

or 0 value (number 0, string "", empty array [], etc.), the packaged

JSON result will not have this field.

type Message struct { 
 Name string `json:"msg_name"`  // 对应JSON的msg_name 
 Body string `json:"body,omitempty"` // 如果为空置则忽略字段 
 Time int64 `json:"-"`    // 直接忽略字段 } var m = Message{ 
 Name: "Alice", 
 Body: "", 
 Time: 1294706395881547000, } data, err := json.Marshal(m) if err != nil { 
 fmt.Printf(err.Error()) 
 return} fmt.Println(string(data)) Output: {"msg_name":"Alice"}

More flexibility in using JSON

Use json.RawMessage

json .RawMessage is actually a redefinition of the []byte

type. Casting is possible.

Now there is a scenario where the format of one of the fields in the structure is unknown:

type Command struct { 
 ID int 
 Cmd string 
 Args *json.RawMessage 
}

If json.RawMessage is used,

Args# The ## field will not be parsed when

Unmarshal

, and the byte data will be assigned directly to Args. We can first unpack the JSON data of the first layer, and then determine the specific type of Args based on the value of Cmd for the second time Unmarshal. It should be noted here that you must use the pointer type *json.RawMessage, otherwise the Args will be considered

[]byte

Type will be packed into a base64 encoded string when packaging. Using interface{}

interface{}type will automatically Convert JSON to the corresponding data type:

JSON的boolean 转换为boolJSON的数值 转换为float64JSON的字符串 转换为stringJSON的Array 转换为[]interface{}JSON的Object 转换为map[string]interface{}JSON的null 转换为nil

There are two things to note. One is that all JSON values are automatically converted to the float64 type. When used, they need to be manually converted to the required int,

int64

and other types. . The second one is object of JSON which is automatically converted to map[string]interface{} type. When accessing, use JSON ``Object## directly. The field name of # is accessed as key. When you don’t know the format of JSON data, you can use interface{}.

自定义类型

如果希望自己定义对象的打包解包方式，可以实现以下的接口：

type Marshaler interface { 
 MarshalJSON() ([]byte, error) } type Unmarshaler interface { 
 UnmarshalJSON([]byte) error 
}

实现该接口的对象需要将自己的数据打包和解包。如果实现了该接口，json在打包解包时则会调用自定义的方法，不再对该对象进行其他处理。

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