How to create custom JSON encoder in Golang?

To create a custom JSON encoder in Golang: implement the encoding/json.Marshaler or encoding/json.Unmarshaler interface. The Marshaler interface provides a method to convert a structure into JSON bytes. The Unmarshaler interface provides a method to decode a structure from JSON bytes.

Create a custom JSON encoder in Golang

JSON is a popular method for transmitting data over the network. Format. In Golang, structures can be easily encoded and decoded using the standard library encoding/json. However, sometimes you may need to create a custom encoder to meet specific needs.

Implementing a custom JSON encoder

In order to implement a custom JSON encoder, you need to implement encoding/json.Marshaler or encoding/json.Unmarshaler interface. The

• Marshaler interface defines a MarshalJSON method that converts a structure to JSON bytes. The
• Unmarshaler interface defines an UnmarshalJSON method that decodes a structure from JSON bytes.

Here's how to implement a custom JSON encoder:

type User struct {
    ID   int
    Name string
}

// 实现 Marshaler 接口
func (u User) MarshalJSON() ([]byte, error) {
    return []byte(`{"user_id": ` + strconv.Itoa(u.ID) + `,"name": "` + u.Name + `"}`), nil
}

// 实现 Unmarshaler 接口
func (u *User) UnmarshalJSON(data []byte) error {
    var v map[string]interface{}
    if err := json.Unmarshal(data, &v); err != nil {
        return err
    }
    id, ok := v["user_id"].(float64)
    if !ok {
        return fmt.Errorf("invalid user_id")
    }
    u.ID = int(id)
    u.Name = v["name"].(string)
    return nil
}

This encoder encodes and decodes the User structure into JSON fields with a specific format. user_id is encoded as an integer, while name is encoded as a string.

Practical case

In the following example, we use a custom encoder to convert the User structure to JSON bytes:

// 创建一个 User 结构
u := User{
    ID:   1,
    Name: "John Doe",
}

// 转换为 JSON 并打印
jsonBytes, err := json.Marshal(u)
if err != nil {
    panic(err)
}
fmt.Println(string(jsonBytes))

Output:

{"user_id": 1,"name": "John Doe"}

By creating a custom JSON encoder, you can control the format and content of JSON data according to your needs.

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