golang json insert comments

When developing with Golang, a very common requirement is to convert data into JSON format for storage or transmission. JSON is a lightweight, easy-to-read and write data format, and is widely used in web applications and mobile applications. However, in some cases, we may need to add annotations to the JSON data to enhance its readability or explain the meaning of certain fields, and the JSON standard itself does not support annotations. This article will introduce several ways to insert JSON comments with Golang.

Method 1: Use structure tags

In Golang, we usually use structure tags (tags) to define the mapping relationship of fields in JSON. For example, we can use json:"username" to map the structure field Name to the username field in JSON. In fact, it is allowed to use comments in structure tags. We only need to add json:"-" before the comment.

type User struct {
    Name     string `json:"username"`  // 用户名
    Password string `json:"password"`  // 密码
}

In the above example, we use // to add comments to describe the meaning of each field. When we convert the User structure to JSON, the comments will not affect the output. However, when decoding JSON into a structure, comments are ignored, which is not friendly to the rigor of the code.

Method 2: Use comment string

Another method is to add a comment string in JSON. This comment string is usually placed before the value of the JSON field. For example, we can add comments to the following JSON data:

{
    "user": {
        "name": "alice", // 用户名
        "password": "123456" // 密码
    }
}

In Golang, we can use the json.RawMessage type to represent the string value of JSON. This type can store unescaped JSON strings and does nothing with them when decoding. We can store the comment string in json.RawMessage and then add it to JSON.

Here is an example:

type User struct {
    Name     string `json:"-"`        // 不输出
    Password string `json:"-"`        // 不输出
    Comment  string `json:"comment"` // 注释
}

u := User{
    Name:     "alice",
    Password: "123456",
    Comment:  `{ "//username": "用户名", "//password": "密码" }`,
}

data, err := json.Marshal(u)
if err != nil {
    log.Fatal(err)
}

fmt.Println(string(data))

In the above example, we mark the user's username and password fields as -, indicating that they will not be output to JSON. The comment string is then stored in the Comment field. When converting the structure u to JSON format, we use the json.Marshal function to convert it to a JSON string. Finally, we output the JSON string to the console, and we can see that the comments in the JSON data have taken effect.

It should be noted that when decoding JSON data, we need to manually parse the comment string from the Comment field and interpret the JSON data based on its content. This will increase the complexity of the code, but it is also one of the currently feasible solutions.

Method 3: Using a third-party library

Finally, we can use a ready-made third-party library to insert JSON comments. Currently, there are some Golang JSON libraries that support adding comments, such as json-iterator/go and easyjson. These libraries support adding comments without affecting the JSON format and are very easy to use. convenient.

The following is an example of adding annotations using the json-iterator/go library:

import "github.com/json-iterator/go"

type User struct {
    Name     string `json:"username"`  // 用户名
    Password string `json:"password"`  // 密码
}

u := User{
    Name:     "alice",
    Password: "123456",
}

json := jsoniter.ConfigCompatibleWithStandardLibrary

data, err := json.Marshal(u)
if err != nil {
    log.Fatal(err)
}

fmt.Println(json.Get(data, "username").Last().GetInterface())

In the above example, we use jsoniter.ConfigCompatibleWithStandardLibrary Create a JSON object and use the Marshal function to convert the structure u into a JSON string. Finally, we use the json.Get function to get the specified field from JSON and the GetInterface function to convert it into a Golang object. Here we output the comment string corresponding to the username field to the console. You can see that the comment has been added successfully, and the code is relatively simple.

To sum up, the above are three ways to insert JSON comments in Golang. Each method has its advantages and disadvantages, and we should choose the most suitable method according to specific needs to enhance the readability of the code.

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