golang modify json file

Go language has now become a very popular language in the field of Internet development. It is efficient, concise, and easy to use. It also has good concurrency performance and supports network programming and other features. At the same time, another good feature of Golang is that it can operate JSON files very conveniently. We can easily read and modify JSON files in Go language.

In this article I will introduce how to use the standard library to modify JSON files in Golang. We will learn how to read JSON files, how to parse JSON data, how to modify JSON files in Golang and write the modified data back to the file.

Reading JSON files

It is very easy to read JSON files using the standard library in Golang. We only need to import the encoding/json and io/ioutil packages, use the ioutil.ReadFile function to read the JSON file, and then pass json.UnmarshalThe function parses the file content into JSON format.

For example, we have a JSON file named data.json with the following content:

{
    "name": "Jerry",
    "age": 25,
    "hobbies": ["reading", "running", "swimming"],
    "address": {
        "city": "New York",
        "state": "NY",
        "zip": "12345"
    }
}

We can read it using the following code:

package main

import (
    "fmt"
    "encoding/json"
    "io/ioutil"
)

type Person struct {
    Name     string   `json:"name"`
    Age      int      `json:"age"`
    Hobbies  []string `json:"hobbies"`
    Address  Address  `json:"address"`
}

type Address struct {
    City   string `json:"city"`
    State  string `json:"state"`
    Zip    string `json:"zip"`
}

func main() {
    file, _ := ioutil.ReadFile("data.json")
    var person Person
    json.Unmarshal([]byte(file), &person)
    fmt.Println(person)
}

In the above code, we define a Person structure and an Address structure to store data in the JSON file. Then read the file through the ioutil.ReadFile function and parse the JSON data using the json.Unmarshal function. Finally we print the output to the console.

The fields in the JSON file will automatically map to the fields of the corresponding structure. Here we use the tags of the Go language structure to match the fields in the JSON data. For example, the key name of the Name field in JSON is name, so we add the label json:" to the Name field in the structure." name".

Parsing JSON data

In the previous step, we have successfully parsed the JSON file into a Go language structure object. However, before we modify it, we need to understand how to obtain and modify data from the structure object.

In Golang, we use reflection to operate structures. Reflection is a mechanism that can dynamically obtain program type information and variable values ​​at runtime. We obtain the field information of the structure through reflection and modify the field values ​​of the structure.

The following code shows how to use reflection to get the value of the Name field in the Person structure and output:

package main

import (
    "fmt"
    "reflect"
)

type Person struct {
    Name string `json:"name"`
}

func main() {
    person := Person{
        Name: "Jerry",
    }
    value := reflect.ValueOf(person)
    fmt.Println(value.FieldByName("Name").String())
}

In the above code , we used the ValueOf function in the reflection package to obtain the value of the Person structure object, and used the FieldByName function to obtain the Name The value of the field.

Modify JSON data

Now that we know how to read JSON files and parse JSON data, next we will learn how to modify JSON data in Golang and rewrite it to JSON files .

Suppose we need to change the value of the Name field from Jerry to Tom, we can modify the JSON data as follows:

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
)

type Person struct {
    Name    string   `json:"name"`
    Age     int      `json:"age"`
    Hobbies []string `json:"hobbies"`
    Address Address  `json:"address"`
}

type Address struct {
    City  string `json:"city"`
    State string `json:"state"`
    Zip   string `json:"zip"`
}

func main() {
    file, _ := ioutil.ReadFile("data.json")
    var person Person
    json.Unmarshal([]byte(file), &person)

    person.Name = "Tom"

    newData, _ := json.Marshal(person)
    ioutil.WriteFile("data.json", newData, 0644)
    fmt.Println(string(newData))
}

In the above code, we first read the JSON file named data.json and use the json.Unmarshal function to parse the file content into a Person Go to the structure variable. Then we modify the value of the Name field from Jerry to Tom. Then we use the json.Marshal function to convert the structure object into a JSON string, and use the ioutil.WriteFile function to write the modified JSON data back to the original file.

Summary

In this article, we introduced how to manipulate JSON files in Golang. We learned how to read a JSON file, how to parse the JSON data, and how to modify the JSON data and write it back to the file. Golang is very convenient for processing JSON files. If you are not very familiar with Golang, it is recommended that you practice more. Mastering Golang can greatly improve your programming skills and experience.

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