Golang object to json

Converting an object to json in golang is a very common thing, I believe most golang developers will encounter it. This article will share the methods and techniques on how to convert an object into json in golang.

1. Using the encoding/json package

First look at the encoding/json package provided in the golang standard library. This package provides very simple and easy-to-use functions and types that allow us to easily convert an object into a json-formatted string or convert a json-formatted string into an object.

It should be noted that the object must be exportable (that is, the first letter is capitalized), otherwise the json package cannot access its fields.

The following is a simple example code that uses the encoding/json package to convert the Student object into a json format string:

package main

import (
    "encoding/json"
    "fmt"
)

type Student struct {
    Name  string
    Age   int
    Score float64
}

func main() {
    s := Student{
        Name:  "Tom",
        Age:   18,
        Score: 90.5,
    }
    b, err := json.Marshal(s)
    if err != nil {
        fmt.Println("json.Marshal failed:", err)
        return
    }
    fmt.Println(string(b))
}

Output:

{"Name":"Tom","Age":18,"Score":90.5}

As you can see, the json package provides The Marshal function can serialize a structure object into a json format string.

For a complex object, we can also easily serialize it into a json format string. For example, the following array consists of multiple Student objects:

package main

import (
    "encoding/json"
    "fmt"
)

type Student struct {
    Name  string
    Age   int
    Score float64
}

func main() {
    students := []Student{
        {Name: "Tom", Age: 18, Score: 90.5},
        {Name: "Jerry", Age: 19, Score: 96.5},
        {Name: "Alice", Age: 17, Score: 85.5},
    }
    b, err := json.Marshal(students)
    if err != nil {
        fmt.Println("json.Marshal failed:", err)
        return
    }
    fmt.Println(string(b))
}

Output:

[{"Name":"Tom","Age":18,"Score":90.5},{"Name":"Jerry","Age":19,"Score":96.5},{"Name":"Alice","Age":17,"Score":85.5}]

Similarly, we can use the Unmarshal function provided by the json package to parse a json format string into a object. For example:

package main

import (
    "encoding/json"
    "fmt"
)

type Point struct {
    X int `json:"x"`
    Y int `json:"y"`
}

type Line struct {
    Start Point `json:"start"`
    End   Point `json:"end"`
}

func main() {
    jsonStr := `
    {
        "start": {
            "x": 1,
            "y": 2
        },
        "end": {
            "x": 3,
            "y": 4
        }
    }`
    var line Line
    err := json.Unmarshal([]byte(jsonStr), &line)
    if err != nil {
        fmt.Println("json.Unmarshal failed:", err)
        return
    }
    fmt.Printf("%#v
", line)
}

Output:

main.Line{Start:main.Point{X:1, Y:2}, End:main.Point{X:3, Y:4}}

In this sample code, we define a Line object, which contains two Point objects. Use the Unmarshal function provided by the json package to parse a json format string into a Line object and then output it.

2. Customize json serialization and deserialization through structure tag

If we want to customize the output in json format, such as modifying the name of a field ,what can we do about it? At this time, the struct tag in golang comes in handy.

In golang, struct tag is a way to annotate struct fields, which can be achieved by adding a string after the field type. When using json package serialization and deserialization, we can use struct tag to control the serialization and deserialization process.

The following is a simple sample code that demonstrates how to use struct tag to control the process of json serialization and deserialization:

package main

import (
    "encoding/json"
    "fmt"
)

type Student struct {
    Name  string `json:"name"`
    Age   int    `json:"age"`
    Score float64
}

func main() {
    s := Student{
        Name:  "Tom",
        Age:   18,
        Score: 90.5,
    }
    fmt.Println("*** 序列化 ***")
    b, err := json.Marshal(s)
    if err != nil {
        fmt.Println("json.Marshal failed:", err)
        return
    }
    fmt.Println(string(b))

    fmt.Println("*** 反序列化 ***")
    jsonStr := `{"name":"Tom","age":18,"Score":90.5}`
    var student Student
    err = json.Unmarshal([]byte(jsonStr), &student)
    if err != nil {
        fmt.Println("json.Unmarshal failed:", err)
        return
    }
    fmt.Printf("%#v
", student)
}

Output:

*** 序列化 ***
{"name":"Tom","age":18,"Score":90.5}
*** 反序列化 ***
main.Student{Name:"Tom", Age:18, Score:90.5}

Here, we will The Name field in the Student object is marked as "name", so that when serialized using the json.Marshal function, its name will be changed to "name". Similarly, when deserializing using the json.Unmarshal function, "name" will be automatically recognized as the Name field.

Through the form of struct tag, we can also control the visibility of fields in the json output. For example:

package main

import (
    "encoding/json"
    "fmt"
)

type Student struct {
    Name  string `json:"name,omitempty"`
    Age   int    `json:"age"`
    Score float64
}

func main() {
    s := Student{
        Age:   18,
        Score: 90.5,
    }
    fmt.Println("*** 序列化 ***")
    b, err := json.Marshal(s)
    if err != nil {
        fmt.Println("json.Marshal failed:", err)
        return
    }
    fmt.Println(string(b))

    fmt.Println("*** 反序列化 ***")
    jsonStr := `{"name":"Tom","age":18,"Score":90.5}`
    var student Student
    err = json.Unmarshal([]byte(jsonStr), &student)
    if err != nil {
        fmt.Println("json.Unmarshal failed:", err)
        return
    }
    fmt.Printf("%#v
", student)
}

Output:

*** 序列化 ***
{"age":18,"Score":90.5}
*** 反序列化 ***
main.Student{Name:"Tom", Age:18, Score:90.5}

Here we mark the Name field as "omitempty", which means that if the value of the Name field is zero (i.e. ""), then when json is output Just ignore this field.

3. Using third-party libraries

When we need to perform more complex json serialization and deserialization, the golang standard library may be a little weak. At this time, we can use some third-party libraries to help us achieve more flexible operations.

The following is a sample code that uses a third-party library for json serialization and deserialization. This sample code uses the json-iterator/go package, which is currently one of the fastest golang json libraries.

package main

import (
    "fmt"
    "github.com/json-iterator/go"
)

type Student struct {
    Name  string `json:"name"`
    Age   int    `json:"age"`
    Score float64 `json:"score,omitempty"`
}

func main() {
    student := Student{
        Name:  "Tom",
        Age:   18,
        Score: 0,
    }
    fmt.Println("*** 序列化 ***")
    json := jsoniter.ConfigCompatibleWithStandardLibrary
    b, err := json.Marshal(student)
    if err != nil {
        fmt.Println("json.Marshal failed:", err)
        return
    }
    fmt.Println(string(b))

    fmt.Println("*** 反序列化 ***")
    jsonStr := `{"name":"Tom","age":18}`
    err = json.Unmarshal([]byte(jsonStr), &student)
    if err != nil {
        fmt.Println("json.Unmarshal failed:", err)
        return
    }
    fmt.Printf("%#v
", student)
}

Output:

*** 序列化 ***
{"name":"Tom","age":18}
*** 反序列化 ***
main.Student{Name:"Tom", Age:18, Score:0}

It should be noted that although using third-party libraries can achieve more flexible json operations, it may also introduce problems such as reduced performance or increased code complexity. The choice needs to be made based on specific scenarios.

This article introduces several methods and techniques for converting objects into json in golang. I hope this article can be helpful to readers.

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