007_custom_json_marshaling_and_unmarshaling

Go Sample Example - Custom JSON Marshaling and Unmarshaling

This repository demonstrates how to implement custom marshaling and unmarshaling for structs in Go. By overriding the MarshalJSON and UnmarshalJSON methods, you can customize how structs are converted to and from JSON format.

📖 Information

• This example covers how to override default JSON marshaling and unmarshaling for a struct in Go.
• It demonstrates custom formatting for fields during marshaling and parsing specific formats during unmarshaling.

💻 Code Example

package main

import (
	"encoding/json"
	"fmt"
	"strconv"
)

type Person7 struct {
	Name string
	Age  int
}

// Custom Marshaling for Person
func (p Person7) MarshalJSON() ([]byte, error) {
	return json.Marshal(struct {
		Name string `json:"name"`
		Age  string `json:"age"`
	}{
		Name: p.Name,
		Age:  strconv.Itoa(p.Age) + " years old",
	})
}

// Custom Unmarshaling for Person
func (p *Person7) UnmarshalJSON(data []byte) error {
	var aux struct {
		Name string `json:"name"`
		Age  string `json:"age"`
	}
	if err := json.Unmarshal(data, &aux); err != nil {
		return err
	}

	p.Name = aux.Name
	age, err := strconv.Atoi(aux.Age)
	if err != nil {
		return err
	}
	p.Age = age
	return nil
}

func main() {

	// This example shows how to implement custom marshaling and unmarshaling methods by overriding MarshalJSON and UnmarshalJSON for the Person struct

	person := Person7{
		Name: "John",
		Age:  30,
	}

	jsonData, err := json.Marshal(person)
	if err != nil {
		fmt.Println("Error encoding JSON:", err)
		return
	}

	fmt.Println("Custom Marshaled JSON:", string(jsonData))

	jsonString := `{"name":"Alice","age":"28"}`
	var newPerson Person7

	err = json.Unmarshal([]byte(jsonString), &newPerson)
	if err != nil {
		fmt.Println("Error decoding JSON:", err)
		return
	}

	fmt.Printf("Custom Unmarshaled Struct: %+v\n", newPerson)
}

🏃 How to Run

1. Make sure you have Go installed. If not, you can download it from here.

2. Clone this repository:

   git clone https://github.com/Rapter1990/go_sample_examples.git

3. Navigate to the 007_custom_json_marshaling_and_unmarshaling directory:

   cd go_sample_examples/030_json/007_custom_json_marshaling_and_unmarshaling

4. Run the Go program:

   go run 007_custom_json_marshaling_and_unmarshaling.go

📦 Output

When you run the program, you should see the following output:

Custom Marshaled JSON: {"name":"John","age":"30 years old"}
Custom Unmarshaled Struct: {Name:Alice Age:28}