JSON Processing in Go (Golang): encoding/json and Alternatives

JSON Processing in Go (Golang): From Basics to Advanced Techniques

Go (Golang) offers a powerful and intuitive set of tools for working with JSON. The standard library encoding/json covers 95% of tasks, and for high-load projects, there are more performant alternatives. In this article, we will cover all aspects of JSON processing in Go: from basic serialization to custom parsers and optimization.

1. Basics: The Standard Library encoding/json

In Go, JSON is processed through the encoding/json package. The main operations are marshaling (serialization to JSON) and unmarshaling (deserialization from JSON).

1.1. Marshaling (struct → JSON)

To convert a Go struct to JSON, use the json.Marshal() function:

package main

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

type User struct {    Name  string `json:"name"`    Age   int    `json:"age"`    Email string `json:"email,omitempty"` // omitempty - skip if empty}

func main() {    user := User{        Name:  "Ivan Petrov",        Age:   30,        Email: "ivan@example.com",    }

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

    fmt.Println(string(jsonData))    // {"name":"Ivan Petrov","age":30,"email":"ivan@example.com"}}

Important: Struct fields must be exported (start with a capital letter). The json:"fieldname" tags control the field names in JSON.

1.2. Unmarshaling (JSON → struct)

For the reverse transformation, use json.Unmarshal():

func main() {    jsonString := `{"name":"Anna","age":25,"email":"anna@mail.com"}`        var user User    err := json.Unmarshal([]byte(jsonString), &user)    if err != nil {        log.Fatal(err)    }

    fmt.Printf("Name: %s, Age: %d", user.Name, user.Age)    // Name: Anna, Age: 25}

2. Working with Nested Structures and Arrays

JSON often contains nested objects and arrays. In Go, this maps to nested structs and slices:

type Address struct {    City    string `json:"city"`    Street  string `json:"street"`    ZipCode string `json:"zip_code"`}

type Company struct {    Name      string    `json:"name"`    Employees []User    `json:"employees"`    Address   Address   `json:"address"`}

func main() {    companyJSON := `{        "name": "TechCorp",        "employees": [            {"name":"Oleg","age":28,"email":"oleg@tech.com"},            {"name":"Maria","age":32,"email":"maria@tech.com"}        ],        "address": {            "city": "Moscow",            "street": "Tverskaya, 10",            "zip_code": "101000"        }    }`

    var company Company    json.Unmarshal([]byte(companyJSON), &company)    fmt.Printf("Company: %s, City: %s, Employees: %d",        company.Name, company.Address.City, len(company.Employees))}

3. Advanced Techniques

3.1. Custom Serialization (Marshaler/Unmarshaler Interfaces)

Sometimes you need to control how a type is converted to JSON. To do this, implement the json.Marshaler and json.Unmarshaler interfaces:

type CustomTime struct {    time.Time}

const layout = "2006-01-02T15:04:05Z"

func (ct CustomTime) MarshalJSON() ([]byte, error) {    return json.Marshal(ct.Format(layout))}

func (ct *CustomTime) UnmarshalJSON(data []byte) error {    var s string    if err := json.Unmarshal(data, &s); err != nil {        return err    }    t, err := time.Parse(layout, s)    if err != nil {        return err    }    ct.Time = t    return nil}

type Event struct {    Title string     `json:"title"`    Date  CustomTime `js