Working with JSON in Dart: Complete Beginner’s Guide

Working with JSON in Dart is essential for building modern mobile or web applications using Flutter or Dart. JSON (JavaScript Object Notation) is a popular data format for exchanging information between servers and clients. In Dart, handling JSON is straightforward using built-in dart:convert package which provides jsonEncode and jsonDecode functions.

This article will walk you through parsing JSON from a string, mapping JSON to a custom Dart class, and encoding a Dart object back into a JSON string.

1. Importing Required Library

import 'dart:convert';

2. Sample JSON Data

Here’s a simple JSON data string we want to decode:

{
  "name": "John Doe",
  "email": "john@example.com",
  "age": 28
}

3. Dart Class to Map JSON

Create a model class that mirrors the structure of the JSON.

class User {
  final String name;
  final String email;
  final int age;

  User({required this.name, required this.email, required this.age});

  factory User.fromJson(Map<String, dynamic> json) {
    return User(
      name: json['name'],
      email: json['email'],
      age: json['age'],
    );
  }

  Map<String, dynamic> toJson() {
    return {
      'name': name,
      'email': email,
      'age': age,
    };
  }
}

4. Parsing JSON to Dart Object

void main() {
  String jsonString = '{"name":"John Doe","email":"john@example.com","age":28}';

  Map<String, dynamic> userMap = jsonDecode(jsonString);
  User user = User.fromJson(userMap);

  print('Name: ${user.name}');
  print('Email: ${user.email}');
  print('Age: ${user.age}');
}

5. Converting Dart Object to JSON String

void convertToJson() {
  User user = User(name: 'Jane Doe', email: 'jane@example.com', age: 25);
  String jsonString = jsonEncode(user.toJson());

  print(jsonString);
}

Working with JSON in Dart allows easy integration with REST APIs, data storage, and state management. For large or complex models, consider using the json_serializable package to generate model code automatically.

By understanding JSON parsing and encoding, Dart developers can confidently build data-driven applications with better structure and scalability.