Simple way to dynamically convert from and to JSON using build-time generators given a type.

Note: Ignore the warning and tags indicating that this package is no compatible with the Flutter and other SDKs. This is reported because this generator package uses dart:mirrors library which is not supported by those SDKs. In this case, it will all work fine as this package is supposed to be just build-time generators. This package should ONLY be added under dev_dependencies to work correctly. The supporting simple_json_mapper package also needs to be included but as a regular dependency under dependencies.


  1. A single mapper.g.dart is generated at build-time when the build_runner build command is executed. View example of generated file. Advanced example
  2. This generated file contains the necessary code (serialization and de-serialization logic) to map from and to JSON.
  3. These object mappers are registered with the JSON Mapper in the init function.
  4. The init function is the first line of code that should be executed in your main.dart file.
  5. At runtime, all of the mappers are registered (using the aforementioned init method) and can then be looked up using the class type parameter passed into the serialize<T> or deserialize<T> generic methods.


  • Simple
  • No messy .g.dart files for each serializable file (single root-level file which contains all of the generated code)
  • Dynamic serialization and de-serialization without using the actual type directly while still maintaining type-safety. i.e. JsonMapper.serialize(account) vs account.toJson() (account does not need to have any logic and it is not used directly for the actual serialization)
  • Model files stay clean (no extra generated code) and don't care about the serialization logic (SRP)
  • No need to specify custom object and iterable type casting
  • No bloated reflection on the entire type with linting/analyzer issues

Dynamic serialization and de-serialization allows for allow for creating great type-safe APIs. A good example is a simple storage service in flutter.

class StorageService implements IStorageService {
  const StorageService(this.preferences);
  final SharedPreferences preferences;

  Future<T> get<T>({T Function() defaultFn, bool private = false}) async {
    return getWithKey(T.toString(), defaultFn: defaultFn, private: private);

  Future<T> getWithKey<T>(String key,
      {T Function() defaultFn, bool private = false}) async {
    return JsonMapper.deserialize<T>(
            await getProvider(private).getString(key)) ??

  Future<bool> set<T>(T value, [bool private = false]) {
    return setWithKey(T.toString(), value, private);

  Future<bool> setWithKey<T>(String key, T value, [bool private = false]) {
    return getProvider(private).setString(key, JsonMapper.serialize(value));

  IStorageProvider getProvider(bool private) {
    return private && !AppUtils.isWeb
        ? SecureStorage()
        : SharedPreferencesStorage(preferences);

Using simple_json, this StorageService has a simple generic type-safe API that can store serialize the models classes before storing them as string making it really simple and boilerplate-free.

Quick Start

pubspec.yaml (Note: simple_json must be added under dev_dependencies)

  simple_json_mapper: ^2.2.0

  simple_json: ^2.2.0
  build_runner: ^1.10.0



// Generated file. Can be added to .gitignore
import 'mapper.g.dart' as mapper;

void main() {



import 'package:simple_json_mapper/simple_json_mapper.dart';

// Required annotation/decorator to opt-in model for json setup. Alias for [JsonObject]
class Account {
  const Account({
  // Specify the enum serialization type (index or value based). Alias for [JsonEnumProperty]
  // SerializationType.Index: Savings = 0, Checking = 1
  // SerializationType.Value: Savings = 'Savings', Checking = 'Checking'
  // Enum fields can be annotated with [EnumValue] to provide a custom value.
  @JEnumProp(serializationType: SerializationType.Index)
  final AccountType type;
  final String name;
  final String number;
  final double amount;

  @JsonProperty(name: 'tranCount', defaultValue: 11)
  final int transactionCount;

  final bool isActive;

  // Alias for [JsonProperty]
  @JProp(ignore: true)
  final String localText;

  final Product product;

class Product {
  const Product({, this.expiry, this.sizes, this.tests});
  final String name;
  final DateTime expiry;
  final List<int> sizes;
  final List<Test> tests;

// Linked models don't require the annotation but it is recommended.
class Test {
  const Test({});
  final String name;

enum AccountType {
  // Override serialization enum value
  @EnumValue(value: 25)
  @EnumValue(value: 10)


  final product = Product(
    name: 'Test',
    sizes: [10, 20, 40],
    tests: [
      Test(name: 'hello'),
      Test(name: 'blah'),
  final account = Account(
    type: AccountType.Checking,
    name: 'Test',
    number: 'xxx12414',
    amount: 100.50,
    transactionCount: 10,
    isActive: true,
    product: product,
    localText: 'ignored text',
  final accountJson = JsonMapper.serialize(account);


  final account = JsonMapper.deserialize<Account>(accountJson);


  // Convert all deserialized strings to lowercase and all serialized strings to uppercase.
    JsonConverter<String, String>.fromFunction(
      fromJson: (value) => value.toLowerCase(),
      toJson: (value) => value.toUpperCase(),

  // Converter for transforming all DateTime string values to a special format defined by the given class.

Custom JsonMapper

  // Custom mapper that has it own set of converters. Useful for encapsulating for special, adhoc serializations
  // e.g. SQLite
  final customMapper = CustomJsonMapper(
    converters: [
      // Converter for changing all boolean values from boolean to int and vice versa on serialization.
      JsonConverter<int, bool>.fromFunction(
        fromJson: (value) => value == 1 ? true : false,
        toJson: (value) => value ? 1 : 0,
  // Note the usage of [customerMapper] here.

Refer to the advanced example for advanced usage of functionalities.

Generating Mapper File


# dart
pub get
pub run build_runner build
# flutter
flutter pub get
flutter packages pub run build_runner build


# dart
pub get
pub run build_runner watch
# flutter
flutter pub get
flutter packages pub run build_runner watch