---
name: flutter-handling-http-and-json-a748776a2a73
description: "Executes HTTP requests and handles JSON serialization in a Flutter app. Use when integrating with REST APIs or parsing structured data from external sources."
metadata:
  model: "models/gemini-3.1-pro-preview"
  last_modified: "Thu, 12 Mar 2026 22:18:44 GMT"

---
# Handling HTTP and JSON

## Contents
- [Core Guidelines](#core-guidelines)
- [Workflow: Executing HTTP Operations](#workflow-executing-http-operations)
- [Workflow: Implementing JSON Serialization](#workflow-implementing-json-serialization)
- [Workflow: Parsing Large JSON in the Background](#workflow-parsing-large-json-in-the-background)
- [Examples](#examples)

## Core Guidelines

- **Enforce HTTPS:** iOS and Android disable cleartext (HTTP) connections by default. Always use HTTPS endpoints. If HTTP is strictly required for debugging, configure `network_security_config.xml` (Android) and `NSAppTransportSecurity` (iOS).
- **Construct URIs Safely:** Always use `Uri.https(authority, unencodedPath, [queryParameters])` to safely build URLs. This handles encoding and formatting reliably, preventing string concatenation errors.
- **Handle Status Codes:** Always validate the `http.Response.statusCode`. Treat `200` (OK) and `201` (Created) as success. Throw explicit exceptions for other codes (do not return `null`).
- **Prevent UI Jank:** Move expensive JSON parsing operations (taking >16ms) to a background isolate using the `compute()` function.
- **Structured AI Output:** When integrating LLMs, enforce reliable JSON output by specifying a strict JSON schema in the system prompt and setting the response MIME type to `application/json`.

## Workflow: Executing HTTP Operations

Use this workflow to implement network requests using the `http` package.

**Task Progress:**
- [ ] Add the `http` package to `pubspec.yaml`.
- [ ] Configure platform permissions (Internet permission in `AndroidManifest.xml` and macOS `.entitlements`).
- [ ] Construct the target `Uri`.
- [ ] Execute the HTTP method.
- [ ] Validate the response and parse the JSON payload.

**Conditional Implementation:**
- **If fetching data (GET):** Use `http.get(uri)`.
- **If sending new data (POST):** Use `http.post(uri, headers: {...}, body: jsonEncode(data))`. Ensure `Content-Type` is `application/json; charset=UTF-8`.
- **If updating data (PUT):** Use `http.put(uri, headers: {...}, body: jsonEncode(data))`.
- **If deleting data (DELETE):** Use `http.delete(uri, headers: {...})`.

**Feedback Loop: Validation & Error Handling**
1. Run the HTTP request.
2. Check `response.statusCode`.
3. If `200` or `201`, call `jsonDecode(response.body)` and map to a Dart object.
4. If any other code, throw an `Exception('Failed to load/update/delete resource')`.
5. Review errors -> fix endpoint, headers, or payload structure.

## Workflow: Implementing JSON Serialization

Choose the serialization strategy based on project complexity.

**Conditional Implementation:**
- **If building a small prototype or simple models:** Use manual serialization with `dart:convert`.
- **If building a production app with complex/nested models:** Use code generation with `json_serializable`.

### Manual Serialization Setup
**Task Progress:**
- [ ] Import `dart:convert`.
- [ ] Define the Model class with `final` properties.
- [ ] Implement a `factory Model.fromJson(Map<String, dynamic> json)` constructor.
- [ ] Implement a `Map<String, dynamic> toJson()` method.

### Code Generation Setup (`json_serializable`)
**Task Progress:**
- [ ] Add dependencies: `flutter pub add json_annotation` and `flutter pub add -d build_runner json_serializable`.
- [ ] Import `json_annotation.dart` in the model file.
- [ ] Add the `part 'model_name.g.dart';` directive.
- [ ] Annotate the class with `@JsonSerializable()`. Use `explicitToJson: true` if the class contains nested models.
- [ ] Define the `fromJson` factory and `toJson` method delegating to the generated functions.
- [ ] Run the generator: `dart run build_runner build --delete-conflicting-outputs`.

## Workflow: Parsing Large JSON in the Background

Use this workflow to prevent frame drops when parsing large JSON payloads (e.g., lists of 1000+ items).

**Task Progress:**
- [ ] Create a top-level or static function that takes a `String` (the response body) and returns the parsed Dart object (e.g., `List<Model>`).
- [ ] Inside the function, call `jsonDecode` and map the results to the Model class.
- [ ] In the HTTP fetch method, pass the top-level parsing function and the `response.body` to Flutter's `compute()` function.

## Examples

### Example 1: HTTP GET with Manual Serialization
```dart
import 'dart:convert';
import 'package:http/http.dart' as http;

class Album {
  final int id;
  final String title;

  const Album({required this.id, required this.title});

  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      id: json['id'] as int,
      title: json['title'] as String,
    );
  }
}

Future<Album> fetchAlbum() async {
  final uri = Uri.https('jsonplaceholder.typicode.com', '/albums/1');
  final response = await http.get(uri);

  if (response.statusCode == 200) {
    return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
  } else {
    throw Exception('Failed to load album');
  }
}
```

### Example 2: HTTP POST Request
```dart
Future<Album> createAlbum(String title) async {
  final uri = Uri.https('jsonplaceholder.typicode.com', '/albums');
  final response = await http.post(
    uri,
    headers: <String, String>{
      'Content-Type': 'application/json; charset=UTF-8',
    },
    body: jsonEncode(<String, String>{'title': title}),
  );

  if (response.statusCode == 201) {
    return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
  } else {
    throw Exception('Failed to create album.');
  }
}
```

### Example 3: Background Parsing with `compute`
```dart
import 'dart:convert';
import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;

// 1. Top-level function for parsing
List<Photo> parsePhotos(String responseBody) {
  final parsed = (jsonDecode(responseBody) as List<Object?>)
      .cast<Map<String, Object?>>();
  return parsed.map<Photo>(Photo.fromJson).toList();
}

// 2. Fetch function using compute
Future<List<Photo>> fetchPhotos(http.Client client) async {
  final uri = Uri.https('jsonplaceholder.typicode.com', '/photos');
  final response = await client.get(uri);

  if (response.statusCode == 200) {
    // Run parsePhotos in a separate isolate
    return compute(parsePhotos, response.body);
  } else {
    throw Exception('Failed to load photos');
  }
}
```

### Example 4: Code Generation (`json_serializable`)
```dart
import 'package:json_annotation/json_annotation.dart';

part 'user.g.dart';

@JsonSerializable(explicitToJson: true)
class User {
  final String name;
  
  @JsonKey(name: 'registration_date_millis')
  final int registrationDateMillis;

  User(this.name, this.registrationDateMillis);

  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
  Map<String, dynamic> toJson() => _$UserToJson(this);
}
```


---
Source attribution: dangdungvn
Original project: https://github.com/dangdungvn/review_system_app/blob/f397d2abe0a8d4c041cd274f0ffc5680d85e7c44/.github/skills/flutter-handling-http-and-json/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2024 Minh Nguyen

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: dangdungvn
Original project: https://github.com/dangdungvn/review_system_app/blob/f397d2abe0a8d4c041cd274f0ffc5680d85e7c44/.github/skills/flutter-handling-http-and-json/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Mobile Developer, Product Manager
Specialties: API, Mobile
Tools: Http
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: b686ff3b4a95e4db50672663908839991d493d55d5fb0b914585043af1b31e92