How to create a common class in Flutter for managing GET and POST requests using the http package?

I'm working on a Flutter project where I make multiple API calls using the http package. Right now, I'm writing separate get and post methods in different files, which is causing code duplication and inconsistency.

I want to build a single, reusable class that:

Manages a base URL

Handles GET and POST requests

Supports optional headers and JSON encoding

Returns parsed responses

Can be extended easily to support other HTTP methods

Add http dependency to pubspec.yaml

dependencies:
  http: ^0.13.6

2. Create a file: api_service.dart

import 'dart:convert';
import 'package:http/http.dart' as http;

class ApiService {
  final String baseUrl;

  ApiService({required this.baseUrl});

  Future<dynamic> get(String endpoint, {Map<String, String>? headers}) async {
    final url = Uri.parse('$baseUrl$endpoint');
    try {
      final response = await http.get(url, headers: headers);
      return _handleResponse(response);
    } catch (e) {
      throw Exception('GET request error: $e');
    }
  }

  Future<dynamic> post(String endpoint, {Map<String, String>? headers, dynamic body}) async {
    final url = Uri.parse('$baseUrl$endpoint');
    try {
      final response = await http.post(
        url,
        headers: headers ?? {'Content-Type': 'application/json'},
        body: json.encode(body),
      );
      return _handleResponse(response);
    } catch (e) {
      throw Exception('POST request error: $e');
    }
  }

  dynamic _handleResponse(http.Response response) {
    final statusCode = response.statusCode;
    final body = response.body.isNotEmpty ? json.decode(response.body) : null;

    if (statusCode >= 200 && statusCode < 300) {
      return body;
    } else {
      throw Exception('Error ${response.statusCode}: ${response.reasonPhrase}');
    }
  }
}

3. Usage Example:

void main() async {
  final api = ApiService(baseUrl: 'https://jsonplaceholder.typicode.com/');

  // GET request
  try {
    final posts = await api.get('posts');
    print(posts);
  } catch (e) {
    print(e);
  }

  // POST request
  try {
    final newPost = await api.post('posts', body: {
      'title': 'foo',
      'body': 'bar',
      'userId': 1,
    });
    print(newPost);
  } catch (e) {
    print(e);
  }
}