REST API Complete Guide 🌐

Backend Communication System

1. What is REST API?

REST API is a way for frontend apps (React, Android, Flutter) to communicate with backend servers using HTTP requests.

2. HTTP Methods

GET    → Read data
POST   → Create data
PUT    → Update data
DELETE → Remove data

3. Example API

GET https://api.example.com/users
POST https://api.example.com/login

4. Node.js REST API

const express = require('express');
const app = express();

app.use(express.json());

app.get('/users', (req, res) => {
    res.json([{ name: "Sasank" }]);
});

app.post('/login', (req, res) => {
    res.json({ message: "Login Success" });
});

app.listen(3000);

5. Frontend API Call (JavaScript)

fetch("https://api.example.com/users")
  .then(res => res.json())
  .then(data => console.log(data));

6. React API Example

useEffect(() => {
  fetch("/api/users")
    .then(res => res.json())
    .then(data => setUsers(data));
}, []);

7. Android API (Kotlin)

Retrofit:
- Used for API calls
- Convert JSON → Kotlin objects

8. Flutter API Example

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

var response = await http.get(Uri.parse("https://api.com/users"));
print(response.body);

9. How REST API Works

Frontend → sends request
Backend  → processes data
Database → stores data
Response → returns JSON

10. JSON Format

{
  "name": "Sasank",
  "role": "Developer"
}

11. Real Projects