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Module 1: REST Controllers (The Waiter)

📚 Module 1: REST Controllers

Focus: Moving from “Calculations” to “Communication.”

A REST Controller is the front door of your application. It’s where external users (websites, apps) send requests to get data.

🏗️ Step 1: The Controller (The “Waiter”)

In standard Spring Web, we use the @RestController annotation to mark a class as a “Waiter.”

🧩 The Analogy: The Fine Dining Waiter

  1. The Greeting: The user sends a request to a specific URL (The Table).
  2. The Order: The Controller takes the request and decides which “Chef” (Service) should handle it.
  3. The Delivery: The Controller takes the data from the Chef and hands it back to the user in a format they understand (JSON).

In Code:

@RestController
@RequestMapping("/api/products") // The "Section" of the restaurant
public class ProductController {

    @GetMapping // The "Greeting" (READ)
    public List<String> getAllProducts() {
        return List.of("Laptop", "Mouse", "Keyboard");
    }
}

🏗️ Step 2: Mapping (The “Address System”)

How does the internet know which method to call? We use Mapping Annotations.

🧩 The Analogy: The Mall Map

  • @GetMapping: “I want to LOOK at something.” (Read).
  • @PostMapping: “I want to ADD something new.” (Create).
  • @PutMapping: “I want to FIX/REPLACE something.” (Update).
  • @DeleteMapping: “I want to REMOVE something.” (Delete).

🏗️ Step 3: Path Variables (The “Target”)

Sometimes you want to look at one specific item. We use {id} in the URL.

🧩 The Analogy: The Specific Seat

  • URL: /api/products/5
  • “Give me the product sitting in seat number 5.”

In Code:

@GetMapping("/{id}")
public String getProductById(@PathVariable Long id) {
    return "Product Details for ID: " + id;
}

🥅 Module 1 Review

  1. @RestController: The class that handles web requests.
  2. @RequestMapping: The base address for the controller.
  3. HTTP Verbs: GET, POST, PUT, DELETE.
  4. @PathVariable: Getting specific IDs from the URL.