Building REST APIs with Spring MVC [Java Spring Boot Mastery Series – Part 3]

🎯 Objective

In this section, you will learn how to:

• Create RESTful APIs
• Handle requests and responses
• Use HTTP methods correctly
• Return proper HTTP status codes

🔧 Step 1: Create a Model Class

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private Double price;

    // Getters and Setters
}

🔍 Explanation

• @Entity: Marks this class as a JPA entity.
• @Id: Primary key field.
• @GeneratedValue: Auto-generates ID.
• name, price: Fields mapped to database columns

📦 Step 2: Create a Repository

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
}

🔍 Explanation

• Extends JpaRepository<Product, Long> to get built-in CRUD methods.
• No need for implementation — Spring Data provides it at runtime.

🧠 Step 3: Create a Service Layer

@Service
public class ProductService {

    @Autowired
    private ProductRepository productRepository;

    public List<Product> getAll() {
        return productRepository.findAll();
    }

    public Product getById(Long id) {
        return productRepository.findById(id)
                .orElseThrow(() -> new ResourceNotFoundException("Product not found: " + id));
    }

    public Product save(Product product) {
        return productRepository.save(product);
    }

    public void delete(Long id) {
        productRepository.deleteById(id);
    }
}

🔍 Explanation

• Encapsulates business logic.
• findAll(), save(), findById(), deleteById() are provided by Spring Data.
• Custom ResourceNotFoundException helps handle 404s.

🌐 Step 4: Create a REST Controller

@RestController
@RequestMapping("/api/products")
public class ProductController {

    private final ProductService productService;

    public ProductController(ProductService productService) {
        this.productService = productService;
    }

    @GetMapping
    public List<Product> getAllProducts() {
        return productService.getAll();
    }

    @GetMapping("/{id}")
    public ResponseEntity<Product> getProductById(@PathVariable Long id) {
        return ResponseEntity.ok(productService.getById(id));
    }

    @PostMapping
    public ResponseEntity<Product> createProduct(@RequestBody Product product) {
        return new ResponseEntity<>(productService.save(product), HttpStatus.CREATED);
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteProduct(@PathVariable Long id) {
        productService.delete(id);
        return ResponseEntity.noContent().build();
    }
}

🔍 Explanation

• @RestController: Marks the class for REST API responses.
• @RequestMapping("/api/products"): Base URL path for the controller.
• @GetMapping, @PostMapping, @DeleteMapping: Maps HTTP methods to controller actions.
• @PathVariable: Binds URL segment to method param.
• @RequestBody: Maps JSON to Java object.
• ResponseEntity: Builds a response with a status code.

🚫 Optional: Custom Exception Handling

@ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}

🔍 Explanation

• Custom exception class to return HTTP 404 when data not found.
• Annotated with @ResponseStatus(HttpStatus.NOT_FOUND).

📬 Test the API using Postman

• GET: http://localhost:8080/api/products
• GET by ID: http://localhost:8080/api/products/1
• POST: http://localhost:8080/api/products

{
  "name": "Laptop",
  "price": 55000.0
}

• DELETE: http://localhost:8080/api/products/1

✅ You’ve now built a fully functional RESTful API with CRUD operations using Spring Boot MVC architecture!

➡️ Next Up: Part 4 – Data Validation and Exception Handling