Java Spring Boot cơ bản: REST API đầu tiên

🎯 Spring Boot là gì?

Spring Boot là framework giúp xây dựng ứng dụng Java nhanh chóng với:

• Auto-configuration
• Embedded server (Tomcat)
• Production-ready features

1. Setup Project

Bước 1: Generate project

Vào start.spring.io:

• Project: Maven
• Language: Java
• Spring Boot: 3.2.x
• Dependencies: Spring Web, Spring Data JPA, PostgreSQL Driver

Bước 2: Cấu trúc project

src/main/java/com/example/demo
├── DemoApplication.java       # Main class
├── controller/                # REST Controllers
├── service/                   # Business Logic
├── repository/                # Database Access
└── model/                     # Entity classes

src/main/resources
├── application.properties     # Config
└── application.yml           # Config (alternative)

2. Tạo Entity

// model/User.java
@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    
    @Column(nullable = false)
    private String name;
    
    @Column(unique = true, nullable = false)
    private String email;
    
    // Getters, Setters, Constructors
}

3. Tạo Repository

// repository/UserRepository.java
@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findByEmail(String email);
    List<User> findByNameContaining(String keyword);
}

Giải thích:

• Kế thừa JpaRepository → Có sẵn CRUD methods
• Không cần implement, Spring tự generate!

4. Tạo Service Layer

// service/UserService.java
@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;
    
    public List<User> getAllUsers() {
        return userRepository.findAll();
    }
    
    public User getUserById(Long id) {
        return userRepository.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("User not found"));
    }
    
    public User createUser(User user) {
        return userRepository.save(user);
    }
    
    public User updateUser(Long id, User userDetails) {
        User user = getUserById(id);
        user.setName(userDetails.getName());
        user.setEmail(userDetails.getEmail());
        return userRepository.save(user);
    }
    
    public void deleteUser(Long id) {
        User user = getUserById(id);
        userRepository.delete(user);
    }
}

5. Tạo REST Controller

// controller/UserController.java
@RestController
@RequestMapping("/api/users")
public class UserController {
    @Autowired
    private UserService userService;
    
    // GET /api/users
    @GetMapping
    public List<User> getAllUsers() {
        return userService.getAllUsers();
    }
    
    // GET /api/users/1
    @GetMapping("/{id}")
    public ResponseEntity<User> getUserById(@PathVariable Long id) {
        User user = userService.getUserById(id);
        return ResponseEntity.ok(user);
    }
    
    // POST /api/users
    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody User user) {
        User created = userService.createUser(user);
        return ResponseEntity.status(HttpStatus.CREATED).body(created);
    }
    
    // PUT /api/users/1
    @PutMapping("/{id}")
    public ResponseEntity<User> updateUser(
        @PathVariable Long id,
        @RequestBody User user
    ) {
        User updated = userService.updateUser(id, user);
        return ResponseEntity.ok(updated);
    }
    
    // DELETE /api/users/1
    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
        userService.deleteUser(id);
        return ResponseEntity.noContent().build();
    }
}

6. Configuration

application.properties

# Database
spring.datasource.url=jdbc:postgresql://localhost:5432/mydb
spring.datasource.username=postgres
spring.datasource.password=password

# JPA
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

# Server
server.port=8080

7. Exception Handling

// exception/ResourceNotFoundException.java
public class ResourceNotFoundException extends RuntimeException {
    public ResourceNotFoundException(String message) {
        super(message);
    }
}

// exception/GlobalExceptionHandler.java
@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleNotFound(
        ResourceNotFoundException ex
    ) {
        ErrorResponse error = new ErrorResponse(
            HttpStatus.NOT_FOUND.value(),
            ex.getMessage(),
            LocalDateTime.now()
        );
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(error);
    }
}

8. Testing với Postman

GET All Users

GET http://localhost:8080/api/users

POST Create User

POST http://localhost:8080/api/users
Content-Type: application/json

{
  "name": "Ngọc Hân",
  "email": "han@example.com"
}

PUT Update User

PUT http://localhost:8080/api/users/1
Content-Type: application/json

{
  "name": "Updated Name",
  "email": "newemail@example.com"
}

9. Best Practices

DTO Pattern

// dto/UserDTO.java
public class UserDTO {
    private Long id;
    private String name;
    private String email;
    // No sensitive fields like password!
}

// mapper/UserMapper.java
@Component
public class UserMapper {
    public UserDTO toDTO(User user) {
        return new UserDTO(user.getId(), user.getName(), user.getEmail());
    }
}

Validation

@Entity
public class User {
    @NotBlank(message = "Name is required")
    private String name;
    
    @Email(message = "Invalid email format")
    @NotBlank(message = "Email is required")
    private String email;
}

// Controller
@PostMapping
public ResponseEntity<User> createUser(@Valid @RequestBody User user) {
    // If validation fails, return 400 Bad Request
}

10. Kết luận

Bạn đã học:

• ✅ Setup Spring Boot project
• ✅ Entity, Repository, Service, Controller
• ✅ REST API với CRUD operations
• ✅ Exception handling
• ✅ Database configuration

Next steps:

• Học Spring Security (authentication)
• Implement pagination & sorting
• Write unit tests với JUnit & Mockito
• Deploy lên Heroku/Railway