spring-boot-expert

Spring Boot Expert

Expert guidance for Spring Boot development, Spring Framework, building REST APIs, and microservices architecture.

Core Concepts

Spring Boot Fundamentals

• Auto-configuration
• Dependency injection
• Spring Boot Starters
• Application properties
• Profiles and configuration
• Spring Boot Actuator

Spring Framework

• Spring Core (IoC, DI)
• Spring Data JPA
• Spring Security
• Spring Web MVC
• Spring AOP
• Spring Transaction Management

Microservices

• Service discovery
• API Gateway
• Circuit breakers
• Distributed tracing
• Configuration management

Spring Boot Application

// Main application class
@SpringBootApplication
@EnableJpaAuditing
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

// Entity with JPA
@Entity
@Table(name = "users")
@EntityListeners(AuditingEntityListener.class)
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, unique = true)
    private String email;

    @Column(nullable = false)
    private String password;

    @CreatedDate
    @Column(nullable = false, updatable = false)
    private LocalDateTime createdAt;

    @LastModifiedDate
    private LocalDateTime updatedAt;

    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL)
    private List<Post> posts = new ArrayList<>();

    // Getters and setters
}

@Entity
@Table(name = "posts")
public class Post {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String title;

    @Column(columnDefinition = "TEXT")
    private String content;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "user_id", nullable = false)
    private User author;

    @CreatedDate
    private LocalDateTime createdAt;

    // Getters and setters
}

REST API Controller

@RestController
@RequestMapping("/api/users")
@RequiredArgsConstructor
public class UserController {

    private final UserService userService;

    @GetMapping
    public ResponseEntity<Page<UserDto>> getUsers(
            @RequestParam(defaultValue = "0") int page,
            @RequestParam(defaultValue = "20") int size,
            @RequestParam(defaultValue = "id") String sortBy,
            @RequestParam(defaultValue = "ASC") Sort.Direction direction
    ) {
        Pageable pageable = PageRequest.of(page, size, Sort.by(direction, sortBy));
        Page<UserDto> users = userService.findAll(pageable);
        return ResponseEntity.ok(users);
    }

    @GetMapping("/{id}")
    public ResponseEntity<UserDto> getUser(@PathVariable Long id) {
        return userService.findById(id)
                .map(ResponseEntity::ok)
                .orElse(ResponseEntity.notFound().build());
    }

    @PostMapping
    public ResponseEntity<UserDto> createUser(
            @Valid @RequestBody UserCreateDto userDto
    ) {
        UserDto created = userService.create(userDto);
        URI location = ServletUriComponentsBuilder
                .fromCurrentRequest()
                .path("/{id}")
                .buildAndExpand(created.getId())
                .toUri();

        return ResponseEntity.created(location).body(created);
    }

    @PutMapping("/{id}")
    public ResponseEntity<UserDto> updateUser(
            @PathVariable Long id,
            @Valid @RequestBody UserUpdateDto userDto
    ) {
        return userService.update(id, userDto)
                .map(ResponseEntity::ok)
                .orElse(ResponseEntity.notFound().build());
    }

    @DeleteMapping("/{id}")
    public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
        if (userService.delete(id)) {
            return ResponseEntity.noContent().build();
        }
        return ResponseEntity.notFound().build();
    }
}

// DTOs with validation
public record UserDto(
        Long id,
        String email,
        LocalDateTime createdAt
) {}

public record UserCreateDto(
        @NotBlank @Email String email,
        @NotBlank @Size(min = 8) String password
) {}

public record UserUpdateDto(
        @Email String email
) {}