| name | spring-boot |
| description | Spring Boot Java framework for microservices with auto-configuration. Use for enterprise Java. |
Spring Boot
Java framework for building production-ready microservices.
When to Use
- Enterprise Java applications
- Microservices architecture
- REST APIs with Java/Kotlin
- Cloud-native applications
Quick Start
@RestController
@RequestMapping("/api/users")
public class UserController {
private final UserService userService;
public UserController(UserService userService) {
this.userService = userService;
}
@GetMapping("/{id}")
public ResponseEntity<User> getUser(@PathVariable Long id) {
return userService.findById(id)
.map(ResponseEntity::ok)
.orElse(ResponseEntity.notFound().build());
}
@PostMapping
public ResponseEntity<User> createUser(@Valid @RequestBody CreateUserRequest request) {
User user = userService.create(request);
return ResponseEntity.created(URI.create("/api/users/" + user.getId())).body(user);
}
}
Core Concepts
Dependency Injection
@Service
@Transactional(readOnly = true)
public class UserService {
private final UserRepository repository;
private final PasswordEncoder passwordEncoder;
public UserService(UserRepository repository, PasswordEncoder passwordEncoder) {
this.repository = repository;
this.passwordEncoder = passwordEncoder;
}
@Transactional
public User create(CreateUserRequest request) {
User user = new User();
user.setEmail(request.email());
user.setPassword(passwordEncoder.encode(request.password()));
return repository.save(user);
}
public Optional<User> findById(Long id) {
return repository.findById(id);
}
}
Spring Data JPA
@Entity
@Table(name = "users")
public class User {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
@Column(nullable = false, unique = true)
private String email;
@OneToMany(mappedBy = "author", cascade = CascadeType.ALL)
private List<Post> posts = new ArrayList<>();
}
public interface UserRepository extends JpaRepository<User, Long> {
Optional<User> findByEmail(String email);
@Query("SELECT u FROM User u WHERE u.active = true")
List<User> findActiveUsers();
}
Common Patterns
Exception Handling
@RestControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(ResourceNotFoundException.class)
public ResponseEntity<ErrorResponse> handleNotFound(ResourceNotFoundException ex) {
return ResponseEntity.status(404)
.body(new ErrorResponse(ex.getMessage()));
}
@ExceptionHandler(MethodArgumentNotValidException.class)
public ResponseEntity<ErrorResponse> handleValidation(MethodArgumentNotValidException ex) {
Map<String, String> errors = ex.getBindingResult().getFieldErrors().stream()
.collect(Collectors.toMap(
FieldError::getField,
FieldError::getDefaultMessage
));
return ResponseEntity.badRequest().body(new ErrorResponse("Validation failed", errors));
}
}
Best Practices
Do:
- Use constructor injection
- Use Spring Data repositories
- Implement proper error handling
- Use profiles for environments
Don't:
- Use field injection (@Autowired on fields)
- Expose entities directly
- Skip validation annotations
- Hardcode configuration
Troubleshooting
| Issue | Cause | Solution |
|---|
| Bean not found | Missing @Component | Add stereotype annotation |
| Circular dependency | Constructor circular | Use setter or @Lazy |
| N+1 queries | Missing fetch join | Use @EntityGraph or JOIN FETCH |
References
