spring-boot

# Spring Boot Expert ## What I Do - Build REST APIs with Spring Web and Spring Data - Configure Spring Security for authentication and authorization - Implement reactive programming with WebFlux - Set up Spring Data JPA with proper entity design - Configure microservices with Spring Cloud ## When to Use Me - Creating Spring Boot applications - Designing RESTful APIs - Implementing security with Spring Security - Setting up database access with Spring Data - Building microservices architectures ## Key Principles 1. **Constructor Injection**: Always prefer constructor over field injection 2. **DTO Pattern**: Never expose entities directly in API responses 3. **Exception Handling**: Use @ControllerAdvice for centralized error handling 4. **Validation**: Use Bean Validation (@Valid) at API boundaries 5. **Profiles**: Use application profiles for environment-specific config ## Common Patterns ### REST Controller ```java @RestController @RequestMapping("/api/users") @RequiredArgsConstructor public class UserController { private final UserService userService; @GetMapping("/{id}") public ResponseEntity<UserDto> getUser(@PathVariable Long id) { return userService.findById(id) .map(ResponseEntity::ok) .orElse(ResponseEntity.notFound().build()); } @PostMapping @ResponseStatus(HttpStatus.CREATED) public UserDto createUser(@Valid @RequestBody CreateUserRequest request) { return userService.create(request); } } ``` ### Global Exception Handler ```java @RestControllerAdvice public class GlobalExceptionHandler { @ExceptionHandler(EntityNotFoundException.class) public ResponseEntity<ErrorResponse> handleNotFound(EntityNotFoundException ex) { return ResponseEntity.status(HttpStatus.NOT_FOUND) .body(new ErrorResponse(ex.getMessage())); } } ``` ## Validation ```bash ./mvnw test ./mvnw spring-boot:run ```