Spring Boot Skill

Enterprise Spring Boot 3.x development with focus on clean architecture and production-ready code.

Core Workflow

1. Analyze - Understand requirements, identify service boundaries, APIs, data models
2. Design - Plan architecture, confirm design before coding
3. Implement - Build with constructor injection and layered architecture
4. Secure - Add Spring Security, OAuth2, method security; verify tests pass
5. Test - Write unit, integration tests; run ./mvnw test and confirm all pass
6. Deploy - Configure health checks via Actuator; validate /actuator/health returns UP

Quick Start Templates

Entity

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

    @NotBlank
    private String name;

    @DecimalMin("0.0")
    private BigDecimal price;

    // Getters/Setters (no Lombok)
}

Repository

public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findByNameContainingIgnoreCase(String name);
}

Service

@Service
@Transactional(readOnly = true)
public class ProductService {
    private final ProductRepository repo;

    public ProductService(ProductRepository repo) {
        this.repo = repo;
    }

    public List<Product> search(String name) {
        return repo.findByNameContainingIgnoreCase(name);
    }

    @Transactional
    public Product create(ProductRequest request) {
        var product = new Product();
        product.setName(request.name());
        product.setPrice(request.price());
        return repo.save(product);
    }
}

REST Controller

@RestController
@RequestMapping("/api/v1/products")
@Validated
public class ProductController {
    private final ProductService service;

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

    @GetMapping
    public List<Product> search(@RequestParam(defaultValue = "") String name) {
        return service.search(name);
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public Product create(@Valid @RequestBody ProductRequest request) {
        return service.create(request);
    }
}

DTO (Record)

public record ProductRequest(
    @NotBlank String name,
    @DecimalMin("0.0") BigDecimal price
) {}

Global Exception Handler

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(MethodArgumentNotValidException.class)
    @ResponseStatus(HttpStatus.BAD_REQUEST)
    public Map<String, String> handleValidation(MethodArgumentNotValidException ex) {
        return ex.getBindingResult().getFieldErrors().stream()
            .collect(Collectors.toMap(FieldError::getField,
                    error -> error.getDefaultMessage() != null ? error.getDefaultMessage() : "Invalid"));
    }

    @ExceptionHandler(EntityNotFoundException.class)
    @ResponseStatus(HttpStatus.NOT_FOUND)
    public Map<String, String> handleNotFound(EntityNotFoundException ex) {
        return Map.of("error", ex.getMessage());
    }
}

Test Slice

@WebMvcTest(ProductController.class)
class ProductControllerTest {
    @Autowired MockMvc mockMvc;
    @MockBean ProductService service;

    @Test
    void createProduct_validRequest_returns201() throws Exception {
        var product = new Product();
        product.setName("Widget");
        when(service.create(any())).thenReturn(product);

        mockMvc.perform(post("/api/v1/products")
                .contentType(MediaType.APPLICATION_JSON)
                .content("""{"name":"Widget","price":10.0}"""))
            .andExpect(status().isCreated())
            .andExpect(jsonPath("$.name").value("Widget"));
    }
}

Reference Guide

Load detailed patterns based on context:

Constraints

MUST DO

• Constructor injection (no field injection)
• @Valid on all request bodies
• @Transactional for multi-step writes
• @Transactional(readOnly = true) for reads
• Type-safe config with @ConfigurationProperties
• Global exception handling with @RestControllerAdvice
• Externalize secrets (use env vars, not properties files)

MUST NOT DO

• Field injection (@Autowired on fields)
• Skip input validation on endpoints
• Mix blocking and reactive code
• Store secrets in application.properties
• Use deprecated Spring Boot 2.x patterns
• Hardcode URLs, credentials, environment values

Architecture Patterns

Project Structure:

src/main/java/pl/piomin/services/
├── controller/     # REST endpoints
├── service/        # Business logic
├── repository/     # Data access
├── model/          # Entities
├── dto/            # Request/Response DTOs
├── config/         # Configuration
└── exception/      # Custom exceptions + handler

Layering:

• Controller → Service → Repository
• Controller handles HTTP, validation
• Service handles business logic, transactions
• Repository handles data persistence

Clean Architecture Principles:

• Domain models independent of frameworks
• Use case driven design
• Dependency inversion (interfaces)
• Clear boundaries between layers

Common Annotations

Reactive WebFlux Endpoint

@RestController
@RequestMapping("/api/v1/orders")
public class OrderController {
    private final OrderService orderService;

    public OrderController(OrderService orderService) {
        this.orderService = orderService;
    }

    @GetMapping("/{id}")
    public Mono<ResponseEntity<OrderDto>> getOrder(@PathVariable UUID id) {
        return orderService.findById(id)
                .map(ResponseEntity::ok)
                .defaultIfEmpty(ResponseEntity.notFound().build());
    }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public Mono<OrderDto> createOrder(@Valid @RequestBody CreateOrderRequest request) {
        return orderService.create(request);
    }
}

Spring Security JWT

@Configuration
@EnableMethodSecurity
public class SecurityConfig {
    @Bean
    public SecurityFilterChain filterChain(HttpSecurity http) throws Exception {
        return http
                .csrf(AbstractHttpConfigurer::disable)
                .sessionManagement(s -> s.sessionCreationPolicy(STATELESS))
                .authorizeHttpRequests(auth -> auth
                        .requestMatchers("/actuator/health").permitAll()
                        .anyRequest().authenticated())
                .oauth2ResourceServer(oauth2 -> oauth2.jwt(Customizer.withDefaults()))
                .build();
    }
}

Knowledge Base

Spring Boot 3.x, Java 21, Spring WebFlux, Project Reactor, Spring Data JPA, Spring Security 6, OAuth2/JWT, Hibernate, R2DBC, Spring Cloud, Resilience4j, Micrometer, JUnit 5, TestContainers, Mockito, Maven/Gradle