spring-boot-engineer

Spring Boot Engineer

Core Workflow

1. Analyze requirements — Identify service boundaries, APIs, data models, security needs
2. Design architecture — Plan microservices, data access, cloud integration, security; confirm design before coding
3. Implement — Create services with constructor injection and layered architecture (see Quick Start below)
4. Secure — Add Spring Security, OAuth2, method security, CORS configuration; verify security rules compile and pass tests. If compilation or tests fail: review error output, fix the failing rule or configuration, and re-run before proceeding
5. Test — Write unit, integration, and slice tests; run ./mvnw test (or ./gradlew test) and confirm all pass before proceeding. If tests fail: review the stack trace, isolate the failing assertion or component, fix the issue, and re-run the full suite
6. Deploy — Configure health checks and observability via Actuator; validate /actuator/health returns UP. If health is DOWN: check the components detail in the response, resolve the failing component (e.g., datasource, broker), and re-validate

Reference Guide

Load detailed guidance based on context:

Topic	Reference	Load When
Web Layer	references/web.md	Controllers, REST APIs, validation, exception handling
Data Access	references/data.md	Spring Data JPA, repositories, transactions, projections
Security	references/security.md	Spring Security 6, OAuth2, JWT, method security
Cloud Native	references/cloud.md	Spring Cloud, Config, Discovery, Gateway, resilience
Testing	references/testing.md	@SpringBootTest, MockMvc, Testcontainers, test slices

Quick Start — Minimal Working Structure

A standard Spring Boot feature consists of these layers. Use these as copy-paste starting points.

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 or use @Data (Lombok)
}

Repository

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

Service (constructor injection)

@Service
public class ProductService {
    private final ProductRepository repo;

    public ProductService(ProductRepository repo) { // constructor injection — no @Autowired
        this.repo = repo;
    }

    @Transactional(readOnly = true)
    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, FieldError::getDefaultMessage));
    }

    @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"); product.setPrice(BigDecimal.TEN);
        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"));
    }
}

Constraints

MUST DO

Rule	Correct Pattern
Constructor injection	public MyService(Dep dep) { this.dep = dep; }
Validate API input	@Valid @RequestBody MyRequest req on every mutating endpoint
Type-safe config	@ConfigurationProperties(prefix = "app") bound to a record/class
Appropriate stereotype	@Service for business logic, @Repository for data, @RestController for HTTP
Transaction scope	@Transactional on multi-step writes; @Transactional(readOnly = true) on reads
Hide internals	Catch domain exceptions in @RestControllerAdvice; return problem details, not stack traces
Externalize secrets	Use environment variables or Spring Cloud Config — never application.properties

MUST NOT DO

• Use field injection (@Autowired on fields)
• Skip input validation on API endpoints
• Use @Component when @Service/@Repository/@Controller applies
• Mix blocking and reactive code (e.g., calling .block() inside a WebFlux chain)
• Store secrets or credentials in application.properties/application.yml
• Hardcode URLs, credentials, or environment-specific values
• Use deprecated Spring Boot 2.x patterns (e.g., WebSecurityConfigurerAdapter)