springboot-patterns

SKILL.md

Spring Boot Development Patterns

Spring Boot architecture and API patterns for scalable, production-grade services.

When to Activate

Building REST APIs with Spring MVC or WebFlux

Structuring controller → service → repository layers

Configuring Spring Data JPA, caching, or async processing

Adding validation, exception handling, or pagination

Setting up profiles for dev/staging/production environments

Implementing event-driven patterns with Spring Events or Kafka

REST API Structure
@RestController
@RequestMapping("/api/markets")
@Validated
class MarketController {
  private final MarketService marketService;

  MarketController(MarketService marketService) {
    this.marketService = marketService;
  }

  @GetMapping
  ResponseEntity<Page<MarketResponse>> list(
      @RequestParam(defaultValue = "0") int page,
      @RequestParam(defaultValue = "20") int size) {
    Page<Market> markets = marketService.list(PageRequest.of(page, size));
    return ResponseEntity.ok(markets.map(MarketResponse::from));
  }

  @PostMapping
  ResponseEntity<MarketResponse> create(@Valid @RequestBody CreateMarketRequest request) {
    Market market = marketService.create(request);
    return ResponseEntity.status(HttpStatus.CREATED).body(MarketResponse.from(market));
  }
}

Repository Pattern (Spring Data JPA)

public interface MarketRepository extends JpaRepository<MarketEntity, Long> {
  @Query("select m from MarketEntity m where m.status = :status order by m.volume desc")
  List<MarketEntity> findActive(@Param("status") MarketStatus status, Pageable pageable);
}

Service Layer with Transactions

@Service
public class MarketService {
  private final MarketRepository repo;

  public MarketService(MarketRepository repo) {
    this.repo = repo;
  }

  @Transactional
  public Market create(CreateMarketRequest request) {
    MarketEntity entity = MarketEntity.from(request);
    MarketEntity saved = repo.save(entity);
    return Market.from(saved);
  }
}

DTOs and Validation

public record CreateMarketRequest(
    @NotBlank @Size(max = 200) String name,
    @NotBlank @Size(max = 2000) String description,
    @NotNull @FutureOrPresent Instant endDate,
    @NotEmpty List<@NotBlank String> categories) {}

public record MarketResponse(Long id, String name, MarketStatus status) {
  static MarketResponse from(Market market) {
    return new MarketResponse(market.id(), market.name(), market.status());
  }
}

Exception Handling

@ControllerAdvice
class GlobalExceptionHandler {
  @ExceptionHandler(MethodArgumentNotValidException.class)
  ResponseEntity<ApiError> handleValidation(MethodArgumentNotValidException ex) {
    String message = ex.getBindingResult().getFieldErrors().stream()
        .map(e -> e.getField() + ": " + e.getDefaultMessage())
        .collect(Collectors.joining(", "));
    return ResponseEntity.badRequest().body(ApiError.validation(message));
  }

  @ExceptionHandler(AccessDeniedException.class)
  ResponseEntity<ApiError> handleAccessDenied() {
    return ResponseEntity.status(HttpStatus.FORBIDDEN).body(ApiError.of("Forbidden"));
  }

  @ExceptionHandler(Exception.class)
  ResponseEntity<ApiError> handleGeneric(Exception ex) {
    // Log unexpected errors with stack traces
    return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
        .body(ApiError.of("Internal server error"));
  }
}

Caching

Requires @EnableCaching on a configuration class.

@Service
public class MarketCacheService {
  private final MarketRepository repo;

  public MarketCacheService(MarketRepository repo) {
    this.repo = repo;
  }

  @Cacheable(value = "market", key = "#id")
  public Market getById(Long id) {
    return repo.findById(id)
        .map(Market::from)
        .orElseThrow(() -> new EntityNotFoundException("Market not found"));
  }

  @CacheEvict(value = "market", key = "#id")
  public void evict(Long id) {}
}

Async Processing

Requires @EnableAsync on a configuration class.

@Service
public class NotificationService {
  @Async
  public CompletableFuture<Void> sendAsync(Notification notification) {
    // send email/SMS
    return CompletableFuture.completedFuture(null);
  }
}

Logging (SLF4J)

@Service
public class ReportService {
  private static final Logger log = LoggerFactory.getLogger(ReportService.class);

  public Report generate(Long marketId) {
    log.info("generate_report marketId={}", marketId);
    try {
      // logic
    } catch (Exception ex) {
      log.error("generate_report_failed marketId={}", marketId, ex);
      throw ex;
    }
    return new Report();
  }
}

Middleware / Filters

@Component
public class RequestLoggingFilter extends OncePerRequestFilter {
  private static final Logger log = LoggerFactory.getLogger(RequestLoggingFilter.class);

  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
      FilterChain filterChain) throws ServletException, IOException {
    long start = System.currentTimeMillis();
    try {
      filterChain.doFilter(request, response);
    } finally {
      long duration = System.currentTimeMillis() - start;
      log.info("req method={} uri={} status={} durationMs={}",
          request.getMethod(), request.getRequestURI(), response.getStatus(), duration);
    }
  }
}

Pagination and Sorting

PageRequest page = PageRequest.of(pageNumber, pageSize, Sort.by("createdAt").descending());
Page<Market> results = marketService.list(page);

Error-Resilient External Calls

public <T> T withRetry(Supplier<T> supplier, int maxRetries) {
  int attempts = 0;
  while (true) {
    try {
      return supplier.get();
    } catch (Exception ex) {
      attempts++;
      if (attempts >= maxRetries) {
        throw ex;
      }
      try {
        Thread.sleep((long) Math.pow(2, attempts) * 100L);
      } catch (InterruptedException ie) {
        Thread.currentThread().interrupt();
        throw ex;
      }
    }
  }
}

Rate Limiting (Filter + Bucket4j)

Security Note: The X-Forwarded-For header is untrusted by default because clients can spoof it.
Only use forwarded headers when:

Your app is behind a trusted reverse proxy (nginx, AWS ALB, etc.)

You have registered ForwardedHeaderFilter as a bean

You have configured server.forward-headers-strategy=NATIVE or FRAMEWORK in application properties

Your proxy is configured to overwrite (not append to) the X-Forwarded-For header

When ForwardedHeaderFilter is properly configured, request.getRemoteAddr() will automatically
return the correct client IP from the forwarded headers. Without this configuration, use
request.getRemoteAddr() directly—it returns the immediate connection IP, which is the only
trustworthy value.

@Component
public class RateLimitFilter extends OncePerRequestFilter {
  private final Map<String, Bucket> buckets = new ConcurrentHashMap<>();

  /*
   * SECURITY: This filter uses request.getRemoteAddr() to identify clients for rate limiting.
   *
   * If your application is behind a reverse proxy (nginx, AWS ALB, etc.), you MUST configure
   * Spring to handle forwarded headers properly for accurate client IP detection:
   *
   * 1. Set server.forward-headers-strategy=NATIVE (for cloud platforms) or FRAMEWORK in
   *    application.properties/yaml
   * 2. If using FRAMEWORK strategy, register ForwardedHeaderFilter:
   *
   *    @Bean
   *    ForwardedHeaderFilter forwardedHeaderFilter() {
   *        return new ForwardedHeaderFilter();
   *    }
   *
   * 3. Ensure your proxy overwrites (not appends) the X-Forwarded-For header to prevent spoofing
   * 4. Configure server.tomcat.remoteip.trusted-proxies or equivalent for your container
   *
   * Without this configuration, request.getRemoteAddr() returns the proxy IP, not the client IP.
   * Do NOT read X-Forwarded-For directly—it is trivially spoofable without trusted proxy handling.
   */
  @Override
  protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response,
      FilterChain filterChain) throws ServletException, IOException {
    // Use getRemoteAddr() which returns the correct client IP when ForwardedHeaderFilter
    // is configured, or the direct connection IP otherwise. Never trust X-Forwarded-For
    // headers directly without proper proxy configuration.
    String clientIp = request.getRemoteAddr();

    Bucket bucket = buckets.computeIfAbsent(clientIp,
        k -> Bucket.builder()
            .addLimit(Bandwidth.classic(100, Refill.greedy(100, Duration.ofMinutes(1))))
            .build());

    if (bucket.tryConsume(1)) {
      filterChain.doFilter(request, response);
    } else {
      response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
    }
  }
}

Background Jobs

Use Spring’s @Scheduled or integrate with queues (e.g., Kafka, SQS, RabbitMQ). Keep handlers idempotent and observable.

Observability

Structured logging (JSON) via Logback encoder

Metrics: Micrometer + Prometheus/OTel

Tracing: Micrometer Tracing with OpenTelemetry or Brave backend

Production Defaults

Prefer constructor injection, avoid field injection

Enable spring.mvc.problemdetails.enabled=true for RFC 7807 errors (Spring Boot 3+)

Configure HikariCP pool sizes for workload, set timeouts

Use @Transactional(readOnly = true) for queries

Enforce null-safety via @NonNull and Optional where appropriate

Remember: Keep controllers thin, services focused, repositories simple, and errors handled centrally. Optimize for maintainability and testability.
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