Java coding standards for Spring Boot services: naming, immutability, Optional usage, streams, exceptions, generics, and project layout.
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Standards for readable, maintainable Java (17+) code in Spring Boot and Quarkus services.
Before applying standards, determine the framework from the build file:
quarkus → apply [QUARKUS] conventionsspring-boot → apply [SPRING] conventionsThe sections below show concrete Spring Boot, Quarkus, and shared Java examples for naming, immutability, dependency injection, reactive code, exceptions, project layout, logging, configuration, and tests.
// PASS: Classes/Records: PascalCase
public class MarketService {}
public record Money(BigDecimal amount, Currency currency) {}
// PASS: Methods/fields: camelCase
private final MarketRepository marketRepository;
public Market findBySlug(String slug) {}
// PASS: Constants: UPPER_SNAKE_CASE
private static final int MAX_PAGE_SIZE = 100;
// PASS: [QUARKUS] JAX-RS resources named as *Resource, not *Controller
public class MarketResource {}
// PASS: [SPRING] REST controllers named as *Controller
public class MarketController {}
// PASS: Favor records and final fields
public record MarketDto(Long id, String name, MarketStatus status) {}
public class Market {
private final Long id;
private final String name;
// getters only, no setters
}
// PASS: [QUARKUS] Panache active-record entities use public fields (Quarkus convention)
@Entity
public class Market extends PanacheEntity {
public String name;
public MarketStatus status;
// Panache generates accessors at build time; public fields are idiomatic here
}
// PASS: [QUARKUS] Panache MongoDB entities
@MongoEntity(collection = "markets")
public class Market extends PanacheMongoEntity {
public String name;
public MarketStatus status;
}
// PASS: Return Optional from find* methods
// [SPRING]
Optional<Market> market = marketRepository.findBySlug(slug);
// [QUARKUS] Panache
Optional<Market> market = Market.find("slug", slug).firstResultOptional();
// PASS: Map/flatMap instead of get()
return market
.map(MarketResponse::from)
.orElseThrow(() -> new EntityNotFoundException("Market not found"));
// PASS: Use streams for transformations, keep pipelines short
List<String> names = markets.stream()
.map(Market::name)
.filter(Objects::nonNull)
.toList();
// FAIL: Avoid complex nested streams; prefer loops for clarity
// PASS: [SPRING] Constructor injection (preferred over @Autowired on fields)
@Service
public class MarketService {
private final MarketRepository marketRepository;
public MarketService(MarketRepository marketRepository) {
this.marketRepository = marketRepository;
}
}
// PASS: [QUARKUS] Constructor injection
@ApplicationScoped
public class MarketService {
private final MarketRepository marketRepository;
@Inject
public MarketService(MarketRepository marketRepository) {
this.marketRepository = marketRepository;
}
}
// PASS: [QUARKUS] Package-private field injection (acceptable in Quarkus — avoids proxy issues)
@ApplicationScoped
public class MarketService {
@Inject
MarketRepository marketRepository;
}
// FAIL: [SPRING] Field injection with @Autowired
@Autowired
private MarketRepository marketRepository; // use constructor injection
// FAIL: [QUARKUS] @Singleton when interception or lazy init is needed
@Singleton // non-proxyable — use @ApplicationScoped instead
public class MarketService {}
// PASS: Return Uni/Multi from reactive endpoints
@GET
@Path("/{slug}")
public Uni<Market> findBySlug(@PathParam("slug") String slug) {
return Market.find("slug", slug)
.<Market>firstResult()
.onItem().ifNull().failWith(() -> new MarketNotFoundException(slug));
}
// PASS: Non-blocking pipeline composition
public Uni<OrderConfirmation> placeOrder(OrderRequest req) {
return validateOrder(req)
.chain(valid -> persistOrder(valid))
.chain(order -> notifyFulfillment(order));
}
// FAIL: Blocking call inside a Uni/Multi pipeline
public Uni<Market> find(String slug) {
Market m = Market.find("slug", slug).firstResult(); // BLOCKING — breaks event loop
return Uni.createFrom().item(m);
}
// FAIL: Subscribing more than once to a shared Uni
Uni<Market> shared = fetchMarket(slug);
shared.subscribe().with(m -> log(m));
shared.subscribe().with(m -> cache(m)); // double subscribe — use Uni.memoize()
MarketNotFoundException)catch (Exception ex) unless rethrowing/logging centrallythrow new MarketNotFoundException(slug);
// [SPRING]
@RestControllerAdvice
public class GlobalExceptionHandler {
@ExceptionHandler(MarketNotFoundException.class)
public ResponseEntity<ErrorResponse> handle(MarketNotFoundException ex) {
return ResponseEntity.status(404).body(ErrorResponse.from(ex));
}
}
// [QUARKUS] Option A: ExceptionMapper
@Provider
public class MarketNotFoundMapper implements ExceptionMapper<MarketNotFoundException> {
@Override
public Response toResponse(MarketNotFoundException ex) {
return Response.status(404).entity(ErrorResponse.from(ex)).build();
}
}
// [QUARKUS] Option B: @ServerExceptionMapper (RESTEasy Reactive)
@ServerExceptionMapper
public RestResponse<ErrorResponse> handle(MarketNotFoundException ex) {
return RestResponse.status(Status.NOT_FOUND, ErrorResponse.from(ex));
}
public <T extends Identifiable> Map<Long, T> indexById(Collection<T> items) { ... }
src/main/java/com/example/app/
config/
controller/
service/
repository/
domain/
dto/
util/
src/main/resources/
application.yml
src/test/java/... (mirrors main)
src/main/java/com/example/app/
config/ # @ConfigMapping, @ConfigProperty beans, Producers
resource/ # JAX-RS resources (not "controller")
service/
repository/ # PanacheRepository implementations (if not using active record)
domain/ # JPA/Panache entities, MongoDB entities
dto/
util/
mapper/ # MapStruct mappers (if used)
src/main/resources/
application.properties # Quarkus convention (YAML supported with quarkus-config-yaml)
import.sql # Hibernate auto-import for dev/test
src/test/java/... (mirrors main)
@Singleton where @ApplicationScoped is intended — breaks proxying and interceptionquarkus-resteasy-reactive and quarkus-resteasy (classic) — pick one stack// [SPRING] SLF4J
private static final Logger log = LoggerFactory.getLogger(MarketService.class);
log.info("fetch_market slug={}", slug);
log.error("failed_fetch_market slug={}", slug, ex);
// [QUARKUS] JBoss Logging (default, zero-cost at build time)
private static final Logger log = Logger.getLogger(MarketService.class);
log.infof("fetch_market slug=%s", slug);
log.errorf(ex, "failed_fetch_market slug=%s", slug);
// [QUARKUS] Alternative: simplified logging with @Inject
@Inject
Logger log; // CDI-injected, scoped to declaring class
@Nullable only when unavoidable; otherwise use @NonNull@NotNull, @NotBlank) on inputs@Valid on @BeanParam, @RestForm, and request body parameters// [SPRING] @ConfigurationProperties
@ConfigurationProperties(prefix = "market")
public record MarketProperties(int maxPageSize, Duration cacheTtl) {}
// [QUARKUS] @ConfigMapping (type-safe, build-time validated)
@ConfigMapping(prefix = "market")
public interface MarketConfig {
int maxPageSize();
Duration cacheTtl();
}
// [QUARKUS] Simple values with @ConfigProperty
@ConfigProperty(name = "market.max-page-size", defaultValue = "100")
int maxPageSize;
@WebMvcTest for controller slices, @DataJpaTest for repository slices@SpringBootTest reserved for full integration tests@MockBean for replacing beans in Spring context@QuarkusTest)@QuarkusTest reserved for CDI integration tests@InjectMock for replacing CDI beans in integration tests@QuarkusTestResource for custom external service lifecycle// [SPRING] Controller test
@WebMvcTest(MarketController.class)
class MarketControllerTest {
@Autowired MockMvc mockMvc;
@MockBean MarketService marketService;
}
// [QUARKUS] Integration test
@QuarkusTest
class MarketResourceTest {
@InjectMock
MarketService marketService;
@Test
void should_return_404_when_market_not_found() {
given().when().get("/markets/unknown").then().statusCode(404);
}
}
// [QUARKUS] Unit test (no CDI, no @QuarkusTest)
@ExtendWith(MockitoExtension.class)
class MarketServiceTest {
@Mock MarketRepository marketRepository;
@InjectMocks MarketService marketService;
}
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