Spring Guidelines — S3Mock

Canonical reference for Spring Boot idioms, patterns, and code quality standards used across this project.

Bean Registration

Register beans explicitly in @Configuration classes using @Bean factory methods — not via component scanning or class-level @Service/@Component annotations.

@Configuration
class ServiceConfiguration {
  @Bean
  fun bucketService(bucketStore: BucketStore, objectStore: ObjectStore): BucketService =
    BucketService(bucketStore, objectStore)
}

Three configuration layers mirror the architecture:

• StoreConfiguration — store beans
• ServiceConfiguration — service beans (imported in @SpringBootTest)
• ControllerConfiguration — controller, filter, and exception-handler beans

Dependency Injection

Always use constructor injection. Never use @Autowired on fields or setters in production code.

// DO — constructor injection
class BucketService(
  private val bucketStore: BucketStore,
  private val objectStore: ObjectStore,
)

// DON'T — field injection
class BucketService {
  @Autowired private lateinit var bucketStore: BucketStore
}

Controllers

• @RestController classes map HTTP only — never contain business logic
• All logic is delegated to a @Service; controllers call the service and return the result
• Return typed DTOs, never raw strings
• Controllers never catch exceptions — exception handlers in ControllerConfiguration do that

// DO
@GetMapping("/{bucketName}")
fun getBucket(@PathVariable bucketName: String): ResponseEntity<ListBucketResult> =
  ResponseEntity.ok(bucketService.listObjects(bucketName))

// DON'T
@GetMapping("/{bucketName}")
fun getBucket(@PathVariable bucketName: String): String {
  // business logic here ...
  return "<ListBucketResult>...</ListBucketResult>"
}

Configuration Properties

Bind configuration via @ConfigurationProperties data classes — never inject individual values with @Value in production code.

@JvmRecord
@ConfigurationProperties("com.adobe.testing.s3mock.store")
data class StoreProperties(
  @param:DefaultValue("false") val retainFilesOnExit: Boolean,
  @param:DefaultValue("us-east-1") val region: Region,
)

Enable each properties class with @EnableConfigurationProperties in the matching @Configuration:

@Configuration
@EnableConfigurationProperties(StoreProperties::class)
class StoreConfiguration { ... }

Profiles

S3Mock uses Spring Boot profile groups to compose behaviour:

Profile	Activates	Purpose
debug	actuator	Debug-level logging + full actuator
trace	actuator	Trace-level logging + full actuator
actuator	—	JMX + all actuator endpoints exposed

Profile groups are defined in application.properties:

spring.profiles.group.debug=actuator
spring.profiles.group.trace=actuator

Profile-specific properties files:

• application-debug.properties — logging levels only
• application-trace.properties — logging levels only
• application-actuator.properties — JMX and actuator endpoint settings

Actuator endpoints are disabled by default (management.endpoints.access.default=none in application.properties). The actuator profile overrides this to unrestricted.

Exception Handling

• Services throw S3Exception constants (e.g., S3Exception.NO_SUCH_BUCKET) — never create new exception classes
• Exception handlers are @ControllerAdvice classes registered as @Beans in ControllerConfiguration
• S3MockExceptionHandler converts S3Exception → XML ErrorResponse with the correct HTTP status
• IllegalStateExceptionHandler converts unexpected errors → 500 InternalError

@ControllerAdvice
class S3MockExceptionHandler : ResponseEntityExceptionHandler() {
  @ExceptionHandler(S3Exception::class)
  fun handleS3Exception(s3Exception: S3Exception): ResponseEntity<ErrorResponse> { ... }
}

Testing

Service and Store Tests — @SpringBootTest

Use @SpringBootTest scoped to the relevant @Configuration class with @MockitoBean for dependencies.

@SpringBootTest(classes = [ServiceConfiguration::class], webEnvironment = SpringBootTest.WebEnvironment.NONE)
@MockitoBean(types = [MultipartService::class, MultipartStore::class])
internal class BucketServiceTest : ServiceTestBase() {
  @Autowired private lateinit var iut: BucketService

  @Test
  fun `should return no such bucket`() { ... }
}

Always extend the appropriate base class:

• ServiceTestBase — service layer tests
• StoreTestBase — store layer tests

Controller Tests — @WebMvcTest

Use @WebMvcTest scoped to the controller under test with @MockitoBean for services and BaseControllerTest for shared fixtures.

@WebMvcTest(controllers = [BucketController::class], ...
@MockitoBean(types = [BucketService::class])
internal class BucketControllerTest : BaseControllerTest() {
  @Autowired private lateinit var mockMvc: MockMvc
  @Autowired private lateinit var bucketService: BucketService

  @Test
  fun `should list buckets`() { ... }
}

Common Anti-Patterns

Anti-Pattern	Refactor To
@ExtendWith(MockitoExtension::class) + @Mock + @InjectMocks	@SpringBootTest + @MockitoBean + @Autowired
@Autowired field injection in production code	Constructor injection
Business logic in controller method	Delegate to a service class
Returning a raw String from a controller	Return a typed DTO wrapped in ResponseEntity
@Value("${property}") scattered throughout beans	@ConfigurationProperties data class
New exception class for S3 errors	S3Exception constant