Spring Boot 3.4: 모든 새로운 기능 상세 설명

# application.properties
# Enable structured logging in console
logging.structured.format.console=ecs

# Or for log files
logging.structured.format.file=logstash

@RestController
@RequestMapping("/api/demo")
public class LoggingController {

    // Logger injection via SLF4J
    private static final Logger logger = LoggerFactory.getLogger(LoggingController.class);

    @GetMapping("/action")
    public ResponseEntity<String> performAction(@RequestParam String userId) {
        // Log will be automatically formatted as structured JSON
        logger.info("Action performed by user: {}", userId);
        return ResponseEntity.ok("Action completed");
    }
}

# application.properties
# Graceful shutdown is now ON by default
# To restore previous behavior (immediate shutdown):
server.shutdown=immediate

# Configure maximum wait timeout (30s default)
spring.lifecycle.timeout-per-shutdown-phase=45s

@Configuration
public class LifecycleConfig {

    private static final Logger logger = LoggerFactory.getLogger(LifecycleConfig.class);

    @Bean
    public ApplicationListener<ContextClosedEvent> gracefulShutdownListener() {
        // This listener executes at shutdown start
        return event -> {
            logger.info("Graceful shutdown initiated - completing in-flight requests");
            // Custom logic: close connections, save state, etc.
        };
    }
}

# application.properties
# Enable virtual threads globally
spring.threads.virtual.enabled=true

@Service
public class AsyncService {

    private static final Logger logger = LoggerFactory.getLogger(AsyncService.class);

    // With virtual threads enabled, each blocking call
    // no longer consumes an OS thread
    public String fetchExternalData() {
        logger.info("Executing on thread: {}", Thread.currentThread());

        // Blocking HTTP call - with virtual threads,
        // the OS thread is released during I/O wait
        return restClient.get()
            .uri("https://api.external.com/data")
            .retrieve()
            .body(String.class);
    }
}

@Configuration
public class HttpClientConfig {

    @Bean
    public RestClient restClient(RestClient.Builder builder) {
        // Spring Boot automatically chooses implementation:
        // 1. Apache HTTP Components (if present)
        // 2. Jetty Client
        // 3. Reactor Netty
        // 4. JDK HttpClient (Java 11+)
        // 5. SimpleClientHttpRequestFactory (fallback)
        return builder
            .baseUrl("https://api.example.com")
            .defaultHeader("Accept", "application/json")
            .build();
    }
}

# application.properties
# Force specific implementation
spring.http.client.factory=jdk

# Configure redirect behavior
spring.http.client.redirects=dont-follow

@Configuration
public class CustomHttpClientConfig {

    @Bean
    public RestClient customRestClient(ClientHttpRequestFactoryBuilder factoryBuilder) {
        // Advanced factory configuration
        ClientHttpRequestFactory factory = factoryBuilder
            .httpComponents()
            .connectTimeout(Duration.ofSeconds(5))
            .readTimeout(Duration.ofSeconds(30))
            .build();

        return RestClient.builder()
            .requestFactory(factory)
            .baseUrl("https://api.example.com")
            .build();
    }
}

@WebMvcTest(UserController.class)
class UserControllerTest {

    @Autowired
    private MockMvcTester mockMvc; // New class!

    @Test
    void shouldReturnUserById() {
        // Fluent API with AssertJ
        mockMvc.get().uri("/api/users/{id}", 1)
            .assertThat()
            .hasStatusOk()
            .hasContentType(MediaType.APPLICATION_JSON)
            .bodyJson()
            .extractingPath("$.name")
            .isEqualTo("John Doe");
    }

    @Test
    void shouldReturn404ForUnknownUser() {
        mockMvc.get().uri("/api/users/{id}", 999)
            .assertThat()
            .hasStatus(HttpStatus.NOT_FOUND)
            .bodyJson()
            .extractingPath("$.error")
            .isEqualTo("User not found");
    }
}

@WebMvcTest(UserController.class)
class ComparisonTest {

    @Autowired
    private MockMvcTester mockMvcTester;

    @Autowired
    private MockMvc mockMvc;

    @Test
    void withMockMvcTester() {
        // New approach: fluent and concise
        mockMvcTester.post().uri("/api/users")
            .contentType(MediaType.APPLICATION_JSON)
            .content("{\"name\": \"Jane\"}")
            .assertThat()
            .hasStatus(HttpStatus.CREATED)
            .hasHeader("Location", "/api/users/2");
    }

    @Test
    void withClassicMockMvc() throws Exception {
        // Old approach: more verbose
        mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{\"name\": \"Jane\"}"))
            .andExpect(status().isCreated())
            .andExpect(header().string("Location", "/api/users/2"));
    }
}

# application.properties
# Use multiple Docker Compose files
spring.docker.compose.file=compose.yaml,compose-dev.yaml

# Pass arguments at startup
spring.docker.compose.start.arguments=--scale redis=2

# Arguments at shutdown
spring.docker.compose.stop.arguments=--timeout 60

# compose.yaml
services:
  postgres:
    image: postgres:16
    environment:
      POSTGRES_DB: myapp
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
    ports:
      - "5432:5432"

  redis-stack:
    image: redis/redis-stack:latest
    ports:
      - "6379:6379"
      - "8001:8001" # RedisInsight UI

  grafana-lgtm:
    image: grafana/otel-lgtm:latest
    ports:
      - "3000:3000"  # Grafana
      - "4317:4317"  # OTLP gRPC

@TestConfiguration(proxyBeanMethods = false)
public class IntegrationTestConfig {

    @Bean
    @ServiceConnection
    public PostgreSQLContainer<?> postgresContainer() {
        return new PostgreSQLContainer<>("postgres:16");
    }

    @Bean
    @ServiceConnection
    public RedisStackContainer redisStackContainer() {
        // New Redis Stack support
        return new RedisStackContainer("redis/redis-stack:latest");
    }

    @Bean
    @ServiceConnection
    public LgtmStackContainer observabilityContainer() {
        // New Grafana LGTM support (Loki, Grafana, Tempo, Mimir)
        return new LgtmStackContainer("grafana/otel-lgtm:latest");
    }
}

# application.properties
# Enable SSL information in actuator
management.info.ssl.enabled=true

# Configure warning threshold for expiring certificates
management.health.ssl.certificate-validity-warning-threshold=30d

@Configuration
public class SslMonitoringConfig {

    @Bean
    public HealthIndicator sslCertificateHealth(SslInfo sslInfo) {
        return () -> {
            // Custom certificate validity check
            boolean allValid = sslInfo.getBundles().values().stream()
                .flatMap(bundle -> bundle.getCertificates().stream())
                .allMatch(cert -> cert.getValidityEnds().isAfter(Instant.now()));

            return allValid
                ? Health.up().build()
                : Health.down().withDetail("reason", "Certificate expiring soon").build();
        };
    }
}

# application.properties
# Use gRPC for OTLP (traces and metrics)
management.otlp.tracing.transport=grpc
management.otlp.tracing.endpoint=http://localhost:4317

# New: group applications together
spring.application.group=payment-services

tasks.named("bootBuildImage") {
    // Native ARM support (new)
    imagePlatform = "linux/arm64"

    // New security flag
    trustBuilder = false

    // Image configuration
    imageName = "myregistry.com/myapp:${version}"
}

<!-- pom.xml -->
<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
        <image>
            <!-- Native ARM support -->
            <platform>linux/arm64</platform>
            <!-- Builder optimized for minimal images -->
            <builder>paketobuildpacks/builder-jammy-java-tiny</builder>
        </image>
    </configuration>
</plugin>

@ConfigurationProperties(prefix = "app")
@Validated
public class AppConfig {

    @NotBlank
    private String name;

    // IMPORTANT: @Valid required to cascade validation
    @Valid
    private DatabaseConfig database;

    // Without @Valid, ServerConfig constraints will NOT be checked
    private ServerConfig server;

    // Getters and setters
}

public class DatabaseConfig {
    @NotBlank
    private String url;

    @Min(1)
    private int poolSize;

    // Getters and setters
}

public class ServerConfig {
    @NotNull // This constraint will NOT be checked without @Valid on parent
    private Integer port;

    // Getters and setters
}

@SpringBootTest
class UserServiceTest {

    // New: native Mockito annotations
    @MockitoBean
    private UserRepository userRepository;

    @MockitoSpyBean
    private EmailService emailService;

    @Autowired
    private UserService userService;

    @Test
    void shouldCreateUser() {
        // Mock configuration
        when(userRepository.save(any())).thenReturn(new User(1L, "test@example.com"));

        userService.createUser("test@example.com");

        // Spy verification
        verify(emailService).sendWelcomeEmail("test@example.com");
    }
}