Null Safety JSpecify annotations for compile-time null safety Package-level @NullMarked annotation HTTP Interface Clients Declarative HTTP clients with @HttpExchange Replace RestTemplate/WebClient boilerplate Bean Registration Programmatic bean registration BeanRegistrar interface API Versioning First-class API versioning support Media type parameter versioning JMS Client JMS messaging with Apache Artemis Producer/Consumer patterns Resilience Built-in resilience without external dependencies @Retryable and @ConcurrencyLimit Jackson 3 Jackson 3 JSON processing support ISO-8601 defaults, hint() method, JSON Views REST Test Client Unified REST API testing One API for unit, integration, and E2E tests MockMvcTester vs RestTestClient Comparing controller testing approaches Side-by-side examples and decision guide Spring Data AOT Ahead-of-time repository compilation 50-70% faster startup, compile-time validation OpenTelemetry Official observability starter Auto-instrumentation, log correlation, OTLP export Spring Security MFA Multi-factor authentication with Spring Security 7 @EnableMultiFactorAuthentication with OTT Auto-Configuration Modular auto-configuration changes Migration from Spring Boot 3.x