Advanced Spring
The infrastructure around the request path: security filters, the testing pyramid and Spring's test slices, Actuator and Micrometer, AOP, application events and messaging, and scheduled and async execution.
Spring Security: The Filter Chain in Ten Minutes
Where security sits relative to your controllers, why a @ControllerAdvice never sees a 401, and the minimum configuration for a stateless API.
Testing Spring Boot: Slices, Mocks and Real Infrastructure
Which test annotation to reach for, why @SpringBootTest everywhere makes a slow suite, and how Testcontainers replaced H2 for repository tests.
Actuator and Micrometer: Making a Service Observable
The endpoints worth exposing, why liveness and readiness are different questions, custom metrics with Micrometer, and keeping label cardinality under control.
Spring AOP: The Mechanism Behind @Transactional
Pointcuts, advice types, and why proxy-based AOP cannot intercept a self-call — the limitation that explains three earlier guides at once.
Events and Messaging: In-Process, Then Across Services
Spring's application events, the @TransactionalEventListener that fixes the commit-then-publish problem, and what changes when a real broker is involved.
Scheduling and @Async: The Default Executor Is a Hazard
Fixed-rate versus fixed-delay, cron that means what you think, why @Async needs a configured pool, and what happens when four instances share a job.