Spring Framework 7 ships @Retryable and @ConcurrencyLimit in the core. Every behaviour counted invocation by invocation: a maxRetries that means one more call than you think, a timeout that does not time anything out, jitter that only adds, a CompletableFuture that is never retried, and what is still Resilience4j's job.
Where a Spring Boot 4 error body actually comes from, what spring.mvc.problemdetails.enabled does and does not cover, and a thirteen-failure matrix under five setups, plus the ways a tidy ProblemDetail setup hides 500s, leaks internals, or changed underneath you in Spring Framework 7.
Probes, graceful shutdown, resource limits and JVM ergonomics for Spring Boot 4, measured on a real cluster: a dependency outage under three probe setups, a rolling restart under load four ways, what the JVM decides for nine pod shapes, why CPU limits throttle your garbage collector, and an HPA scaling on a custom Micrometer metric.
One Spring Boot 4 service packaged nine ways (fat jar, layered on Temurin, Alpine and distroless, jlink, the JDK 25 AOT cache, buildpacks and Jib) and measured the same way: size on disk and over the wire, what a one-line change costs to push, startup, who the process runs as, and the failure each variant is most likely to hand you.
All seven propagation values with runnable proof and transaction-manager logs, the rollback rules, and why catching an inner failure still ends in UnexpectedRollbackException. Plus six ways @Transactional is present, correct, and inert — two of which commit work the code was trying to abandon — and why Propagation.NESTED cannot be used with JpaTransactionManager at all. Spring Boot 4.1.1, JDK 25.
An aspect that does not fire produces no error and no log line. A full reference for the ten pointcut designators Spring AOP supports (generated from real matches) and the fourteen it rejects, the difference between JDK and CGLIB proxies measured side by side, and a gallery of six aspects that silently do nothing. Includes two corrections to the reference documentation. Spring Boot 4.1.1, AspectJ 1.9.25.1, JDK 25.
You set a value in application-prod.yaml, deployed with prod active, and the old value is still in effect. The reason is a single line of the documented precedence list: config data is item 3 and environment variables are item 5. A measured walk through the precedence stack, profile groups and multi-document files, config trees and Kubernetes ConfigMaps, and the spring.config.import ordering that overrides you rather than the other way round.
@Value and @ConfigurationProperties are different mechanisms, not two styles. A measured matrix of which property spellings actually resolve (including the widely repeated claim about @Value and relaxed binding, which is wrong inside Spring Boot), record constructor binding and defaults, validation, and the JDK 23 change that silently stops your IDE metadata being generated. Verified on Spring Boot 4.1.1 and JDK 25.
Spring Boot logs one startup number and hides four phases behind it. This walks through turning on the ApplicationStartup instrumentation that ships switched off, reading the step tree by self time rather than total duration — the mistake that makes people optimise a bean costing 10 ms instead of the one costing 504 — and then puts measured numbers on component scanning (0.11 ms per class inspected, whether or not it is a bean), on the silent truncation a 2048-step buffer performs on your recording, and on the JDK 25 AOT cache, which took 6.93 s to 4.82 s on the companion project without a line of application code changing.
Every Actuator endpoint on Spring Boot 4.1.1, what each one leaks, and how to secure it — measured rather than described. /actuator/env masks every value by default and heapdump is not exposed by include:"*" at all, but turn it on and it hands over 59 MB containing the credentials env just masked. Plus the three gates a request passes, a separate management port, custom indicators for a database, Kafka and an external API — and the naive Kafka health check that blocks for exactly 60.002 seconds because request.timeout.ms is not the property that bounds it.