Why Spring Framework 7.0.4’s Hidden Bugs and Speed Boosts Matter to You

Deadlock Root Cause #36260

In a Kubernetes pod, a Spring 7.0.0‑7.0.3 application sometimes hangs after the pod is recreated: the process stays alive, the port never opens, and the log ends with Initializing Spring DispatcherServlet. A thread dump shows two threads— AbstractApplicationContext.close() and the JVM ShutdownHook —waiting on each other, forming a classic deadlock. The bug occurs when a SIGTERM triggers graceful shutdown, close() starts, and before it finishes the kubelet sends SIGKILL, which also activates the JVM shutdown hook. Both paths compete for the same lock, causing a probabilistic deadlock that only appears under container‑orchestrated environments.

The Spring team fixed it in 7.0.4 by rewriting the ConfigurableApplicationContext state machine, introducing an independent shutdown flag and CAS‑based guard so that whichever path arrives second simply yields, eliminating the lock contention.

Other Notable Bugs Fixed

#36293 – ConcurrentReferenceHashMap lock contention in high‑concurrency scenarios caused invisible throughput drops.

#36298 – Header modifications in HandlerInterceptor were not propagated to downstream services because HttpEntity parsing ignored the mutated headers.

#36266 – StompBrokerRelayMessageHandler failed to reconnect after the broker restarted, requiring a full application restart.

#36285 / #36226 – Message converters now accept MIME wildcards (*/*) and HeadersAdapter.remove() returns null instead of an empty list, preventing subtle bugs in edge cases.

Performance Optimizations in 7.0.4

Spring 7.0.4 delivers three dimensions of speed improvements that combine multiplicatively, yielding 30‑50 % faster startup and 10‑20 % lower request latency for typical workloads.

Routing hash algorithm rewrite – a more efficient hash reduces URL‑mapping lookup cost by about 5 % at million‑QPS scale.

Bean‑lookup path shortening – HandlerMethod parsing drops redundant intermediate objects, shaving off reflection overhead.

Fast‑path for simple @RequestMapping patterns – most single‑URL mappings bypass generic pattern matching.

Version‑mapping decoupling – API‑version checks no longer add extra overhead.

Annotation‑parsing cache – the first parse of method annotations is cached; subsequent calls reuse the cached data instead of re‑reflecting.

Validation reflection reduction – Bean Validation group checks now avoid repeated Class.getAnnotations() calls, benefitting bulk‑import scenarios.

Community benchmarks using spring-petclinic confirm the claimed gains.

How to Detect the Deadlock Issue

Pod starts but remains stuck; the process does not exit. jstack shows close() and ShutdownHook threads waiting on each other.

The problem only reproduces in K8s/container environments, not locally.

Higher deployment frequency increases occurrence probability.

Upgrade Decision Guidance

For projects running Spring 7.x on Kubernetes, upgrade to 7.0.4 immediately—deadlock fixes and performance gains are essential with near‑zero risk. For traditional deployments, the upgrade can be scheduled for the next iteration. Projects still on Spring 6.x / Boot 3.x should postpone the jump until they have completed JDK ≥ 17, migrated all dependencies to Jakarta namespaces, and reviewed the official migration guide.

JDK Version Impact

JDK 17 – ~10‑15 % startup boost (only routing and annotation cache improvements).

JDK 21 – ~25‑35 % boost (virtual‑thread support available but not fully optimized).

JDK 25 – ~40‑50 % boost (full virtual‑thread and Reactor 2025.0.3 optimizations).

Additional dependency upgrades (Micrometer 1.6.3, ASM 9.9.1, Apache POI 5.5) may affect specific use cases such as monitoring or large Excel exports.