Your async operations freeze under high load because the ThreadPoolTaskExecutor is undersized, causing deadlocks when tasks depend on each other. Fix the thread pool configuration.
Your service is hitting 'too many connections' in production. Root cause: connections are not closed correctly, causing leaks.
Your in-memory cache keeps growing and retains old objects forever, eventually triggering OutOfMemoryError. Fix by adding eviction.
Circular dependencies between @Service classes cause Spring to fail at startup. You must remove the circular reference via interface extraction or constructor redesign.
Your microservice uses RestTemplate (blocking), creating thread starvation under load. Convert to WebClient (reactive) for non-blocking IO.
Method returns null without null-safety checks, causing NPE in production.
FileInputStream is not closed, causing resource leaks and file handle exhaustion.
Modifying collection while iterating causes ConcurrentModificationException.
Static collection retains object references forever, preventing garbage collection.
Two threads acquire locks in different order, causing deadlock.
Transaction doesn't rollback on checked exception, causing data inconsistency.
Accessing lazy-loaded relationships outside transaction causes LazyInitializationException.
Two beans depend on each other, causing circular dependency error.
String concatenation in loop creates many intermediate objects, causing memory issues.
Double-checked locking pattern fails due to visibility issues without volatile.
POST request fails due to missing CSRF token in Spring Security.
Large objects are retained in memory longer than needed, causing OutOfMemoryError.
ThreadLocal values are not cleared, causing memory leaks in thread pools.
Actuator endpoints are exposed without authentication, leaking sensitive information.
Fetching entities with relationships triggers N+1 queries, causing performance issues.
Cache is not evicted when data is updated, serving stale data.
Bidirectional relationship causes infinite recursion during JSON serialization.
Application context is not properly closed, preventing cleanup and resource release.
Accessing entity after session is closed causes LazyInitializationException.
Multiple auto-configurations conflict, causing bean creation errors.
Too many classes loaded or class metadata retained, causing PermGen/Metaspace exhaustion.