UpdatedAug 5, 2026

Spring Boot Caching

Question Variations

"Why does `@Cacheable` sometimes appear not to run?"
"How should cache invalidation relate to writes?"
"When is a local cache unsafe in a distributed service?"

Why This Is Asked

Caching annotations are concise, but their correctness depends on keys, invalidation, proxying, and distributed deployment behavior.

Key Concepts

@Cacheable reuses a value based on a cache key.
@CacheEvict and @CachePut support deliberate mutation policies.
Self-invocation bypasses proxy-based cache annotations.
A multi-instance application needs a shared cache when consistency requires it.

Question Variations

“Why does @Cacheable sometimes appear not to run?”
“How should cache invalidation relate to writes?”
“When is a local cache unsafe in a distributed service?”

Answers by Technology

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Expected Answer (Spring Boot 4.1.0 / Java 17+)

Enable Spring’s caching abstraction, then use @Cacheable on a read whose result is safe to reuse with a deliberate key. Pair writes with @CacheEvict or another invalidation policy so stale values do not persist indefinitely. The annotations are proxy-based, so a call from one method to another on the same object bypasses interception. In a multi-instance deployment, choose a shared cache if instances must observe a consistent invalidation policy.

Why It Matters

Caching reduces load only when keys, expiry, and invalidation match the data’s correctness requirements.

Code Example

@Service
class ProductService {
  @Cacheable(cacheNames = "products", key = "#id")
  Product findById(UUID id) { return load(id); }
  private Product load(UUID id) { return new Product(id); }
}

Common Mistakes

Expecting self-invocation to cache: The proxy is bypassed.
Caching mutable data with no invalidation plan: Clients receive stale or incorrect results.

Follow-up Questions

Why use a shared cache in a fleet? (Answer: To coordinate cached state across instances.)
What does @CacheEvict do? (Answer: Removes entries when mutation makes them stale.)