Spring Boot Quiz: @Cacheable with Proxy Calls

When calling findByIdWithFallback(), is the result cached?

• A) Yes, always cached

• B) No, caching is bypassed

• C) Only on first call

• D) Depends on cache configuration

Answer

Answer is B) No, caching is bypassed

In Spring @Cacheable annotation, like other Spring AOP (Aspect-oriented programming) annotations such as `@Transactional`, is implemented using proxying.

• When the spring application context starts, it creates a proxy object around the original UserService bean.

• When a method is annotated with @Cacheable (like findById) is called externally on the UserService bean, the call goes through this proxy.

• The proxy intercepts the call, executes the caching logic (checking the cache, and if missed, calling the original method and storing the result), and then forwards the call to the original bean’s method if necessary.

In the scenario provided above:

• A call is made to findByIdWithFallback(id). This call is made on the proxy of UserService.

• The findByIdWithFallback method itself does not have the @Cacheable annotation, so the proxy simply calls the original method implementation on the target UserService bean.

• Inside the UserService bean, the findByIdWithFallback method performs an internal call to findById(id) using the this reference: return findById(id);.

• This internal call bypasses the proxy. Since the call is not routed through the proxy, the Spring AOP interceptor responsible for the @Cacheable logic is never executed.

• Therefore, the findById method’s caching is bypassed when called internally from another method within the same object (findByIdWithFallback).

How can we fix this?

Injecting the Proxy (Self-Injection):

To ensure the caching logic is applied to the findById method even from the findByIdWithFallback method, we must route the internal call through the proxy.

Add @Cacheable on findByIdWithFallback method:

• External Call to findByIdWithFallback(id)is intercepted by the proxy. Proxy checks the cache for findByIdWithFallback(id).

Cache Hit: The cached result for findByIdWithFallback is returned.
The original method is skipped.

Cache Miss: The original findByIdWithFallback The method is executed.
This method then internally calls this.findById(id).