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Spring / Spring gRPC Interview Questions

What is the difference between a blocking stub, a non-blocking async stub, and a future stub in generated gRPC client code?
Stub typeBehavior
Blocking stubSynchronous call; calling thread waits for the response
Async stubTakes a StreamObserver callback; non-blocking, supports all four call types
Future stubUnary calls return a ListenableFuture, useful for async/reactive composition

Choosing between them depends on the caller's threading model: a blocking stub is the simplest to reason about in a traditional Spring MVC controller thread, an async stub is needed for streaming calls or to avoid tying up a thread while waiting, and a future stub fits nicely when composing results with CompletableFuture-style pipelines or reactive chains.

Which stub type is required to make a server-streaming or bidirectional-streaming call?
What does a future stub's unary call return in Java?

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