When do you choose Spring MVC versus Spring WebFlux?

Chooses between blocking Servlet execution and end-to-end non-blocking reactive execution based on dependencies, concurrency, and team cost.

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TL;DR

Spring MVC uses the Servlet model and assumes request handling may block, so a container thread pool absorbs concurrent blocking work. WebFlux is designed for non-blocking I/O and uses a small event-loop-style worker set with reactive composition. I choose MVC for ordinary imperative applications with blocking dependencies such as JDBC or JPA. I consider WebFlux when the path is genuinely non-blocking end to end and must hold many concurrent slow I/O operations efficiently.

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Concurrency models, blocking boundaries, reactive composition, capacity, and evidence-based framework selection.

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Core answer
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Overview
The meaningful choice is the execution model across the whole request path, not which controller annotation looks newer.
Spring MVC uses the Servlet model and assumes request handling may block, so a container thread pool absorbs concurrent blocking work. WebFlux is designed for non-blocking I/O and uses a small event-loop-style worker set with reactive composition. I choose MVC for ordinary imperative applications with blocking dependencies such as JDBC or JPA. I consider WebFlux when the path is genuinely non-blocking end to end and must hold many concurrent slow I/O operations efficiently.
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Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
Putting a blocking repository call on a WebFlux event-loop thread can stall many requests, so returning Mono does not make blocking work non-blocking. MVC can still use WebClient and supported async return types for selected remote-call patterns. WebFlux adds Reactor semantics, context propagation concerns, and a steeper debugging model. Neither stack makes CPU-bound work faster, and non-blocking code can add overhead when concurrency does not justify it.

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Details

Claiming WebFlux is always faster.
Calling blocking APIs on event-loop threads.
Choosing WebFlux because a controller can return Mono.

When do you choose Spring MVC versus Spring WebFlux?

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