WebClient vs RestTemplate — Reactive vs Blocking HTTP Clients
Fast recall
Quick revision
Core answer
WebClient for new code. `WebClient` is the reactive, non-blocking client built on Reactor and Netty — returns Mono / Flux, supports streaming bodies, integrates explicit backpressure and Retry.backoff operators, and works correctly on both WebFlux and MVC stacks. In 2026 the choice is simple: use WebClient for any new code (it can be used in blocking style with .block() if needed); only keep RestTemplate in legacy MVC services where the cost of migration outweighs the benefit. `RestClient` (Spring 6.1+) is the modern blocking alternative if you want fluent API without reactive types.Whether you know the official deprecation status, the WebFlux/MVC compatibility story, and when RestClient is the right answer instead of WebClient
Using RestTemplate in WebFlux (it blocks the event loop), or assuming WebClient is only for reactive applications
Mention RestClient as the modern fluent blocking client, discuss connection pool tuning per upstream, and explain why one WebClient instance per upstream is the right pattern
Interview-ready guide
Interview answer
Spring has three HTTP clients today, and the choice is simple in 2026.
`RestTemplate`:
- Original blocking client; in maintenance mode since Spring 5
- No new features; only critical bug fixes
- Avoid for new code
- Never use it in WebFlux — it blocks the event loop
`WebClient`:
- Reactive, non-blocking, built on Reactor Netty
- Returns
Mono/Flux; supports streaming bodies and backpressure - Recommended for any new code
- Works on both WebFlux (native) and MVC (with
.block())
`RestClient` (Spring 6.1+):
- Modern fluent blocking API — same builder shape as
WebClientbut returns plain values - Right choice for MVC services or virtual-thread services that want clean blocking ergonomics
Decision rule:
- WebFlux →
WebClient - MVC, fluent API desired →
RestClient - MVC, planning to migrate →
WebClientwith.block() - Legacy MVC with many
RestTemplatecalls → don't migrate aggressively; cost-benefit
Production essentials regardless of client:
- One client bean per upstream; separate connection pools
- Explicit timeouts on every call
- Retry with backoff and filtering for idempotent operations
- Circuit breaker (Resilience4j) around external calls
- Micrometer / OpenTelemetry instrumentation
The strategic answer: pick WebClient for new code unless you specifically want blocking ergonomics, in which case RestClient is the modern choice. Never use RestTemplate in WebFlux.
- Configure one client per upstream with proper timeouts and retries — the client choice matters less than the production hygiene around it.
WebClient vs RestTemplate — Reactive vs Blocking HTTP Clients
Direct Answer
RestTemplate is Spring's classic blocking HTTP client — synchronous, thread-per-call, simple to use. It is officially in maintenance mode since Spring 5; Spring recommends WebClient for new code. WebClient is the reactive, non-blocking client built on Reactor and Netty — returns Mono / Flux, supports streaming bodies, integrates explicit backpressure and Retry.backoff operators, and works correctly on both WebFlux and MVC stacks. In 2026 the choice is simple: use WebClient for any new code (it can be used in blocking style with .block() if needed); only keep RestTemplate in legacy MVC services where the cost of migration outweighs the benefit. RestClient (Spring 6.1+) is the modern blocking alternative if you want fluent API without reactive types.
Common Mistakes & Pitfalls
Using RestTemplate in WebFlux (it blocks the event loop), or assuming WebClient is only for reactive applications
Check your understanding
Answer these without looking back at the article.
- What is RestClient and how does it differ from WebClient?
- Why is using RestTemplate in a WebFlux service a bug?
- How do you configure connection pool size for WebClient per upstream?
- How does Resilience4j integrate with WebClient for circuit breaking?
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