When to Use Which ?

About

In modern Spring Boot applications, there are multiple options for making HTTP calls to other services: RestTemplate, WebClient, and OpenFeign. Each has its own strengths, limitations, and ideal use cases. Choosing the right one is important for achieving the desired performance, maintainability, and developer productivity.

Comparison

Aspect	RestTemplate	WebClient	OpenFeign
Nature	Synchronous, blocking client for REST calls	Reactive, non-blocking HTTP client supporting sync & async	Declarative, interface-based HTTP client
Best For	Simple, blocking service calls in synchronous applications	Reactive systems, high concurrency, streaming data, when non-blocking IO is required	Microservices communication where you want to call REST APIs using annotated interfaces
When to Use	- Legacy applications still using blocking I/O - Quick prototypes or small services where async is not needed - When you already have existing codebase with RestTemplate	- Applications built on Project Reactor (Spring WebFlux) - When you need async calls without blocking threads - High-performance, high-throughput API clients - Streaming data handling	- When you want minimal boilerplate for calling internal/external REST APIs - You have OpenAPI specs and can generate interfaces - Clear contract-driven development between services
When Not to Use	- New reactive systems - When handling thousands of concurrent requests efficiently is critical	- Fully synchronous codebases where reactive stack would add complexity without benefit	- Low-level control of requests/responses is required - For highly dynamic API calls where compile-time interface definitions are not feasible
Ease of Use	Medium — requires manual request creation, error handling, object mapping	Medium — fluent API but requires understanding of reactive concepts (Mono, Flux)	High — just define an interface with annotations and call methods
Performance Profile	Blocking — each request ties up a thread until response arrives	Non-blocking — event-loop model allows scaling with fewer threads	Blocking or non-blocking depending on underlying client (e.g., OkHttp, WebClient)
Integration with OpenAPI	Requires manual configuration or wrapper code	Possible with codegen but less common	Excellent — generated clients map directly to service interfaces
Typical Use Case Example	A Spring Boot monolith making synchronous HTTP calls to a single third-party API	A reactive microservice calling multiple APIs in parallel to aggregate results	An internal payment service calling account service via a generated API client
Future Outlook	Deprecated in favor of WebClient for new development	Preferred choice for modern Spring HTTP clients	Preferred for declarative, contract-based inter-service communication