Choosing the Right Spring HTTP Client: RestTemplate vs WebClient vs RestClient

RestTemplate

RestTemplate is the original synchronous HTTP client provided by Spring. It wraps the low‑level java.net handling and offers convenience methods such as getForObject, postForEntity, exchange, etc., which automatically marshal request bodies and unmarshal responses using configured HttpMessageConverter s.

Key features

Synchronous API : Calls block the calling thread until a response is received.

Template‑method style : Pre‑defined methods for common HTTP verbs (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS).

Customizable : Interceptors, error handlers and message converters can be added via RestTemplateBuilder or directly on the instance.

Object mapping : JSON, XML, protobuf and other formats are converted to/from Java objects automatically.

Typical usage example

import org.springframework.web.client.RestTemplate;
import org.springframework.http.ResponseEntity;

public class RestTemplateExample {
    public static void main(String[] args) {
        RestTemplate restTemplate = new RestTemplate();
        String url = "https://funtester.com/1";
        ResponseEntity<String> response = restTemplate.getForEntity(url, String.class);
        if (response.getStatusCode().is2xxSuccessful()) {
            System.out.println("Response Body: " + response.getBody());
        } else {
            System.out.println("Request failed: " + response.getStatusCode());
        }
    }
}

Advantages

Easy to use : Minimal learning curve, ideal for quick prototypes and simple CRUD operations.

Full Spring integration : Works seamlessly with @RestController, MessageConverters, and other Spring components.

Limitations

Blocking nature : Not suitable for high‑concurrency scenarios because each request occupies a thread.

No reactive support : Cannot be used with Project Reactor or other non‑blocking pipelines.

Being superseded : Spring 5 introduced WebClient as the preferred non‑blocking alternative.

When to use RestTemplate

Simple CRUD use cases where synchronous behavior is acceptable.

Legacy codebases that already depend on RestTemplate.

Low‑traffic services or quick proof‑of‑concept prototypes.

WebClient

WebClient, added in Spring 5, is a non‑blocking, reactive HTTP client built on Project Reactor. It returns Mono<T> or Flux<T>, enabling fully asynchronous request handling without occupying threads.

Key features

Reactive API : Uses Mono and Flux to represent single‑value or multi‑value asynchronous streams.

Fluent builder : Chainable methods ( .get(), .uri(), .header(), .retrieve(), etc.) make request construction expressive.

Non‑blocking I/O : Under the hood uses Netty or the Java 11+ HttpClient, allowing thousands of concurrent connections with a small thread pool.

Spring ecosystem integration : Works with Spring Data Reactive, Spring Security, and other reactive modules.

Typical usage example

import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;

public class WebClientExample {
    public static void main(String[] args) {
        WebClient client = WebClient.create("https://funtester.com");
        Mono<String> responseMono = client.get()
                .uri("/posts/1")
                .retrieve()
                .bodyToMono(String.class);
        responseMono.subscribe(
                body -> System.out.println("Response Body: " + body),
                err -> System.err.println("Error: " + err.getMessage())
        );
        // Give the async pipeline time to complete (only for demo purposes)
        try { Thread.sleep(2000); } catch (InterruptedException ignored) {}
    }
}

Advantages

High throughput : Handles many concurrent requests with minimal thread usage.

Full reactive support : Naturally composes with other reactive streams.

Modern architecture compatibility : Ideal for microservices, event‑driven systems, and streaming APIs.

Limitations

Steeper learning curve : Requires understanding of reactive concepts (Mono, Flux, back‑pressure).

More complex error handling : Errors are propagated through the reactive pipeline and need explicit handling.

When to use WebClient

New projects that need non‑blocking I/O or high concurrency.

Microservice architectures where reactive streams are advantageous.

Scenarios involving streaming responses, server‑sent events, or WebSockets.

RestClient (Spring 6.1+)

RestClient is the latest Spring HTTP client introduced in Spring 6.1. It aims to combine the simplicity of RestTemplate with selective asynchronous capabilities, offering a fluent builder API and optional reactive integration.

Key features and improvements

Builder pattern : Requests are created via RestClient.builder(), providing a readable, chainable configuration.

Partial async support : Methods such as exchangeAsync() return CompletableFuture<ResponseEntity<T>>, giving non‑blocking behaviour without full reactive streams.

Reactive integration : When a reactor.core.publisher.Mono is desired, the client can be adapted to Project Reactor, allowing mixed usage.

Simplified error handling : Provides a unified RestClientException hierarchy and convenient status‑code checks.

Typical usage example

import org.springframework.web.client.RestClient;
import java.util.concurrent.CompletableFuture;

public class RestClientExample {
    public static void main(String[] args) {
        RestClient client = RestClient.builder()
                .baseUrl("https://funtester.com")
                .build();
        CompletableFuture<String> future = client.get()
                .uri("/posts/1")
                .retrieve()
                .bodyToMono(String.class) // optional: convert to Mono then to CompletableFuture
                .toFuture();
        future.thenAccept(body -> System.out.println("Async body: " + body))
              .exceptionally(ex -> { ex.printStackTrace(); return null; });
        // Block only for demo purposes
        future.join();
    }
}

When to use RestClient

Projects that need a balance between RestTemplate's simplicity and WebClient's async capabilities.

Applications that require asynchronous calls but do not want to adopt a full reactive stack.

Migration paths where existing RestTemplate code is being gradually upgraded.

Comparison of the three clients

Sync/Async : RestTemplate – synchronous only; WebClient – fully asynchronous/reactive; RestClient – supports both sync and CompletableFuture async.

API style : RestTemplate uses template‑method calls; WebClient and RestClient use fluent builders.

Reactive support : WebClient – full; RestClient – optional/partial; RestTemplate – none.

Performance under load : WebClient > RestClient > RestTemplate.

Complexity : RestTemplate – low; WebClient – high (reactive concepts); RestClient – moderate.

Spring version requirement : RestTemplate works with Spring 4/5; WebClient requires Spring 5+; RestClient requires Spring 6.1+.

Guidance

New projects : Prefer WebClient for its non‑blocking performance and reactive capabilities.

Existing RestTemplate codebases : Consider RestClient as a gradual migration path to introduce async features without a full reactive rewrite.

Simple, low‑traffic use cases : Continue using RestTemplate when synchronous calls and minimal complexity are sufficient.