RestClient vs. WebClient: Choosing the Right REST Client in Spring Boot

When building Spring Boot applications, one of the first decisions you’ll make is choosing the HTTP client for communicating with other services.

For years, RestTemplate was the standard solution. Today, WebClient is the recommended choice for new applications.

But is WebClient always the better option?

Let’s compare both approaches and discuss one often-overlooked topic: how to properly log outgoing requests and responses when using WebClient.

RestTemplate

RestTemplate provides a simple, synchronous programming model.

Example:

ResponseEntity<OrderResponse> response =
    restTemplate.getForEntity(url, OrderResponse.class);

The calling thread blocks until the remote service responds.

Advantages

• Very easy to understand
• Simple debugging
• Large amount of existing documentation
• Suitable for traditional Spring MVC applications

Disadvantages

• One thread per request
• Poor scalability under high latency
• Considered maintenance mode by Spring

Although still fully supported, Spring recommends using WebClient for new development.

WebClient

WebClient is part of Spring WebFlux and supports asynchronous, non-blocking HTTP communication.

Example:

Mono<OrderResponse> response =
    webClient.get()
             .uri("/orders/{id}", id)
             .retrieve()
             .bodyToMono(OrderResponse.class);

No thread is blocked while waiting for the response.

Blocking vs Non-Blocking

The biggest architectural difference is the threading model.

RestClient

Thread
   |
   |---- HTTP Request ---------------- Waiting ---------------- Response

The thread remains occupied for the entire duration.

WebClient

Thread
   |
   |---- Send Request
            |
            |---- Event Loop waits for response
            |
         Callback executes when response arrives

The application can process many more concurrent requests with fewer threads.

Does Every Application Need WebClient?

Not necessarily.

For internal business applications with moderate traffic, RestClient may still be perfectly adequate.

The benefits of WebClient become significant when:

• calling many remote services
• handling thousands of concurrent requests
• building reactive applications
• dealing with slow external APIs

Choosing WebClient simply because it is newer is not always the right decision.

A Common Mistake: Using WebClient as a Blocking Client

Many applications do this:

OrderResponse response = webClient.get()
    .uri(...)
    .retrieve()
    .bodyToMono(OrderResponse.class)
    .block();

Technically, it works.

However, calling .block() removes most of WebClient’s advantages.

You still pay the complexity of reactive programming while falling back to synchronous execution.

If your application is fully synchronous, using RestClient may actually produce cleaner and more maintainable code.

Logging with RestClient

Logging requests is relatively straightforward.

A ClientHttpRequestInterceptor can inspect:

• URL
• HTTP method
• Headers
• Request body
• Response body
• Execution time

Many logging libraries support this approach directly.

Logging with WebClient

Logging is more challenging.

The request and response travel through a reactive pipeline and are processed asynchronously.

Many developers initially attempt something like:

.doOnNext(log::info)

Unfortunately, this only logs the response body and provides little context.

Use ExchangeFilterFunction

The recommended approach is using ExchangeFilterFunction.

Logging:

ExchangeFilterFunction loggingFilter = (request, next) -> {

    long start = System.currentTimeMillis();

    log.info("→ {} {}", request.method(), request.url());

    return next.exchange(request)
        .doOnNext(response ->
            log.info("← {} {} ({} ms)",
                response.statusCode(),
                request.url(),
                System.currentTimeMillis() - start)
        )
        .doOnError(ex ->
            log.error("✕ {} {} ({} ms)",
                request.method(),
                request.url(),
                System.currentTimeMillis() - start,
                ex)
        );
};

Register the filter:

WebClient.builder()
    .filter(loggingFilter)
    .build();

This keeps logging separated from business logic.

Logging Request and Response Bodies

Logging bodies is considerably more difficult.

Unlike RestClient, the body is represented as a reactive stream.

Once consumed, it cannot simply be read again.

Attempting to log the body incorrectly may:

• consume the stream
• break downstream processing
• increase memory usage

For this reason, logging complete payloads should generally be avoided in production.

Instead, log:

• HTTP method
• URI
• Status code
• Execution time
• Correlation ID

This provides sufficient operational visibility while avoiding performance issues and accidental logging of sensitive information.

Measuring Request Duration

A useful pattern is measuring execution time.

long start = System.currentTimeMillis();

webClient.get()
    .uri(...)
    .retrieve()
    .bodyToMono(OrderResponse.class)
    .doFinally(signal ->
        log.info("Request completed in {} ms",
            System.currentTimeMillis() - start));

Latency information is often more valuable than the response body itself.

Correlation IDs

In microservices, every outgoing request should propagate the current correlation ID.

Example:

WebClient.builder()
    .defaultHeader("X-Correlation-ID", correlationId)
    .build();

Combined with centralized logging, this allows tracing a request across multiple services.

Which One Should You Choose?

Final Thoughts

Neither client is universally better.

RestClient remains an excellent choice for many synchronous applications because of its simplicity.

WebClient shines when scalability, asynchronous processing, and high concurrency become important.

If you choose WebClient, don’t stop at replacing the HTTP client.

Also invest in:

• proper timeout configuration
• centralized logging
• correlation IDs
• metrics
• resilience patterns

Without observability, debugging distributed systems quickly becomes one of the hardest parts of operating a microservice architecture.

Key Takeaways

• RestClient is synchronous and easy to use.
• WebClient is asynchronous and more scalable.
• Avoid calling .block() unless absolutely necessary.
• Use ExchangeFilterFunction for centralized request and response logging.
• Prefer logging metadata over complete payloads.
• Always propagate correlation IDs between services.
• Configure timeouts regardless of which client you choose.