RestClient (Spring 6.1+) — fluent synchronous client replacing RestTemplate.

RestClient (Spring 6.1+) is the modern fluent, synchronous HTTP client — WebClient's ergonomics without needing Reactor. It's the forward path for blocking HTTP calls; RestTemplate is in maintenance mode (still supported, not formally deprecated) but won't get new features.

Why it exists

RestTemplate works but its API is template-method-style and awkward for anything beyond simple getForObject. WebClient has a much nicer fluent API but pulls in the reactive stack and returns Mono/Flux, which is overkill if your code is plain blocking. RestClient takes WebClient's fluent, chained API and makes it synchronous — you get the readable builder style and direct return values.

RestClient client = RestClient.create("https://orders.internal");

Order order = client.get()
    .uri("/orders/{id}", 42)
    .accept(MediaType.APPLICATION_JSON)
    .retrieve()
    .body(Order.class);          // blocks, returns the value directly

POST and error handling read naturally:

Order created = client.post()
    .uri("/orders")
    .body(new NewOrder("widget"))
    .retrieve()
    .onStatus(HttpStatusCode::is4xxClientError,
        (req, res) -> { throw new OrderClientException(res.getStatusCode()); })
    .body(Order.class);

For full control, .toEntity(Order.class) returns a ResponseEntity; .exchange(...) hands you the raw request/response.

Status in the ecosystem

• It reuses the same ClientHttpRequestFactory infrastructure as RestTemplate, so you can migrate incrementally and even build a RestClient from an existing RestTemplate.
• It backs @HttpExchange interfaces via RestClientAdapter, so declarative clients can run on a blocking transport.
• RestTemplate is not deprecated — existing code keeps working — but new code should prefer RestClient. State this precisely; claiming RestTemplate is "deprecated" is a common but wrong answer.