35. Calling REST Services with WebClient
If you have Spring WebFlux on your classpath, you can also choose to use WebClient to
call remote REST services. Compared to RestTemplate, this client has a more functional
feel and is fully reactive. You can create your own client instance with the builder,
WebClient.create(). See the relevant
section on WebClient.
Spring Boot creates and pre-configures such a builder for you. For example, client HTTP
codecs are configured in the same fashion as the server ones (see
WebFlux HTTP codecs auto-configuration).
The following code shows a typical example:
@Service
public class MyService {
private final WebClient webClient;
public MyService(WebClient.Builder webClientBuilder) {
this.webClient = webClientBuilder.baseUrl("https://example.org").build();
}
public Mono<Details> someRestCall(String name) {
return this.webClient.get().uri("/{name}/details", name)
.retrieve().bodyToMono(Details.class);
}
}
35.1 WebClient Customization
There are three main approaches to WebClient customization, depending on how broadly you
want the customizations to apply.
To make the scope of any customizations as narrow as possible, inject the auto-configured
WebClient.Builder and then call its methods as required. WebClient.Builder instances
are stateful: Any change on the builder is reflected in all clients subsequently created
with it. If you want to create several clients with the same builder, you can also
consider cloning the builder with WebClient.Builder other = builder.clone();.
To make an application-wide, additive customization to all WebClient.Builder instances,
you can declare WebClientCustomizer beans and change the WebClient.Builder locally at
the point of injection.
Finally, you can fall back to the original API and use WebClient.create(). In that case,
no auto-configuration or WebClientCustomizer is applied.