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 learn more about the WebClient in the dedicated
section in the Spring Framework docs.
Spring Boot creates and pre-configures a WebClient.Builder for you; it is strongly
advised to inject it in your components and use it to create WebClient instances.
Spring Boot is configuring that builder to share HTTP resources, reflect codecs
setup in the same fashion as the server ones (see
WebFlux HTTP codecs auto-configuration), and more.
The following code shows a typical example:
@Service public class MyService { private final WebClient webClient; public MyService(WebClient.Builder webClientBuilder) { this.webClient = webClientBuilder.baseUrl("http://example.org").build(); } public Mono<Details> someRestCall(String name) { return this.webClient.get().uri("/{name}/details", name) .retrieve().bodyToMono(Details.class); } }
Spring Boot will auto-detect which ClientHttpConnector to use to drive WebClient,
depending on the libraries available on the application classpath. For now, Reactor
Netty and Jetty RS client are supported.
The spring-boot-starter-webflux starter depends on io.projectreactor.netty:reactor-netty
by default, which brings both server and client implementations. If you choose to use Jetty
as a reactive server instead, you should add a dependency on the Jetty Reactive HTTP
client library, org.eclipse.jetty:jetty-reactive-httpclient. Using the same technology
for server and client has it advantages, as it will automatically share HTTP resources
between client and server.
Developers can override the resource configuration for Jetty and Reactor Netty by providing
a custom ReactorResourceFactory or JettyResourceFactory bean - this will be applied to
both clients and servers.
If you wish to override that choice for the client, you can define your own
ClientHttpConnector bean and have full control over the client configuration.
You can learn more about the
WebClient configuration
options in the Spring Framework reference documentation.
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.