WebClient

Similar to RestTemplate and AsyncRestTemplate, in the WebFlux stack, Spring adds a WebClient to perform HTTP requests and interact with HTTP APIs.

The following is a simple example of using WebClient to send a GET request to the /posts URI and retrieve posts.

WebClient client = WebClient.create("http://localhost:8080");
client
	.get()
	.uri("/posts")
	.exchange()
	.flatMapMany(res -> res.bodyToFlux(Post.class))
	.log()
	.subscribe(post -> System.out.println("post: " + post));

The WebClient provides a builder to configure ClientConnector, Codecs, ExchangeStrategies and change HttpHeaders. For example.

WebClient client = WebClient.builder()
    //see: https://github.com/jetty-project/jetty-reactive-httpclient
    //.clientConnector(new JettyClientHttpConnector())
    .clientConnector(new ReactorClientHttpConnector())
    .codecs(
    clientCodecConfigurer ->{
        // use defaultCodecs() to apply DefaultCodecs
        // clientCodecConfigurer.defaultCodecs();

        // alter a registered encoder/decoder based on the default config.
        // clientCodecConfigurer.defaultCodecs().jackson2Encoder(...)

        // Or
        // use customCodecs to register Codecs from scratch.
        clientCodecConfigurer.customCodecs().register(new Jackson2JsonDecoder());
        clientCodecConfigurer.customCodecs().register(new Jackson2JsonEncoder());
    }

)
    .exchangeStrategies(ExchangeStrategies.withDefaults())
    //                .exchangeFunction(ExchangeFunctions.create(new ReactorClientHttpConnector())
    //                        .filter(ExchangeFilterFunction.ofRequestProcessor(clientRequest -> {})))
    //                .filter(ExchangeFilterFunction.ofRequestProcessor(clientRequest -> {clientRequest.}))
    //.defaultHeaders(httpHeaders -> httpHeaders.addAll())
    .baseUrl("http://localhost:8080")
    .build();

By default, the ClientConnector is ReactorClientHttpConnector, there are some other built-in implementations:

• Jetty Reactive HttpClient
• Apache HttpComponents

For the complete codes, check spring-reactive-sample/client.

Another client utility class is WebTestClient , which is used for testing purpose.

The following is a simple example.

@WebFluxTest(controllers = MessageController.class)
public class DemoApplicationTests {

    @Autowired
    WebTestClient client;

    @Test
    public void getAllMessagesShouldBeOk() {
        client.get().uri("/").exchange().expectStatus().isOk();
    }

}

The usage of the WebTestClient API is very similar to WebClient, but provides methods to assert the response result.

NOTE: Although WebClient and WebTestClient looks similar, but WebTestClient is not derived from WebClient.