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Configuration

The simplest way to create a WebClient is through one of the static factory methods:

  • WebClient.create()

  • WebClient.create(String baseUrl)

You can also use WebClient.builder() with further options:

  • uriBuilderFactory: Customized UriBuilderFactory to use as a base URL.

  • defaultUriVariables: default values to use when expanding URI templates.

  • defaultHeader: Headers for every request.

  • defaultCookie: Cookies for every request.

  • defaultRequest: Consumer to customize every request.

  • filter: Client filter for every request.

  • exchangeStrategies: HTTP message reader/writer customizations.

  • clientConnector: HTTP client library settings.

  • observationRegistry: the registry to use for enabling Observability support.

  • observationConvention: an optional, custom convention to extract metadata for recorded observations.

For example:

Java
WebClient client = WebClient.builder()
		.codecs(configurer -> ... )
		.build();
Kotlin
val webClient = WebClient.builder()
		.codecs { configurer -> ... }
		.build()

Once built, a WebClient is immutable. However, you can clone it and build a modified copy as follows:

Java
WebClient client1 = WebClient.builder()
		.filter(filterA).filter(filterB).build();

WebClient client2 = client1.mutate()
		.filter(filterC).filter(filterD).build();

// client1 has filterA, filterB

// client2 has filterA, filterB, filterC, filterD
Kotlin
val client1 = WebClient.builder()
		.filter(filterA).filter(filterB).build()

val client2 = client1.mutate()
		.filter(filterC).filter(filterD).build()

// client1 has filterA, filterB

// client2 has filterA, filterB, filterC, filterD

MaxInMemorySize

Codecs have limits for buffering data in memory to avoid application memory issues. By default those are set to 256KB. If that’s not enough you’ll get the following error:

org.springframework.core.io.buffer.DataBufferLimitException: Exceeded limit on max bytes to buffer

To change the limit for default codecs, use the following:

Java
WebClient webClient = WebClient.builder()
		.codecs(configurer -> configurer.defaultCodecs().maxInMemorySize(2 * 1024 * 1024))
		.build();
Kotlin
val webClient = WebClient.builder()
		.codecs { configurer -> configurer.defaultCodecs().maxInMemorySize(2 * 1024 * 1024) }
		.build()

Reactor Netty

To customize Reactor Netty settings, provide a pre-configured HttpClient:

Java
HttpClient httpClient = HttpClient.create().secure(sslSpec -> ...);

WebClient webClient = WebClient.builder()
		.clientConnector(new ReactorClientHttpConnector(httpClient))
		.build();
Kotlin
val httpClient = HttpClient.create().secure { ... }

val webClient = WebClient.builder()
	.clientConnector(ReactorClientHttpConnector(httpClient))
	.build()

Resources

By default, HttpClient participates in the global Reactor Netty resources held in reactor.netty.http.HttpResources, including event loop threads and a connection pool. This is the recommended mode, since fixed, shared resources are preferred for event loop concurrency. In this mode global resources remain active until the process exits.

If the server is timed with the process, there is typically no need for an explicit shutdown. However, if the server can start or stop in-process (for example, a Spring MVC application deployed as a WAR), you can declare a Spring-managed bean of type ReactorResourceFactory with globalResources=true (the default) to ensure that the Reactor Netty global resources are shut down when the Spring ApplicationContext is closed, as the following example shows:

Java
@Bean
public ReactorResourceFactory reactorResourceFactory() {
	return new ReactorResourceFactory();
}
Kotlin
@Bean
fun reactorResourceFactory() = ReactorResourceFactory()

You can also choose not to participate in the global Reactor Netty resources. However, in this mode, the burden is on you to ensure that all Reactor Netty client and server instances use shared resources, as the following example shows:

Java
@Bean
public ReactorResourceFactory resourceFactory() {
	ReactorResourceFactory factory = new ReactorResourceFactory();
	factory.setUseGlobalResources(false); // (1)
	return factory;
}

@Bean
public WebClient webClient() {

	Function<HttpClient, HttpClient> mapper = client -> {
		// Further customizations...
	};

	ClientHttpConnector connector =
			new ReactorClientHttpConnector(resourceFactory(), mapper); // (2)

	return WebClient.builder().clientConnector(connector).build(); // (3)
}

  1. Create resources independent of global ones.

  2. Use the ReactorClientHttpConnector constructor with resource factory.

  3. Plug the connector into the WebClient.Builder.

Kotlin
@Bean
fun resourceFactory() = ReactorResourceFactory().apply {
	isUseGlobalResources = false // (1)
}

@Bean
fun webClient(): WebClient {

	val mapper: (HttpClient) -> HttpClient = {
		// Further customizations...
	}

	val connector = ReactorClientHttpConnector(resourceFactory(), mapper) // (2)

	return WebClient.builder().clientConnector(connector).build() // (3)
}

  1. Create resources independent of global ones.

  2. Use the ReactorClientHttpConnector constructor with resource factory.

  3. Plug the connector into the WebClient.Builder.

Timeouts

To configure a connection timeout:

Java
import io.netty.channel.ChannelOption;

HttpClient httpClient = HttpClient.create()
		.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000);

WebClient webClient = WebClient.builder()
		.clientConnector(new ReactorClientHttpConnector(httpClient))
		.build();
Kotlin
import io.netty.channel.ChannelOption

val httpClient = HttpClient.create()
		.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000);

val webClient = WebClient.builder()
		.clientConnector(ReactorClientHttpConnector(httpClient))
		.build();

To configure a read or write timeout:

Java
import io.netty.handler.timeout.ReadTimeoutHandler;
import io.netty.handler.timeout.WriteTimeoutHandler;

HttpClient httpClient = HttpClient.create()
		.doOnConnected(conn -> conn
				.addHandlerLast(new ReadTimeoutHandler(10))
				.addHandlerLast(new WriteTimeoutHandler(10)));

// Create WebClient...
Kotlin
import io.netty.handler.timeout.ReadTimeoutHandler
import io.netty.handler.timeout.WriteTimeoutHandler

val httpClient = HttpClient.create()
		.doOnConnected { conn -> conn
				.addHandlerLast(ReadTimeoutHandler(10))
				.addHandlerLast(WriteTimeoutHandler(10))
		}

// Create WebClient...

To configure a response timeout for all requests:

Java
HttpClient httpClient = HttpClient.create()
		.responseTimeout(Duration.ofSeconds(2));

// Create WebClient...
Kotlin
val httpClient = HttpClient.create()
		.responseTimeout(Duration.ofSeconds(2));

// Create WebClient...

To configure a response timeout for a specific request:

Java
WebClient.create().get()
		.uri("https://example.org/path")
		.httpRequest(httpRequest -> {
			HttpClientRequest reactorRequest = httpRequest.getNativeRequest();
			reactorRequest.responseTimeout(Duration.ofSeconds(2));
		})
		.retrieve()
		.bodyToMono(String.class);
Kotlin
WebClient.create().get()
		.uri("https://example.org/path")
		.httpRequest { httpRequest: ClientHttpRequest ->
			val reactorRequest = httpRequest.getNativeRequest<HttpClientRequest>()
			reactorRequest.responseTimeout(Duration.ofSeconds(2))
		}
		.retrieve()
		.bodyToMono(String::class.java)

JDK HttpClient

The following example shows how to customize the JDK HttpClient:

Java
HttpClient httpClient = HttpClient.newBuilder()
    .followRedirects(Redirect.NORMAL)
    .connectTimeout(Duration.ofSeconds(20))
    .build();

ClientHttpConnector connector =
        new JdkClientHttpConnector(httpClient, new DefaultDataBufferFactory());

WebClient webClient = WebClient.builder().clientConnector(connector).build();
Kotlin
val httpClient = HttpClient.newBuilder()
    .followRedirects(Redirect.NORMAL)
    .connectTimeout(Duration.ofSeconds(20))
    .build()

val connector = JdkClientHttpConnector(httpClient, DefaultDataBufferFactory())

val webClient = WebClient.builder().clientConnector(connector).build()

Jetty

The following example shows how to customize Jetty HttpClient settings:

Java
HttpClient httpClient = new HttpClient();
httpClient.setCookieStore(...);

WebClient webClient = WebClient.builder()
		.clientConnector(new JettyClientHttpConnector(httpClient))
		.build();
Kotlin
val httpClient = HttpClient()
httpClient.cookieStore = ...

val webClient = WebClient.builder()
		.clientConnector(JettyClientHttpConnector(httpClient))
		.build();

By default, HttpClient creates its own resources (Executor, ByteBufferPool, Scheduler), which remain active until the process exits or stop() is called.

You can share resources between multiple instances of the Jetty client (and server) and ensure that the resources are shut down when the Spring ApplicationContext is closed by declaring a Spring-managed bean of type JettyResourceFactory, as the following example shows:

Java
@Bean
public JettyResourceFactory resourceFactory() {
	return new JettyResourceFactory();
}

@Bean
public WebClient webClient() {

	HttpClient httpClient = new HttpClient();
	// Further customizations...

	ClientHttpConnector connector =
			new JettyClientHttpConnector(httpClient, resourceFactory()); (1)

	return WebClient.builder().clientConnector(connector).build(); (2)
}

  1. Use the JettyClientHttpConnector constructor with resource factory.

  2. Plug the connector into the WebClient.Builder.

Kotlin
@Bean
fun resourceFactory() = JettyResourceFactory()

@Bean
fun webClient(): WebClient {

	val httpClient = HttpClient()
	// Further customizations...

	val connector = JettyClientHttpConnector(httpClient, resourceFactory()) // (1)

	return WebClient.builder().clientConnector(connector).build() // (2)
}

  1. Use the JettyClientHttpConnector constructor with resource factory.

  2. Plug the connector into the WebClient.Builder.

HttpComponents

The following example shows how to customize Apache HttpComponents HttpClient settings:

Java
HttpAsyncClientBuilder clientBuilder = HttpAsyncClients.custom();
clientBuilder.setDefaultRequestConfig(...);
CloseableHttpAsyncClient client = clientBuilder.build();

ClientHttpConnector connector = new HttpComponentsClientHttpConnector(client);

WebClient webClient = WebClient.builder().clientConnector(connector).build();
Kotlin
val client = HttpAsyncClients.custom().apply {
	setDefaultRequestConfig(...)
}.build()
val connector = HttpComponentsClientHttpConnector(client)
val webClient = WebClient.builder().clientConnector(connector).build()