Allow ExchangeStrategies customizations in WebClient

Prior to this commit, developers could configure their WebClient to use
their custom `ExchangeStrategies`, by providing it in the
`WebClient.Builder` chain.
Once created, an `ExchangeStrategies` instance is not mutable, which
makes it hard for further customizations by other components. In the
case of the reported issue, other components would override the default
configuration for the codecs maxInMemorySize.

This commit makes the `ExchangeStrategies` mutable and uses that fact to
further customize them with a new `WebClient.Builder#exchangeStrategies`
`Consumer` variant. This commit is also deprecating those mutating
variants in favor of a new `WebClient.Builder#exchangeStrategies` that
takes a `ExchangeStrategies#Builder` directly and avoids mutation issues
altogether.

Closes gh-23961

spring-messaging/src/main/java/org/springframework/messaging/rsocket/RSocketRequester.java

@@ -169,18 +169,19 @@ public interface RSocketRequester {
 		RSocketRequester.Builder setupMetadata(Object value, @Nullable MimeType mimeType);
 
 		/**
-		 * Provide {@link RSocketStrategies} to use.
-		 * <p>By default this is based on default settings of
-		 * {@link RSocketStrategies.Builder} but may be further customized via
-		 * {@link #rsocketStrategies(Consumer)}.
+		 * Provide the {@link RSocketStrategies} to use.
+		 * <p>This is useful for changing the default settings, yet still allowing
+		 * further customizations via {@link #rsocketStrategies(Consumer)}.
+		 * If not set, defaults are obtained from {@link RSocketStrategies#builder()}.
+		 * @param strategies the strategies to use
 		 */
 		RSocketRequester.Builder rsocketStrategies(@Nullable RSocketStrategies strategies);
 
 		/**
 		 * Customize the {@link RSocketStrategies}.
-		 * <p>By default this starts out as {@link RSocketStrategies#builder()}.
-		 * However if strategies were {@link #rsocketStrategies(RSocketStrategies) set}
-		 * explicitly, then they are {@link RSocketStrategies#mutate() mutated}.
+		 * <p>Allows further customization on {@link RSocketStrategies},
+		 * mutating them if they were {@link #rsocketStrategies(RSocketStrategies) set},
+		 * or starting from {@link RSocketStrategies#builder()} defaults}.
 		 */
 		RSocketRequester.Builder rsocketStrategies(Consumer<RSocketStrategies.Builder> configurer);
 

spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClientBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -137,11 +137,24 @@ class DefaultWebTestClientBuilder implements WebTestClient.Builder {
 	}
 
 	@Override
+	@Deprecated
 	public WebTestClient.Builder exchangeStrategies(ExchangeStrategies strategies) {
 		this.webClientBuilder.exchangeStrategies(strategies);
 		return this;
 	}
 
+	@Override
+	public WebTestClient.Builder exchangeStrategies(ExchangeStrategies.Builder strategies) {
+		this.webClientBuilder.exchangeStrategies(strategies);
+		return this;
+	}
+
+	@Override
+	public WebTestClient.Builder exchangeStrategies(Consumer<ExchangeStrategies.Builder> configurer) {
+		this.webClientBuilder.exchangeStrategies(configurer);
+		return this;
+	}
+
 	@Override
 	public WebTestClient.Builder responseTimeout(Duration timeout) {
 		this.responseTimeout = timeout;

spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java

@@ -84,6 +84,7 @@ import org.springframework.web.util.UriBuilderFactory;
  * perform integration tests on an embedded WebFlux server.
  *
  * @author Rossen Stoyanchev
+ * @author Brian Clozel
  * @since 5.0
  * @see StatusAssertions
  * @see HeaderAssertions
@@ -443,11 +444,34 @@ public interface WebTestClient {
 
 		/**
 		 * Configure the {@link ExchangeStrategies} to use.
-		 * <p>By default {@link ExchangeStrategies#withDefaults()} is used.
+		 * <p>This is useful for changing the default settings, yet still allowing
+		 * further customizations via {@link #exchangeStrategies(Consumer)}.
+		 * By default {@link ExchangeStrategies#withDefaults()} is used.
 		 * @param strategies the strategies to use
+		 * @deprecated as of 5.1 in favor of {@link #exchangeStrategies(ExchangeStrategies.Builder)}
 		 */
+		@Deprecated
 		Builder exchangeStrategies(ExchangeStrategies strategies);
 
+		/**
+		 * Configure the {@link ExchangeStrategies.Builder} to use.
+		 * <p>This is useful for changing the default settings, yet still allowing
+		 * further customizations via {@link #exchangeStrategies(Consumer)}.
+		 * By default {@link ExchangeStrategies#builder()} is used.
+		 * @param strategies the strategies to use
+		 * @since 5.1.12
+		 */
+		Builder exchangeStrategies(ExchangeStrategies.Builder strategies);
+
+		/**
+		 * Customize the {@link ExchangeStrategies}.
+		 * <p>Allows further customization on {@link ExchangeStrategies},
+		 * mutating them if they were {@link #exchangeStrategies(ExchangeStrategies) set},
+		 * or starting from {@link ExchangeStrategies#withDefaults() defaults}.
+		 * @since 5.1.12
+		 */
+		Builder exchangeStrategies(Consumer<ExchangeStrategies.Builder> configurer);
+
 		/**
 		 * Max amount of time to wait for responses.
 		 * <p>By default 5 seconds.
@@ -928,7 +952,7 @@ public interface WebTestClient {
 		 * @since 5.1
 		 * @see #xpath(String, Map, Object...)
 		 */
-		default XpathAssertions xpath(String expression, Object... args){
+		default XpathAssertions xpath(String expression, Object... args) {
 			return xpath(expression, null, args);
 		}
 
@@ -942,7 +966,7 @@ public interface WebTestClient {
 		 * @param args arguments to parameterize the expression
 		 * @since 5.1
 		 */
-		XpathAssertions xpath(String expression, @Nullable  Map<String, String> namespaces, Object... args);
+		XpathAssertions xpath(String expression, @Nullable Map<String, String> namespaces, Object... args);
 
 		/**
 		 * Assert the response body content with the given {@link Consumer}.

spring-web/src/main/java/org/springframework/http/codec/ClientCodecConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -63,6 +63,11 @@ public interface ClientCodecConfigurer extends CodecConfigurer {
 	@Override
 	ClientDefaultCodecs defaultCodecs();
 
+	/**
+	 * Clone this {@link ClientCodecConfigurer}.
+	 */
+	@Override
+	ClientCodecConfigurer clone();
 
 	/**
 	 * Static factory method for a {@code ClientCodecConfigurer}.

spring-web/src/main/java/org/springframework/http/codec/CodecConfigurer.java

@@ -87,6 +87,12 @@ public interface CodecConfigurer {
 	 */
 	List<HttpMessageWriter<?>> getWriters();
 
+	/**
+	 * Clone this {@link CodecConfigurer}.
+	 * @since 5.1.12
+	 */
+	CodecConfigurer clone();
+
 
 	/**
 	 * Customize or replace the HTTP message readers and writers registered by

spring-web/src/main/java/org/springframework/http/codec/support/BaseCodecConfigurer.java

@@ -34,13 +34,14 @@ import org.springframework.util.Assert;
  * client and server specific variants.
  *
  * @author Rossen Stoyanchev
+ * @author Brian Clozel
  * @since 5.0
  */
 class BaseCodecConfigurer implements CodecConfigurer {
 
-	private final BaseDefaultCodecs defaultCodecs;
+	protected final BaseDefaultCodecs defaultCodecs;
 
-	private final DefaultCustomCodecs customCodecs = new DefaultCustomCodecs();
+	protected final DefaultCustomCodecs customCodecs;
 
 
 	/**
@@ -50,6 +51,16 @@ class BaseCodecConfigurer implements CodecConfigurer {
 	BaseCodecConfigurer(BaseDefaultCodecs defaultCodecs) {
 		Assert.notNull(defaultCodecs, "'defaultCodecs' is required");
 		this.defaultCodecs = defaultCodecs;
+		this.customCodecs = new DefaultCustomCodecs();
+	}
+
+	/**
+	 * Constructor with another {@link BaseCodecConfigurer} to copy
+	 * the configuration from.
+	 */
+	BaseCodecConfigurer(BaseCodecConfigurer other) {
+		this.defaultCodecs = other.cloneDefaultCodecs();
+		this.customCodecs = new DefaultCustomCodecs(other.customCodecs);
 	}
 
 
@@ -87,6 +98,17 @@ class BaseCodecConfigurer implements CodecConfigurer {
 		return getWritersInternal(false);
 	}
 
+
+	@Override
+	public CodecConfigurer clone() {
+		return new BaseCodecConfigurer(this);
+	}
+
+	protected BaseDefaultCodecs cloneDefaultCodecs() {
+		return new BaseDefaultCodecs(this.defaultCodecs);
+	}
+
+
 	/**
 	 * Internal method that returns the configured writers.
 	 * @param forMultipart whether to returns writers for general use ("false"),
@@ -110,7 +132,7 @@ class BaseCodecConfigurer implements CodecConfigurer {
 	/**
 	 * Default implementation of {@code CustomCodecs}.
 	 */
-	private static final class DefaultCustomCodecs implements CustomCodecs {
+	protected static final class DefaultCustomCodecs implements CustomCodecs {
 
 		private final List<HttpMessageReader<?>> typedReaders = new ArrayList<>();
 
@@ -121,6 +143,16 @@ class BaseCodecConfigurer implements CodecConfigurer {
 		private final List<HttpMessageWriter<?>> objectWriters = new ArrayList<>();
 
 
+		DefaultCustomCodecs() {
+		}
+
+		DefaultCustomCodecs(DefaultCustomCodecs other) {
+			other.typedReaders.addAll(this.typedReaders);
+			other.typedWriters.addAll(this.typedWriters);
+			other.objectReaders.addAll(this.objectReaders);
+			other.objectWriters.addAll(this.objectWriters);
+		}
+
 		@Override
 		public void decoder(Decoder<?> decoder) {
 			reader(new DecoderHttpMessageReader<>(decoder));
@@ -143,7 +175,6 @@ class BaseCodecConfigurer implements CodecConfigurer {
 			(canWriteObject ? this.objectWriters : this.typedWriters).add(writer);
 		}
 
-
 		// Package private accessors...
 
 		List<HttpMessageReader<?>> getTypedReaders() {

spring-web/src/main/java/org/springframework/http/codec/support/BaseDefaultCodecs.java

@@ -106,6 +106,21 @@ class BaseDefaultCodecs implements CodecConfigurer.DefaultCodecs {
 	private boolean registerDefaults = true;
 
 
+	BaseDefaultCodecs() {
+	}
+
+	protected BaseDefaultCodecs(BaseDefaultCodecs other) {
+		this.jackson2JsonDecoder = other.jackson2JsonDecoder;
+		this.jackson2JsonEncoder = other.jackson2JsonEncoder;
+		this.protobufDecoder = other.protobufDecoder;
+		this.protobufEncoder = other.protobufEncoder;
+		this.jaxb2Decoder = other.jaxb2Decoder;
+		this.jaxb2Encoder = other.jaxb2Encoder;
+		this.maxInMemorySize = other.maxInMemorySize;
+		this.enableLoggingRequestDetails = other.enableLoggingRequestDetails;
+		this.registerDefaults = other.registerDefaults;
+	}
+
 	@Override
 	public void jackson2JsonDecoder(Decoder<?> decoder) {
 		this.jackson2JsonDecoder = decoder;

spring-web/src/main/java/org/springframework/http/codec/support/ClientDefaultCodecsImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -49,6 +49,17 @@ class ClientDefaultCodecsImpl extends BaseDefaultCodecs implements ClientCodecCo
 	private Supplier<List<HttpMessageWriter<?>>> partWritersSupplier;
 
 
+	ClientDefaultCodecsImpl() {
+	}
+
+	ClientDefaultCodecsImpl(ClientDefaultCodecsImpl other) {
+		super(other);
+		this.multipartCodecs = new DefaultMultipartCodecs(other.multipartCodecs);
+		this.sseDecoder = other.sseDecoder;
+		this.partWritersSupplier = other.partWritersSupplier;
+	}
+
+
 	/**
 	 * Set a supplier for part writers to use when
 	 * {@link #multipartCodecs()} are not explicitly configured.
@@ -73,6 +84,14 @@ class ClientDefaultCodecsImpl extends BaseDefaultCodecs implements ClientCodecCo
 		this.sseDecoder = decoder;
 	}
 
+	@Override
+	public ClientDefaultCodecsImpl clone() {
+		ClientDefaultCodecsImpl codecs = new ClientDefaultCodecsImpl();
+		codecs.multipartCodecs = this.multipartCodecs;
+		codecs.sseDecoder = this.sseDecoder;
+		codecs.partWritersSupplier = this.partWritersSupplier;
+		return codecs;
+	}
 
 	@Override
 	protected void extendObjectReaders(List<HttpMessageReader<?>> objectReaders) {
@@ -116,6 +135,17 @@ class ClientDefaultCodecsImpl extends BaseDefaultCodecs implements ClientCodecCo
 
 		private final List<HttpMessageWriter<?>> writers = new ArrayList<>();
 
+
+		DefaultMultipartCodecs() {
+		}
+
+		DefaultMultipartCodecs(@Nullable DefaultMultipartCodecs other) {
+			if (other != null) {
+				this.writers.addAll(other.writers);
+			}
+		}
+
+
 		@Override
 		public ClientCodecConfigurer.MultipartCodecs encoder(Encoder<?> encoder) {
 			writer(new EncoderHttpMessageWriter<>(encoder));

spring-web/src/main/java/org/springframework/http/codec/support/DefaultClientCodecConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,14 +26,30 @@ import org.springframework.http.codec.ClientCodecConfigurer;
  */
 public class DefaultClientCodecConfigurer extends BaseCodecConfigurer implements ClientCodecConfigurer {
 
+
 	public DefaultClientCodecConfigurer() {
 		super(new ClientDefaultCodecsImpl());
 		((ClientDefaultCodecsImpl) defaultCodecs()).setPartWritersSupplier(() -> getWritersInternal(true));
 	}
 
+	private DefaultClientCodecConfigurer(DefaultClientCodecConfigurer other) {
+		super(other);
+	}
+
+
 	@Override
 	public ClientDefaultCodecs defaultCodecs() {
 		return (ClientDefaultCodecs) super.defaultCodecs();
 	}
 
+	@Override
+	public DefaultClientCodecConfigurer clone() {
+		return new DefaultClientCodecConfigurer(this);
+	}
+
+	@Override
+	protected BaseDefaultCodecs cloneDefaultCodecs() {
+		return new ClientDefaultCodecsImpl((ClientDefaultCodecsImpl) defaultCodecs());
+	}
+
 }

spring-web/src/main/java/org/springframework/http/codec/support/DefaultServerCodecConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,13 +26,28 @@ import org.springframework.http.codec.ServerCodecConfigurer;
  */
 public class DefaultServerCodecConfigurer extends BaseCodecConfigurer implements ServerCodecConfigurer {
 
+
 	public DefaultServerCodecConfigurer() {
 		super(new ServerDefaultCodecsImpl());
 	}
 
+	private DefaultServerCodecConfigurer(BaseCodecConfigurer other) {
+		super(other);
+	}
+
+
 	@Override
 	public ServerDefaultCodecs defaultCodecs() {
 		return (ServerDefaultCodecs) super.defaultCodecs();
 	}
 
+	@Override
+	public DefaultServerCodecConfigurer clone() {
+		return new DefaultServerCodecConfigurer(this);
+	}
+
+	@Override
+	protected BaseDefaultCodecs cloneDefaultCodecs() {
+		return new ServerDefaultCodecsImpl((ServerDefaultCodecsImpl) defaultCodecs());
+	}
 }

spring-web/src/main/java/org/springframework/http/codec/support/ServerDefaultCodecsImpl.java

@@ -46,6 +46,16 @@ class ServerDefaultCodecsImpl extends BaseDefaultCodecs implements ServerCodecCo
 	private Encoder<?> sseEncoder;
 
 
+	ServerDefaultCodecsImpl() {
+	}
+
+	ServerDefaultCodecsImpl(ServerDefaultCodecsImpl other) {
+		super(other);
+		this.multipartReader = other.multipartReader;
+		this.sseEncoder = other.sseEncoder;
+	}
+
+
 	@Override
 	public void multipartReader(HttpMessageReader<?> reader) {
 		this.multipartReader = reader;

spring-web/src/test/java/org/springframework/http/codec/support/CodecConfigurerTests.java

@@ -268,6 +268,14 @@ public class CodecConfigurerTests {
 		assertEncoderInstance(jaxb2Encoder);
 	}
 
+	@Test
+	public void cloneConfigurer() {
+		CodecConfigurer clone = this.configurer.clone();
+		this.configurer.registerDefaults(false);
+		assertThat(this.configurer.getReaders().size()).isEqualTo(0);
+		assertThat(clone.getReaders().size()).isEqualTo(11);
+	}
+
 	private Decoder<?> getNextDecoder(List<HttpMessageReader<?>> readers) {
 		HttpMessageReader<?> reader = readers.get(this.index.getAndIncrement());
 		assertThat(reader.getClass()).isEqualTo(DecoderHttpMessageReader.class);

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultExchangeStrategiesBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,13 +42,18 @@ final class DefaultExchangeStrategiesBuilder implements ExchangeStrategies.Build
 	}
 
 
-	private final ClientCodecConfigurer codecConfigurer = ClientCodecConfigurer.create();
+	private final ClientCodecConfigurer codecConfigurer;
 
 
 	public DefaultExchangeStrategiesBuilder() {
+		this.codecConfigurer = ClientCodecConfigurer.create();
 		this.codecConfigurer.registerDefaults(false);
 	}
 
+	private DefaultExchangeStrategiesBuilder(DefaultExchangeStrategies other) {
+		this.codecConfigurer = other.codecConfigurer.clone();
+	}
+
 
 	public void defaultConfiguration() {
 		this.codecConfigurer.registerDefaults(true);
@@ -62,21 +67,23 @@ final class DefaultExchangeStrategiesBuilder implements ExchangeStrategies.Build
 
 	@Override
 	public ExchangeStrategies build() {
-		return new DefaultExchangeStrategies(
-				this.codecConfigurer.getReaders(), this.codecConfigurer.getWriters());
+		return new DefaultExchangeStrategies(this.codecConfigurer);
 	}
 
 
 	private static class DefaultExchangeStrategies implements ExchangeStrategies {
 
+		private final ClientCodecConfigurer codecConfigurer;
+
 		private final List<HttpMessageReader<?>> readers;
 
 		private final List<HttpMessageWriter<?>> writers;
 
 
-		public DefaultExchangeStrategies(List<HttpMessageReader<?>> readers, List<HttpMessageWriter<?>> writers) {
-			this.readers = unmodifiableCopy(readers);
-			this.writers = unmodifiableCopy(writers);
+		public DefaultExchangeStrategies(ClientCodecConfigurer codecConfigurer) {
+			this.codecConfigurer = codecConfigurer;
+			this.readers = unmodifiableCopy(this.codecConfigurer.getReaders());
+			this.writers = unmodifiableCopy(this.codecConfigurer.getWriters());
 		}
 
 		private static <T> List<T> unmodifiableCopy(List<? extends T> list) {
@@ -84,6 +91,12 @@ final class DefaultExchangeStrategiesBuilder implements ExchangeStrategies.Build
 		}
 
 
+		@Override
+		@Deprecated
+		public Builder mutate() {
+			return new DefaultExchangeStrategiesBuilder(this);
+		}
+
 		@Override
 		public List<HttpMessageReader<?>> messageReaders() {
 			return this.readers;

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultWebClientBuilder.java

@@ -40,6 +40,7 @@ import org.springframework.web.util.UriBuilderFactory;
  * Default implementation of {@link WebClient.Builder}.
  *
  * @author Rossen Stoyanchev
+ * @author Brian Clozel
  * @since 5.0
  */
 final class DefaultWebClientBuilder implements WebClient.Builder {
@@ -79,14 +80,16 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	@Nullable
 	private ClientHttpConnector connector;
 
-	private ExchangeStrategies exchangeStrategies;
+	@Nullable
+	private ExchangeStrategies.Builder strategies;
+
+	private List<Consumer<ExchangeStrategies.Builder>> strategiesConfigurers;
 
 	@Nullable
 	private ExchangeFunction exchangeFunction;
 
 
 	public DefaultWebClientBuilder() {
-		this.exchangeStrategies = ExchangeStrategies.withDefaults();
 	}
 
 	public DefaultWebClientBuilder(DefaultWebClientBuilder other) {
@@ -108,7 +111,7 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 		this.defaultRequest = other.defaultRequest;
 		this.filters = other.filters != null ? new ArrayList<>(other.filters) : null;
 		this.connector = other.connector;
-		this.exchangeStrategies = other.exchangeStrategies;
+		this.strategies = other.strategies;
 		this.exchangeFunction = other.exchangeFunction;
 	}
 
@@ -203,9 +206,23 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	}
 
 	@Override
+	@Deprecated
 	public WebClient.Builder exchangeStrategies(ExchangeStrategies strategies) {
 		Assert.notNull(strategies, "ExchangeStrategies must not be null");
-		this.exchangeStrategies = strategies;
+		this.strategies = strategies.mutate();
+		return this;
+	}
+
+	@Override
+	public WebClient.Builder exchangeStrategies(ExchangeStrategies.Builder strategies) {
+		Assert.notNull(strategies, "ExchangeStrategies must not be null");
+		this.strategies = strategies;
+		return this;
+	}
+
+	@Override
+	public WebClient.Builder exchangeStrategies(Consumer<ExchangeStrategies.Builder> configurer) {
+		this.strategiesConfigurers.add(configurer);
 		return this;
 	}
 
@@ -229,7 +246,7 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	@Override
 	public WebClient build() {
 		ExchangeFunction exchange = (this.exchangeFunction == null ?
-				ExchangeFunctions.create(getOrInitConnector(), this.exchangeStrategies) :
+				ExchangeFunctions.create(getOrInitConnector(), initExchangeStrategies()) :
 				this.exchangeFunction);
 		ExchangeFunction filteredExchange = (this.filters != null ? this.filters.stream()
 				.reduce(ExchangeFilterFunction::andThen)
@@ -254,6 +271,19 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 		throw new IllegalStateException("No suitable default ClientHttpConnector found");
 	}
 
+	@SuppressWarnings("deprecation")
+	private ExchangeStrategies initExchangeStrategies() {
+		if (CollectionUtils.isEmpty(this.strategiesConfigurers)) {
+			return this.strategies != null ? this.strategies.build() : ExchangeStrategies.withDefaults();
+		}
+
+		ExchangeStrategies.Builder builder =
+				this.strategies != null ? this.strategies : ExchangeStrategies.builder();
+
+		this.strategiesConfigurers.forEach(configurer -> configurer.accept(builder));
+		return builder.build();
+	}
+
 	private UriBuilderFactory initUriBuilderFactory() {
 		if (this.uriBuilderFactory != null) {
 			return this.uriBuilderFactory;

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/ExchangeStrategies.java

@@ -47,6 +47,18 @@ public interface ExchangeStrategies {
 	 */
 	List<HttpMessageWriter<?>> messageWriters();
 
+	/**
+	 * Return a builder to create a new {@link ExchangeStrategies} instance
+	 * replicated from the current instance.
+	 * @since 5.1.12
+	 * @deprecated APIs should consume {@link ExchangeStrategies} as final or accept an
+	 * {@link ExchangeStrategies.Builder builder}.
+	 */
+	@Deprecated
+	default Builder mutate() {
+		throw new UnsupportedOperationException("This ExchangeStrategies implementation does not support mutation.");
+	}
+
 
 	// Static builder methods
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/WebClient.java

@@ -66,6 +66,7 @@ import org.springframework.web.util.UriBuilderFactory;
  * @author Rossen Stoyanchev
  * @author Arjen Poutsma
  * @author Sebastien Deleuze
+ * @author Brian Clozel
  * @since 5.0
  */
 public interface WebClient {
@@ -290,12 +291,35 @@ public interface WebClient {
 		Builder clientConnector(ClientHttpConnector connector);
 
 		/**
-		 * Configure the {@link ExchangeStrategies} to use.
-		 * <p>By default this is obtained from {@link ExchangeStrategies#withDefaults()}.
+		 * Provide the {@link ExchangeStrategies} to use.
+		 * <p>This is useful for changing the default settings, yet still allowing
+		 * further customizations via {@link #exchangeStrategies(Consumer)}.
+		 * If not set, defaults are obtained from {@link ExchangeStrategies#withDefaults()}.
 		 * @param strategies the strategies to use
+		 * @deprecated as of 5.1, in favor of {@link #exchangeStrategies(ExchangeStrategies.Builder)}
 		 */
+		@Deprecated
 		Builder exchangeStrategies(ExchangeStrategies strategies);
 
+		/**
+		 * Provide the {@link ExchangeStrategies.Builder} to use.
+		 * <p>This is useful for changing the default settings, yet still allowing
+		 * further customizations via {@link #exchangeStrategies(Consumer)}.
+		 * If not set, defaults are obtained from {@link ExchangeStrategies#builder()}.
+		 * @param strategies the strategies to use
+		 * @since 5.1.12
+		 */
+		Builder exchangeStrategies(ExchangeStrategies.Builder strategies);
+
+		/**
+		 * Customize the {@link ExchangeStrategies}.
+		 * <p>Allows further customization on {@link ExchangeStrategies},
+		 * mutating them if they were {@link #exchangeStrategies(ExchangeStrategies) set},
+		 * or starting from {@link ExchangeStrategies#withDefaults() defaults}.
+		 * @since 5.1.12
+		 */
+		Builder exchangeStrategies(Consumer<ExchangeStrategies.Builder> configurer);
+
 		/**
 		 * Provide an {@link ExchangeFunction} pre-configured with
 		 * {@link ClientHttpConnector} and {@link ExchangeStrategies}.

spring-webflux/src/test/java/org/springframework/web/reactive/function/client/ExchangeStrategiesTests.java

@@ -39,4 +39,15 @@ public class ExchangeStrategiesTests {
 		assertThat(strategies.messageWriters().isEmpty()).isFalse();
 	}
 
+	@Test
+	@SuppressWarnings("deprecation")
+	public void mutate() {
+		ExchangeStrategies strategies = ExchangeStrategies.empty().build();
+		assertThat(strategies.messageReaders().isEmpty()).isTrue();
+		assertThat(strategies.messageWriters().isEmpty()).isTrue();
+		ExchangeStrategies mutated = strategies.mutate().codecs(codecs -> codecs.registerDefaults(true)).build();
+		assertThat(mutated.messageReaders().isEmpty()).isFalse();
+		assertThat(mutated.messageWriters().isEmpty()).isFalse();
+	}
+
 }

src/docs/asciidoc/web/webflux-webclient.adoc

@@ -41,28 +41,26 @@ The following example configures <<web-reactive.adoc#webflux-codecs, HTTP codecs
 [source,java,indent=0,subs="verbatim,quotes",role="primary"]
 .Java
 ----
-	ExchangeStrategies strategies = ExchangeStrategies.builder()
-			.codecs(configurer -> {
-				// ...
-			})
-			.build();
+	Consumer<ExchangeStrategies.Builder> customizeCodecs = builder -> {
+		builder.codecs(configurer -> {
+			//...
+		});
+	};
 
 	WebClient client = WebClient.builder()
-			.exchangeStrategies(strategies)
+			.exchangeStrategies(customizeCodecs)
 			.build();
 ----
 [source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
 .Kotlin
 ----
-	val strategies = ExchangeStrategies.builder()
-			.codecs {
-				// ...
+	val webClient = WebClient.builder()
+			.exchangeStrategies { strategies ->
+				strategies.codecs {
+					//...
+				}
 			}
 			.build()
-
-	val client = WebClient.builder()
-			.exchangeStrategies(strategies)
-			.build()
 ----
 
 Once built, a `WebClient` instance is immutable. However, you can clone it and build a
@@ -95,7 +93,44 @@ modified copy without affecting the original instance, as the following example
 	// client2 has filterA, filterB, filterC, filterD
 ----
 
+[[webflux-client-builder-maxinmemorysize]]
+=== MaxInMemorySize
+
+Spring WebFlux configures by default a maximum size for buffering data in-memory when decoding
+HTTP responses with the `WebClient`. This avoids application memory issues if the received
+response is much larger than expected.
+
+The default configured value of 256KB might not be enough for your use case, and your application
+might hit that limit with the following:
+
+----
+org.springframework.core.io.buffer.DataBufferLimitException: Exceeded limit on max bytes to buffer
+----
+
+You can configure this limit on all default codecs with the following code sample:
 
+[source,java,indent=0,subs="verbatim,quotes",role="primary"]
+.Java
+----
+	WebClient webClient = WebClient.builder()
+			.exchangeStrategies(configurer ->
+				configurer.codecs(codecs ->
+					codecs.defaultCodecs().maxInMemorySize(2 * 1024 * 1024)
+				)
+			)
+			.build();
+----
+[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
+.Kotlin
+----
+	val webClient = WebClient.builder()
+		.exchangeStrategies { strategies ->
+				strategies.codecs {
+					it.defaultCodecs().maxInMemorySize(2 * 1024 * 1024)
+				}
+		}
+		.build()
+----
 
 [[webflux-client-builder-reactor]]
 === Reactor Netty