Allow ExchangeStrategies customizations in WebClient

Backport of d4209392 and acfeb77d

Closes gh-23961

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) {
@@ -93,6 +100,11 @@ final class DefaultExchangeStrategiesBuilder implements ExchangeStrategies.Build
 		public List<HttpMessageWriter<?>> messageWriters() {
 			return this.writers;
 		}
+
+		@Override
+		public Builder mutate() {
+			return new DefaultExchangeStrategiesBuilder(this);
+		}
 	}
 
 }

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

@@ -25,9 +25,11 @@ import java.util.function.Consumer;
 
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.client.reactive.ClientHttpConnector;
+import org.springframework.http.client.reactive.JettyClientHttpConnector;
 import org.springframework.http.client.reactive.ReactorClientHttpConnector;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -38,10 +40,22 @@ 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 {
 
+	private static final boolean reactorClientPresent;
+
+	private static final boolean jettyClientPresent;
+
+	static {
+		ClassLoader loader = DefaultWebClientBuilder.class.getClassLoader();
+		reactorClientPresent = ClassUtils.isPresent("reactor.netty.http.client.HttpClient", loader);
+		jettyClientPresent = ClassUtils.isPresent("org.eclipse.jetty.client.HttpClient", loader);
+	}
+
+
 	@Nullable
 	private String baseUrl;
 
@@ -66,14 +80,17 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 	@Nullable
 	private ClientHttpConnector connector;
 
-	private ExchangeStrategies exchangeStrategies;
+	@Nullable
+	private ExchangeStrategies strategies;
+
+	@Nullable
+	private List<Consumer<ExchangeStrategies.Builder>> strategiesConfigurers;
 
 	@Nullable
 	private ExchangeFunction exchangeFunction;
 
 
 	public DefaultWebClientBuilder() {
-		this.exchangeStrategies = ExchangeStrategies.withDefaults();
 	}
 
 	public DefaultWebClientBuilder(DefaultWebClientBuilder other) {
@@ -95,7 +112,7 @@ 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;
 	}
 
@@ -191,8 +208,16 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 
 	@Override
 	public WebClient.Builder exchangeStrategies(ExchangeStrategies strategies) {
-		Assert.notNull(strategies, "ExchangeStrategies must not be null");
-		this.exchangeStrategies = strategies;
+		this.strategies = strategies;
+		return this;
+	}
+
+	@Override
+	public WebClient.Builder exchangeStrategies(Consumer<ExchangeStrategies.Builder> configurer) {
+		if (this.strategiesConfigurers == null) {
+			this.strategiesConfigurers = new ArrayList<>(4);
+		}
+		this.strategiesConfigurers.add(configurer);
 		return this;
 	}
 
@@ -215,7 +240,9 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 
 	@Override
 	public WebClient build() {
-		ExchangeFunction exchange = initExchangeFunction();
+		ExchangeFunction exchange = (this.exchangeFunction == null ?
+				ExchangeFunctions.create(getOrInitConnector(), initExchangeStrategies()) :
+				this.exchangeFunction);
 		ExchangeFunction filteredExchange = (this.filters != null ? this.filters.stream()
 				.reduce(ExchangeFilterFunction::andThen)
 				.map(filter -> filter.apply(exchange))
@@ -226,16 +253,29 @@ final class DefaultWebClientBuilder implements WebClient.Builder {
 				this.defaultRequest, new DefaultWebClientBuilder(this));
 	}
 
-	private ExchangeFunction initExchangeFunction() {
-		if (this.exchangeFunction != null) {
-			return this.exchangeFunction;
+	private ClientHttpConnector getOrInitConnector() {
+		if (this.connector != null) {
+			return this.connector;
 		}
-		else if (this.connector != null) {
-			return ExchangeFunctions.create(this.connector, this.exchangeStrategies);
+		else if (reactorClientPresent) {
+			return new ReactorClientHttpConnector();
 		}
-		else {
-			return ExchangeFunctions.create(new ReactorClientHttpConnector(), this.exchangeStrategies);
+		else if (jettyClientPresent) {
+			return new JettyClientHttpConnector();
 		}
+		throw new IllegalStateException("No suitable default ClientHttpConnector found");
+	}
+
+	private ExchangeStrategies initExchangeStrategies() {
+		if (CollectionUtils.isEmpty(this.strategiesConfigurers)) {
+			return this.strategies != null ? this.strategies : ExchangeStrategies.withDefaults();
+		}
+
+		ExchangeStrategies.Builder builder =
+				this.strategies != null ? this.strategies.mutate() : ExchangeStrategies.builder();
+
+		this.strategiesConfigurers.forEach(configurer -> configurer.accept(builder));
+		return builder.build();
 	}
 
 	private UriBuilderFactory initUriBuilderFactory() {

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

@@ -47,6 +47,15 @@ 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
+	 */
+	default Builder mutate() {
+		throw new UnsupportedOperationException();
+	}
+
 
 	// Static builder methods
 

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

@@ -64,6 +64,7 @@ import org.springframework.web.util.UriBuilderFactory;
  *
  * @author Rossen Stoyanchev
  * @author Arjen Poutsma
+ * @author Brian Clozel
  * @since 5.0
  */
 public interface WebClient {
@@ -289,11 +290,25 @@ public interface WebClient {
 
 		/**
 		 * Configure the {@link ExchangeStrategies} to use.
-		 * <p>By default this is obtained from {@link ExchangeStrategies#withDefaults()}.
+		 * <p>Note that in a scenario where the builder is configured by
+		 * multiple parties, it is preferable to use
+		 * {@link #exchangeStrategies(Consumer)} in order to customize the same
+		 * {@code ExchangeStrategies}. This method here sets the strategies that
+		 * everyone else then can customize.
+		 * <p>By default this is {@link ExchangeStrategies#withDefaults()}.
 		 * @param strategies the strategies to use
 		 */
 		Builder exchangeStrategies(ExchangeStrategies strategies);
 
+		/**
+		 * Customize the strategies configured via
+		 * {@link #exchangeStrategies(ExchangeStrategies)}. This method is
+		 * designed for use in scenarios where multiple parties wish to update
+		 * the {@code ExchangeStrategies}.
+		 * @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 +39,16 @@ public class ExchangeStrategiesTests {
 		assertFalse(strategies.messageWriters().isEmpty());
 	}
 
+	@Test
+	@SuppressWarnings("deprecation")
+	public void mutate() {
+		ExchangeStrategies strategies = ExchangeStrategies.empty().build();
+		assertTrue(strategies.messageReaders().isEmpty());
+		assertTrue(strategies.messageWriters().isEmpty());
+
+		ExchangeStrategies mutated = strategies.mutate().codecs(codecs -> codecs.registerDefaults(true)).build();
+		assertFalse(mutated.messageReaders().isEmpty());
+		assertFalse(mutated.messageWriters().isEmpty());
+	}
+
 }