Provide auto-configuration for using Apache HttpClient 5 with WebClient

Closes gh-26004

spring-boot-project/spring-boot-autoconfigure/build.gradle

@@ -56,6 +56,7 @@ dependencies {
 	optional("org.apache.activemq:artemis-jms-client")
 	optional("org.apache.activemq:artemis-jms-server")
 	optional("org.apache.commons:commons-dbcp2")
+	optional("org.apache.httpcomponents.client5:httpclient5")
 	optional("org.apache.kafka:kafka-streams")
 	optional("org.apache.solr:solr-solrj")
 	optional("org.apache.tomcat.embed:tomcat-embed-core")

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/function/client/ClientHttpConnectorAutoConfiguration.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -40,7 +40,8 @@ import org.springframework.web.reactive.function.client.WebClient;
  */
 @Configuration(proxyBeanMethods = false)
 @ConditionalOnClass(WebClient.class)
-@Import({ ClientHttpConnectorConfiguration.ReactorNetty.class, ClientHttpConnectorConfiguration.JettyClient.class })
+@Import({ ClientHttpConnectorConfiguration.ReactorNetty.class, ClientHttpConnectorConfiguration.JettyClient.class,
+		ClientHttpConnectorConfiguration.HttpClient5.class })
 public class ClientHttpConnectorAutoConfiguration {
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/reactive/function/client/ClientHttpConnectorConfiguration.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.boot.autoconfigure.web.reactive.function.client;
 
+import org.apache.hc.client5.http.impl.async.HttpAsyncClients;
+import org.apache.hc.core5.http.nio.AsyncRequestProducer;
 import org.eclipse.jetty.client.HttpClient;
 import org.eclipse.jetty.util.ssl.SslContextFactory;
 
@@ -26,6 +28,7 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.http.client.reactive.ClientHttpConnector;
+import org.springframework.http.client.reactive.HttpComponentsClientHttpConnector;
 import org.springframework.http.client.reactive.JettyClientHttpConnector;
 import org.springframework.http.client.reactive.JettyResourceFactory;
 import org.springframework.http.client.reactive.ReactorClientHttpConnector;
@@ -45,17 +48,17 @@ class ClientHttpConnectorConfiguration {
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(reactor.netty.http.client.HttpClient.class)
 	@ConditionalOnMissingBean(ClientHttpConnector.class)
-	public static class ReactorNetty {
+	static class ReactorNetty {
 
 		@Bean
 		@ConditionalOnMissingBean
-		public ReactorResourceFactory reactorClientResourceFactory() {
+		ReactorResourceFactory reactorClientResourceFactory() {
 			return new ReactorResourceFactory();
 		}
 
 		@Bean
 		@Lazy
-		public ReactorClientHttpConnector reactorClientHttpConnector(ReactorResourceFactory reactorResourceFactory,
+		ReactorClientHttpConnector reactorClientHttpConnector(ReactorResourceFactory reactorResourceFactory,
 				ObjectProvider<ReactorNettyHttpClientMapper> mapperProvider) {
 			ReactorNettyHttpClientMapper mapper = mapperProvider.orderedStream()
 					.reduce((before, after) -> (client) -> after.configure(before.configure(client)))
@@ -68,17 +71,17 @@ class ClientHttpConnectorConfiguration {
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnClass(org.eclipse.jetty.reactive.client.ReactiveRequest.class)
 	@ConditionalOnMissingBean(ClientHttpConnector.class)
-	public static class JettyClient {
+	static class JettyClient {
 
 		@Bean
 		@ConditionalOnMissingBean
-		public JettyResourceFactory jettyClientResourceFactory() {
+		JettyResourceFactory jettyClientResourceFactory() {
 			return new JettyResourceFactory();
 		}
 
 		@Bean
 		@Lazy
-		public JettyClientHttpConnector jettyClientHttpConnector(JettyResourceFactory jettyResourceFactory) {
+		JettyClientHttpConnector jettyClientHttpConnector(JettyResourceFactory jettyResourceFactory) {
 			SslContextFactory sslContextFactory = new SslContextFactory.Client();
 			HttpClient httpClient = new HttpClient(sslContextFactory);
 			return new JettyClientHttpConnector(httpClient, jettyResourceFactory);
@@ -86,4 +89,17 @@ class ClientHttpConnectorConfiguration {
 
 	}
 
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnClass({ HttpAsyncClients.class, AsyncRequestProducer.class })
+	@ConditionalOnMissingBean(ClientHttpConnector.class)
+	static class HttpClient5 {
+
+		@Bean
+		@Lazy
+		HttpComponentsClientHttpConnector httpComponentsClientHttpConnector() {
+			return new HttpComponentsClientHttpConnector();
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/reactive/function/client/ClientHttpConnectorAutoConfigurationTests.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -16,10 +16,13 @@
 
 package org.springframework.boot.autoconfigure.web.reactive.function.client;
 
+import org.eclipse.jetty.reactive.client.ReactiveRequest;
 import org.junit.jupiter.api.Test;
+import reactor.netty.http.client.HttpClient;
 
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.boot.web.reactive.function.client.WebClientCustomizer;
 import org.springframework.context.annotation.Bean;
@@ -46,7 +49,7 @@ class ClientHttpConnectorAutoConfigurationTests {
 			.withConfiguration(AutoConfigurations.of(ClientHttpConnectorAutoConfiguration.class));
 
 	@Test
-	void shouldCreateResourcesLazily() {
+	void whenReactorIsAvailableThenReactorBeansAreDefined() {
 		this.contextRunner.run((context) -> {
 			BeanDefinition customizerDefinition = context.getBeanFactory()
 					.getBeanDefinition("clientConnectorCustomizer");
@@ -54,9 +57,35 @@ class ClientHttpConnectorAutoConfigurationTests {
 			BeanDefinition connectorDefinition = context.getBeanFactory()
 					.getBeanDefinition("reactorClientHttpConnector");
 			assertThat(connectorDefinition.isLazyInit()).isTrue();
+			assertThat(context).hasBean("reactorClientResourceFactory");
 		});
 	}
 
+	@Test
+	void whenReactorIsUnavailableThenJettyBeansAreDefined() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader(HttpClient.class)).run((context) -> {
+			BeanDefinition customizerDefinition = context.getBeanFactory()
+					.getBeanDefinition("clientConnectorCustomizer");
+			assertThat(customizerDefinition.isLazyInit()).isTrue();
+			BeanDefinition connectorDefinition = context.getBeanFactory().getBeanDefinition("jettyClientHttpConnector");
+			assertThat(connectorDefinition.isLazyInit()).isTrue();
+			assertThat(context).hasBean("jettyClientResourceFactory");
+		});
+	}
+
+	@Test
+	void whenReactorAndJettyAreUnavailableThenHttpClientBeansAreDefined() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader(HttpClient.class, ReactiveRequest.class))
+				.run((context) -> {
+					BeanDefinition customizerDefinition = context.getBeanFactory()
+							.getBeanDefinition("clientConnectorCustomizer");
+					assertThat(customizerDefinition.isLazyInit()).isTrue();
+					BeanDefinition connectorDefinition = context.getBeanFactory()
+							.getBeanDefinition("httpComponentsClientHttpConnector");
+					assertThat(connectorDefinition.isLazyInit()).isTrue();
+				});
+	}
+
 	@Test
 	void shouldCreateHttpClientBeans() {
 		this.contextRunner.run((context) -> {

spring-boot-project/spring-boot-dependencies/build.gradle

@@ -483,14 +483,33 @@ bom {
 			]
 		}
 	}
+	library("HttpClient5", "5.0.3") {
+		group("org.apache.httpcomponents.client5") {
+			modules = [
+				"httpclient5",
+				"httpclient5-cache",
+				"httpclient5-fluent",
+				"httpclient5-win",
+			]
+		}
+	}
 	library("HttpCore", "4.4.14") {
-		group("org.apache.httpcomponents") {
+		group("org.apache.httpcomponents.core5") {
 			modules = [
 				"httpcore",
 				"httpcore-nio"
 			]
 		}
 	}
+	library("HttpCore5", "5.1") {
+		group("org.apache.httpcomponents") {
+			modules = [
+				"httpcore5",
+				"httpcore5-h2",
+				"httpcore5-reactive"
+			]
+		}
+	}
 	library("Infinispan", "12.0.2.Final") {
 		group("org.infinispan") {
 			imports = [