Use bean class loader when detecting ClientHttpRequestFactoryBuilder

Update `ClientHttpRequestFactoryBuilder` with a detect method that
accepts a specific classloader and update `HttpClientAutoConfiguration`
to use it.

Fixes gh-44986

Author: philwebb

Diff for: spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/client/AbstractHttpRequestFactoryProperties.java

@@ -48,11 +48,12 @@ public void setFactory(Factory factory) {
 
 	/**
 	 * Return a {@link ClientHttpRequestFactoryBuilder} based on the properties.
+	 * @param classLoader the class loader to use for detection
 	 * @return a {@link ClientHttpRequestFactoryBuilder}
 	 */
-	protected final ClientHttpRequestFactoryBuilder<?> factoryBuilder() {
+	protected final ClientHttpRequestFactoryBuilder<?> factoryBuilder(ClassLoader classLoader) {
 		Factory factory = getFactory();
-		return (factory != null) ? factory.builder() : ClientHttpRequestFactoryBuilder.detect();
+		return (factory != null) ? factory.builder() : ClientHttpRequestFactoryBuilder.detect(classLoader);
 	}
 
 	/**

Diff for: spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/http/client/HttpClientAutoConfiguration.java

@@ -18,6 +18,7 @@
 
 import java.util.List;
 
+import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfiguration;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -47,13 +48,20 @@
 @ConditionalOnClass(ClientHttpRequestFactory.class)
 @Conditional(NotReactiveWebApplicationCondition.class)
 @EnableConfigurationProperties(HttpClientProperties.class)
-public class HttpClientAutoConfiguration {
+public class HttpClientAutoConfiguration implements BeanClassLoaderAware {
+
+	private ClassLoader beanClassLoader;
+
+	@Override
+	public void setBeanClassLoader(ClassLoader classLoader) {
+		this.beanClassLoader = classLoader;
+	}
 
 	@Bean
 	@ConditionalOnMissingBean
 	ClientHttpRequestFactoryBuilder<?> clientHttpRequestFactoryBuilder(HttpClientProperties httpClientProperties,
 			ObjectProvider<ClientHttpRequestFactoryBuilderCustomizer<?>> clientHttpRequestFactoryBuilderCustomizers) {
-		ClientHttpRequestFactoryBuilder<?> builder = httpClientProperties.factoryBuilder();
+		ClientHttpRequestFactoryBuilder<?> builder = httpClientProperties.factoryBuilder(this.beanClassLoader);
 		return customize(builder, clientHttpRequestFactoryBuilderCustomizers.orderedStream().toList());
 	}
 

Diff for: spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/http/client/HttpClientAutoConfigurationTests.java

@@ -28,8 +28,11 @@
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings;
 import org.springframework.boot.http.client.ClientHttpRequestFactorySettings.Redirects;
 import org.springframework.boot.http.client.HttpComponentsClientHttpRequestFactoryBuilder;
+import org.springframework.boot.http.client.JdkClientHttpRequestFactoryBuilder;
 import org.springframework.boot.http.client.JettyClientHttpRequestFactoryBuilder;
+import org.springframework.boot.http.client.ReactorClientHttpRequestFactoryBuilder;
 import org.springframework.boot.http.client.SimpleClientHttpRequestFactoryBuilder;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.boot.test.context.runner.ReactiveWebApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -87,6 +90,32 @@ private List<String> sslPropertyValues() {
 		return propertyValues;
 	}
 
+	@Test
+	void whenHttpComponentsIsUnavailableThenJettyClientBeansAreDefined() {
+		this.contextRunner
+			.withClassLoader(new FilteredClassLoader(org.apache.hc.client5.http.impl.classic.HttpClients.class))
+			.run((context) -> assertThat(context.getBean(ClientHttpRequestFactoryBuilder.class))
+				.isExactlyInstanceOf(JettyClientHttpRequestFactoryBuilder.class));
+	}
+
+	@Test
+	void whenHttpComponentsAndJettyAreUnavailableThenReactorClientBeansAreDefined() {
+		this.contextRunner
+			.withClassLoader(new FilteredClassLoader(org.apache.hc.client5.http.impl.classic.HttpClients.class,
+					org.eclipse.jetty.client.HttpClient.class))
+			.run((context) -> assertThat(context.getBean(ClientHttpRequestFactoryBuilder.class))
+				.isExactlyInstanceOf(ReactorClientHttpRequestFactoryBuilder.class));
+	}
+
+	@Test
+	void whenHttpComponentsAndJettyAndReactorAreUnavailableThenJdkClientBeansAreDefined() {
+		this.contextRunner
+			.withClassLoader(new FilteredClassLoader(org.apache.hc.client5.http.impl.classic.HttpClients.class,
+					org.eclipse.jetty.client.HttpClient.class, reactor.netty.http.client.HttpClient.class))
+			.run((context) -> assertThat(context.getBean(ClientHttpRequestFactoryBuilder.class))
+				.isExactlyInstanceOf(JdkClientHttpRequestFactoryBuilder.class));
+	}
+
 	@Test
 	void whenReactiveWebApplicationBeansAreNotConfigured() {
 		new ReactiveWebApplicationContextRunner().withConfiguration(autoConfigurations)

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/ClientHttpRequestFactoryBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -196,16 +196,34 @@ static <T extends ClientHttpRequestFactory> ClientHttpRequestFactoryBuilder<T> o
 	 * @return the most suitable {@link ClientHttpRequestFactoryBuilder} for the classpath
 	 */
 	static ClientHttpRequestFactoryBuilder<? extends ClientHttpRequestFactory> detect() {
-		if (HttpComponentsClientHttpRequestFactoryBuilder.Classes.PRESENT) {
+		return detect(null);
+	}
+
+	/**
+	 * Detect the most suitable {@link ClientHttpRequestFactoryBuilder} based on the
+	 * classpath. The methods favors builders in the following order:
+	 * <ol>
+	 * <li>{@link #httpComponents()}</li>
+	 * <li>{@link #jetty()}</li>
+	 * <li>{@link #reactor()}</li>
+	 * <li>{@link #jdk()}</li>
+	 * <li>{@link #simple()}</li>
+	 * </ol>
+	 * @param classLoader the class loader to use for detection
+	 * @return the most suitable {@link ClientHttpRequestFactoryBuilder} for the classpath
+	 * @since 3.5.0
+	 */
+	static ClientHttpRequestFactoryBuilder<? extends ClientHttpRequestFactory> detect(ClassLoader classLoader) {
+		if (HttpComponentsClientHttpRequestFactoryBuilder.Classes.present(classLoader)) {
 			return httpComponents();
 		}
-		if (JettyClientHttpRequestFactoryBuilder.Classes.PRESENT) {
+		if (JettyClientHttpRequestFactoryBuilder.Classes.present(classLoader)) {
 			return jetty();
 		}
-		if (ReactorClientHttpRequestFactoryBuilder.Classes.PRESENT) {
+		if (ReactorClientHttpRequestFactoryBuilder.Classes.present(classLoader)) {
 			return reactor();
 		}
-		if (JdkClientHttpRequestFactoryBuilder.Classes.PRESENT) {
+		if (JdkClientHttpRequestFactoryBuilder.Classes.present(classLoader)) {
 			return jdk();
 		}
 		return simple();

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/HttpComponentsClientHttpRequestFactoryBuilder.java

@@ -156,7 +156,9 @@ static class Classes {
 
 		static final String HTTP_CLIENTS = "org.apache.hc.client5.http.impl.classic.HttpClients";
 
-		static final boolean PRESENT = ClassUtils.isPresent(HTTP_CLIENTS, null);
+		static boolean present(ClassLoader classLoader) {
+			return ClassUtils.isPresent(HTTP_CLIENTS, classLoader);
+		}
 
 	}
 

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/JdkClientHttpRequestFactoryBuilder.java

@@ -86,7 +86,9 @@ static class Classes {
 
 		static final String HTTP_CLIENT = "java.net.http.HttpClient";
 
-		static final boolean PRESENT = ClassUtils.isPresent(HTTP_CLIENT, null);
+		static boolean present(ClassLoader classLoader) {
+			return ClassUtils.isPresent(HTTP_CLIENT, classLoader);
+		}
 
 	}
 

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/JettyClientHttpRequestFactoryBuilder.java

@@ -116,7 +116,9 @@ static class Classes {
 
 		static final String HTTP_CLIENT = "org.eclipse.jetty.client.HttpClient";
 
-		static final boolean PRESENT = ClassUtils.isPresent(HTTP_CLIENT, null);
+		static boolean present(ClassLoader classLoader) {
+			return ClassUtils.isPresent(HTTP_CLIENT, classLoader);
+		}
 
 	}
 

Diff for: spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/ReactorClientHttpRequestFactoryBuilder.java

@@ -91,7 +91,9 @@ static class Classes {
 
 		static final String HTTP_CLIENT = "reactor.netty.http.client.HttpClient";
 
-		static final boolean PRESENT = ClassUtils.isPresent(HTTP_CLIENT, null);
+		static boolean present(ClassLoader classLoader) {
+			return ClassUtils.isPresent(HTTP_CLIENT, classLoader);
+		}
 
 	}